Experimental Aspects of Laser and Electron-Beam Produced

IAEA-182

EXPERIMENTAL ASPECTS OF LASED RAN ELECTRON-BEAM PRODUCED THERMONUCLEAR PLASMAS

PROCEEDINGS OF AN ADVISORY GROUP MEETING EXPERIMENTAN O L ASPECT LASEF SO D RAN ELECTRON-BEAM PRODUCED THERMONUCLEAR PLASMAS HEL TRIESTET DA , 25-29 AUGUST 1975 ORGANIZED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY TOG ETHER WITH THE INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS, TRIESTE

A TECHNICAL DOCUMENT ISSUED E BYTH INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1976 PLEASE BE AWARE THAT MISSINE TH AL F LO G PAGES IN THIS DOCUMENT WERE ORIGINALLY BLANK IAEe Th A doe t maintaisno n stock f reportso thin si s series. However, microfiche copies of these reports can be obtained from INIS Microfiche Clearinghouse International Atomic Energy Agency Kamtner Ring 11 0 59 P.Ox Bo . A-1011 Vienna, Austria on prepayment of US $0.65 or against one I AEAmicrofiche service coupon. D R W0 E R 0 P

The Advisory Group Meeting on Experimental Aspects of Laser and Electron-Beam Produced Thermonuclear Plasmas was organized by the Agency together with the International Center for Theoretical Physic follow-ua Triesten i ss e wa th t f I .o p Worksho Theoretican po l Problem f Laseo s r Blectron-Beam Plasma Interactio nTrieste helth t da e Cente Augusn i r t 1973 scientist7 2 . s from 10 countries attended the meeting. meetine e coursfirse th dayo th th f e preseno stw f n t gI th o e t f experimento t ar e statlasen th electron-bea o d sf eo an r m produced plasmas were reviewed by the representatives of several major laboratorie includee ar d san thin d i s publication. Workshop-type sessions on the following selected topics were held? 1. Laser systems 2. Interaction of laser beam with target plasma 3* Laser heating for magnetic confinement &» Diagnosti f implosioo c n 5. Reactor concepts. Short resumes of these sessions prepared by the chairmen together with four original papers presented at the meeting are included in this report. The participants also exchanged their possible viewth n o s e rol f smalleeo r experiment e lase electron-bead th an rn i s m fusion programme with the aim to give guidelines to developing countries which would lik staro et t researc thin hi s field. The facilities provided for this meeting by the ICTP were excellent and the Agency would like to acknowledge the personal efforts of Professor Budini and Dr. Hamende of the Center who contributed to the success of the meeting. Tabl Contentf eo s

NATIONA LABORATORD LAN Y REPORTS Laser fusion

Laser fusion researc Japan hi n C. Yamanaka Laser fusion research at the Lebedev Institute of Physics of the USSR Academy of Sciences ...... 5 V. Gribkov Laser fusion research at Los Alamos .••••«•«•«•••••••••••••••••• 9 1 Mc1 . 0 H Ca . Review of BRDA inertial confinement fusion efforts ...... 21 G. W. K u s w a Laser fusion research at the Centre d1 Etudes de Limeil,Franee .. 27 J.P. Babuel-Peyrissac and J.P. Watt e a u Laser fusion research in UK «•»••••••*•••••••«••«*•*••••«•**•«•• 29 . SpaldinJ . I g Laser research at the Institute of Applied Physics, University of Bernei Switzerland »•»»••••••»•••»•••»••»••••»•••••»•••»• H. W e b e r Electron-beam produced fusion Research at the I.V. Kurchatov Institute of Atomic Energy on the powerfuf o e us l electron beam initiato st epulsea d thermo- L. I. Rudakov Electron beam researc Sandit ha a Laboratories, USA...... 3 4 . sa n o G .Y REB Institutfusioe th t na Plasmf eo a Physios, Nagoya University, ^•••"••••••••••••••••••••••••••••••••••••••••••••••*N .. A Ja.na.t i * 49

SUMMARIES OF THE SESSIONS

H* J* D o u c e t Interaction of laser radiation with plasma ••••••••••••••••••••• 55 P. Sigel and V. S i 1 i n Laser heatin magnetir gfo c confinement ••••••••••••••••••••••••9 5 • I. Spalding Implosion diagnostics using X-rays .•••«....•..•••••»«•»•••••••• 63 J.P. Babuel-Peyri s s a c and G. W. K u s w a role smalleTh f eo r experiment lasee th rn s i fusio n programm • e• 65 M. Gryzinski

CONTRIBUTED PAPERS Laser interaction with plasma ••«•*••••••»»«••*•••«•••«**•«••••• 69 ad , hi s o Y . K , i k a s a S . gn T , a K . H , . i MJ i zu T.Tschudi, N. YamaguchijT. Yamanaka, C* Yamanaka Plasma heatin intensy gb e relativistic electron-beam ...... 5 9 . K. ImasakitS. Nakai , C. Yamanaka Some reactor implication lasef so relativistir r(o c beam)7 fusio10 • n• I. Spalding Laser induced non-linear plasma phenomena (self phase modulation of light) and anomalous absorption of REB in plasma ••••••••••••••• 113 C. Yamanaka List of participants •••••••••••••••••••••••••••••••••••••••••••••• 117 NATIONA LABORATORD LAN Y REPORTS

Laser Fusion LASER FUSION RESEARCH IN JAPAN C. Yamanaka Institute of Laser Engineering, Osaka University, Osaka

Summary?

The following main aims are being pursued in the field of laser fusion researc Institute th t ha f Laseeo r Engineering, Osaka IfoiversityJ - Developmen f higo t h power high efficiency lasers - Stud f physicyo f laseo s r coupling with plasma.. - Development of diagnostics of fine spacial ( /urn) and temporal (psec) resolution ' - Development of technique of a pellet compression* High power Nd glass laser GEKKO syste E-bead man m excite . lasedCO r LEKKO system are being developed for these purposes. GEKKO I - one beam glass laser system with 7 amplifiers, energy output , lasens 2 r n beai J m 0 diamete5 ms 0 i m4 wits i r hdivergenca e being less than 0.5 m rad, pulse widt s adjustablhi e tenfrow mfe s picosecondo t s nanoseconds. GEKKd GEKKan OI O I e correspondingl IVar four-bead an o ytw m systems with an energy of 250 J in each beam. A twelve-beam glass laser wit htota a 0*n i 5J l K nse energ0 s 1 i c f yo being planned. The results achieved with the GEKKO system up to-day are the following: Parametric decay instabilit s yclarifiei d experimentally inducee Th . d backward Brillouin scattering observed nea e seconth r d harmonice th f o s reflected light shows an isotope effect due to the ion acoustic waves in hydrogen and deuterium plasma respectively. A decrease of the reflectivity of the laser light from plasma was ascertained at the laser intensity of ten times larger than the threshold of the parametric decay instability. Spectral broadenine self-phasth o t e gdu e modulatio observes e nwa th n di backscattered wavelengte lighth n i t h 1.06 /urn. Acceleration mechanismf o s fast ion was investigated. A compression experiment is investigated using glass micro balloon filled with D_ gas. LEKKO I - is high pressure E-beam C02 laser with two stages of TEA laser preamplifie three-staged an r mai2 sC0 n amplifier outpue th n !i J t 0 energ20 s yi one nanosecond. LEKKO III, a two-beam system to deliver 1 KJ in one nanosecond is under construction.

+) Composed from records of oral presentation 3 The following results have teen obtained wit e LEKKhth O systems Anomalous heatin parametrio t e gdu c instability has been clarifiede Th . threshold laser power intensity for this process is 101Q W/cm2* Below .the threshol e expansiodth s nthermai l powewhica s hha r dependenc f fto e4 /9, where Q is the incident laser flux. Above the threshold the expansion is flux-limited which shows a power dependence of Q£/3, A control technique of oscillating line double-lasey sb r cavity wit hsaturabla e absorbe bees ha rn accomplished* The pressure broadening coefficien e CC>th 2 f la-seo t r lin s ederivei d froe mth small signal gain dependenc lase n pressurs eo ga r e using 5 atmosphere pressure E-beam C(>2 laser* a 3 LASER FUSION RESEARCH AT THE LEBEHEV INSTITUTE OP PHYSICS, USSR ACAIEMST OP SCIENCES V. Gribkov

Basov'n I s Laborator e Lebedeth f yo v Institut e probleeth f mo thermonuclear fusio lasey nb s seei r s consistinna followinge th f go :

I* Creatio optiman a f no l laser-target system ensurin gmaximua m amplification coefficient: V

Developmen. II preparatiod tan targete th f no . This must ensure high average density in the final cumulation state: 10 -f-10 g/cm , and hav largea e initial fuel mass (DP, CUT, LigDP): 10. g ~ ,-2

III. Achievement of a maximum oonyers ion coe f fioient from laser energy to kinetic energy of the collapsing material:

IV. Creation of such cumulation dynamics that the density and temperature profiles before the beginning of combustion are as follows:

TkeV

I02ll0 10

i• 10

. ObtaininV g stabilit compressioe th f yo n process* 5 H.Gn I . Basov*s Laboratory these problem beine ar s g solvee th n di following way: . I Powerful lasers neodymiun O ) (a m glass (1) A 9-channel device has been operating since 1971 , , contrasJ ns T0 , 1 a&10 a 50 (0 E a 1 t rad) (2) In 1974 a 20-channel laser device was started up. ; kJ 2 T J k J 41 0 20 (Ea T a 2 x 10"11 s r 10~9 s f 2 x 108 s, contras 1x 0 , 0 3 1 $ta rad) 216-channe(3A ) l devic s beini e g built which will be started up at the end of 1976, though one quarte f 197ro wil d 5operatine en b l e th y gb (E = 10 kJ, T a 1 ns, luminosity 1017 W/cm2 sterad). (b) iodinn Thera s ns)i e1 a lase. T , rJ operatin0 13 a E g( f 197 o e energd 5Towardth en ye wilth s l increaso et 500 J. (c) A high-pressure C0_-laser is operating (p a 10 W/cm ). chemica(dA ) l lase s beini r g developed (?« + Hg).

II. In conjunction with Isakov's Laboratory solid and hollow targets have been developed and are being made; they are 50-2000 jun diameten i consisd an r f hydrogeno t , polymers, glas metallid san c oxides that meee requirementth t s impose targetn o d r lasefo s r thermonuclear fusion. co-operation I ) (a Ill,n TITwit e Institut. hth f Applieeo d Mathematic typ w f targeo ene s beea s ha tn developed which give amplification a s n coefficien -IQr0 t1 Ka for E. a 10-10 J in a simple (unprofiled) pulse; (b) In collaboration with Silin's department work is proceeding on the theoretical aspects of the conversion coefficient (absorption, reflectioe th f no laser radiation in the corona, heat conductivity, gas dynamics, etc.); method numbew A ne f ) o sr(c have been develope r researcdfo h on laser plasma (interferometry, multichannel X-ray

6 research, stud f reflectionyo , scattering, harmonics generation, HP-neutron diagnostics, X-ray spectroscopy, camera obscura, etc.); processee Th ) f absorptio(d o s harmonicd nan s generation, reflection distributioe th , n function, X-ray anisotropy, etc. have been studied 30-folA . d compressioe th f o n target nucleu achieveds wa s ; ) e WitC0_-laser (e e helth hth f po , experiment heatinn o s g beine ar g carried out, plasma densit temperaturd yan e have been studie mode-lockina d dan g typ f workino e g regime with the plasma has been discovered.

V. It has been shown that since the particle lives in the,possible instability ver a zon r y fo eshor t time (far shorter thae nth acceleration time), stable working regimes are possible in targets with thin sheaths. Apart from this e FLORth , A devic (togethep u s bee t eha nse r with Isakov's Laborator Filippov'd yan s Laborator Kurohatoe th f y(o v Institute theora d f an )combiney o d plasma heating witha laser and a relativistic electron beam is being developed (with Silin's department).

In A.M. Prokhorov's Laboratory collaboration i , n with Koval'skij, Pergament of the Kurchatov Institutes

I. (a) A 3-channel laser on glass blocks with a rectangular cross-section has been started up (E up to 1 kJ, T= 10~10-10~8 s, $o 2 x 10""4 rad)j UMI-3e Th 5) devic(b s undei e r constructio, kJ 0 =1 B n( X= 1.06; 0.53 !*)• Start-u s pplannei e th r dfo e beginninen th f 197 do r o 6 f 1977go | (c) Modules are being developed for a CO^-laser with a planned Tenergd •ns1 an f 1—.J yo k 3 ) Theoretica(a Ill, IV. V , l wor s beini k g done atthe Kurchatov Instn o . complex targets and stability. (b) Experimental work on absorption, harmonics generation, spontaneous magnetic field measurement, time dependence of X—rays. ) Ne(c w diagnostic method e beinar s g developed: image converter visible th X-rad n i s ean y ranges, holograph interferometry, etc. Thus, farther progress lies with the completion of construction of the above-mentioned powerful neodymium, CO-, iodin chemicad ean l lasers.

8 LASER FUSION RESEARCH AT LOS ALAMOS Gene H. McCall Los Alamos Scientific Laboratory Universit Californif yo a Los Alamos, New Mexico 87544 United States of America

Although the progress and current status of laser fusion research can bes describee tb resulte th y db Interactiof s o n experiments* these experiments are closely related to the lasers used to produce the plasmas being

studied. At Los Alamos the primary emphasis 1s on C02 lasers, but target

experiments are being done with both Nd:Glass and C02 lasers. The use of both types of laser gives a direct comparison of experiments done at different wavelength powerd san lasere Th . s currently operatind gan planned are: Nd:G1ass I. 2-beams 300 GVI 100-400 ps pulse A. 80 percent of energy 1n 250 yrad B. 100 percent of energy 1n 875 yrad C. Easily extended to 4-beams II. I-beam 500 GW 30-50 ps pulse A. Used for diagnostic Instrument development co2 pulss n 5 e1. W G 0 10 I. I-beam A. Operating for absorption and heating experiments II. 2-beam * 1 TW 1.5 ns pulse • . UndeA r constructio nean- r completion III. 8-beam * 10 TW . UndeA r construction IV. 6-beam * 10W 0T . PreliminarA y design 9 Early Nd:Glass laser target experiments on plane targets at Los Alamos and elsewhere showed that x-ray spectra from these targets could not be describe singla y b d e exponential dependenc f Intensiteo photon yo n energy. It was postulated that the electron distribution which produced this spectrum was nonthermal. Calculations done at Hvermore showed that the general spectral shape coul producee db velocita y b d y distributio fore th m f no exp(-o v/v0) where a 1s an adjustable parameter. It was not possible, however, reproduco t measuree eth d Intensity. Recent experiment Navae th lt sa Researc h Laboratory have confirme measuremente th d . Calculation r plasmasfo s generated,

bC0ya 2 laser gave better agreement Ifself-generatea d magnetic fiels wa d assumed. It shoul emphasizee db d that these measurements were Integrated over both time and space. It 1s possible, therefore, that the apparent non- Maxwell 1an electron distribution 1s only the superposition of Maxwell 1an distributions different ,a t temperatures, which exis different ta t times and at different places in the plasma. Calculations based on this hypothesis have been done by Winsor and Colombant at NRL and by Malone at Los Alamos, and 1t was found that the data Is consistent with this assumption 1f a mechanism exist r limitinsfo electroe th g n flux froabsorptioe mth n region to the Interior of the plasma. In the NRL calculation a self-consistent magnetic field limited the flux and 1n the Los Alamos calculation an arbitrary flux limit, whic turbulenceo t he couldu e db s used ,wa . Figur showe1 smeasuremena anisotrope th f to plasmf yo a expansion when thia n fil cellulosf mo e acetat targeta uses es wa datde a Th a. showe nar oscilloscope traces from Ion t1me-of-flight detectors located alon normae gth l targete toth uppee Th . r trac targee fros th side 1 mth f teo toware dth lowee laserth rd ,tracan fros detectoe 1 mth r behin targete n dth ca t I . be seen that for target thicknesses between 400 A and 1600 A the signal does not change much in front, but the Ions at the rear are much slower for the thicker target. Calculations base classican do l conductivity giv almosn ea t 10 isotroplc expansion for the thickest film In this experiment. Thus, a reductio conductivitn n1 Indicateds y1 Shat ,Livermort bu y a shows eha n thae tth transverse conductivit reducn y ca effectiv e eth e Intensit spreadiny yb e gth energy over a region larger than the laser spot size. Even with this effect, however, a flux limit Is required to explain the data. In general, the experiment distinguist no o sd h amon modele gth s which have been Investigated. A consequence of a hot electron distribution and a cold 1on distribution 1n the absorption region 1s the electrostatic acceleration of Ions by the electric field generated by the hot electrons. Using the description of Mors Nlelsond ean finde , on energ n s 1o tha e y tth depend lasen so r Intensits ya

E, * I2/3 Figure 2 shows the measured ion kinetic energy as a function of laser Intensity

fo polyethylenra e target illuminate C0a 2y b dlaser Ie 'Th . dependencs e1 seen to hold. Another consequence Is that the energy per unit charge should be a constant. Figure 3 shows an ion spectrum measured in a NdrGlass laser experiment which produced a rather cold plasma. The assumption of constant appearZ justifiedE/ e b o st . Neutrons can be produced 1n the corona if Ions with sufficient velocity pass through cold material whic ablates i h d lasee earlth rn yi pulsef I . characterizee on 1oe snth expansio kinetiy b n c numbe n energio d ry an usin g th 'eI dependence2/3 possibls 1 t ,i calculato et neutroe eth n yiel thesn i d e experiments. Figure 4 shows such a calculation for the experiments of Yamanak Flouxd aan agreemene Th . t i sgooe b see do nt ove rdecada e in laser o decadetw flu d neutron xan si n yield. Much of the information on the spatial distribution of energy 1n Implosion experiments has been obtained by Imaging the soft x-rays emitted by glass microballoon targets. Figure 5 shows the result from this type of experiment. glase Th s microballoo mountes nwa thia n no d plasti s illuminatecwa foid an l d by two beams at an intensity of 3 x 101 5 W/cm2 . The upper photographs show the data, the center traces are densltometer traces of the photographs, and 11 the lower figure show targete sth . Neutron yields from these targete b n sca observed from eithe "weake rth "strongr "o " Implosions. The Interpretation of these photographs 1s not simple because they are Integrated over tim wavelengthd ean obtaio T . n sufficient intensity, x-rays radiatiousede e mosar th t V ,f bu t o ke n3 betwee id s an compose n1 f linedo s and free-bound emission, and a simple Interpretation of filtered channels is not possible. Figure 6 1s an x-ray spectrum of silicon measured in an experimen ywhic0 n mti 10 diameteha r glass shel o beams heatetw wa l sy db fro Nd:61asma s laser complicatee Th . d spectrum clearly show freee sth - bound continuu d Indicateman neee r botth sfo d h spatia wavelengtd an l h resolution if one wishes to derive the spatial dependence of electron temperature from these measurements. By placing a narrow slit 1n front of a KAP crystal spectrometer one can obtain such information. Figure 7 shows such a measurement. The upper densitometer trace shows the spatial dependence p of the Is - Is2p resonance line in heliumllke silicon and the lower trace shows the spatial variation of the Lyman-ct line In hydrogenlike silicon. Spatial resolution is approximately 50 ym. From the ratio of the lines It can be seen that the center of the shell is at much higher temperature than the outside. Neutron emission from these target bees sha n obtaine severat a d l laboratories, but, in general, the conditions under which neutrons have been obtained are not relevant for laser fusion. For the small yields which have been obtained (106 -1 0 7) the dependence of yield on temperature is much stronger than the dependence on density. In these experiments the is s ga expense heateT th D t densitda f eo y such that compressioe th o nt required densit r laseyfo r fusion woul impossible b d e even If more laser power were available. It should be emphasized that the central problem of laser fusion obtainin e isth f higheatine go th h densitt thf go no e d yan fuel. Even curren e ith n t experiments, however beet no ,ns ishowha t n thaemittine tth g sourc thermals ei . Onl energn y1o ~ f my1 o J neae rth 12 pea reactioT kD energe th nf y o cross section woul requiree b d produco t d e observee th d yield. Becaus nonthermae th f eo l processes know occuo nt r In laser-produced plasmas possibilite ,th neutrof yo n productio thesy nb e processes shoul Investigatee b d d more carefullycleart no s 1 , t howeverI . , that the results would be applicable to experiments which more closely approximat conditione eth s require r lasefo d r fusion It sI .suggested , therefore, that more effor appliee Investigatioe tb th o t d processef no s which occur at density-temperature combinations necessary for laser fusion.

13 1600A 599 25° 2V 7.2%trans 205° 200ns 6.5 J

1400 A 603 25° 2V 9.6%trans 205° 200ns 22 J

360 A V 54.32 ° %25 tranB 7 s 57 205° 200ns 16.6J

Fig time-of-f1ighn .Io 1. t trace r thisfo n plastic films Illuminated pulss p 0 e3 bfroya mNd:Glasa s laser. Upper trac lases e1 r side, lower reatract a targetf ro s e 1 . Target thickness In Angstroms. 14 200 I T I I i

105 0

I t I t I I I t 10 I I . ..I I 1 10' I0i3 I014 1015

Loser Flux I (W/cm, 2)

Fig. 2. Kinetic energy of H + ions emitted from a CH target illuminated 2

by a C02 laser as a function of laser intensity. Pulse width is 1.5 ns. I I i r

+ <0 «* 10 x o o o o a < • evi

0) O ^

N \ oo111

I I i i I — IO O O 10 CM • ro — o 3 5 AP/NP

spectrun Io Fig . .3 m fro CHma 2 plasma illuminate Nd:Glasa y b d s laser.

16 10'

(a) (b)

3 Q>

A Yamanaka (ref I )

• Flou alt .e x(re f I)

10 i i i i_____i 6 8 10 20 40 60 Laser Energy (J )

Fig. 4. Comparison of experimental and theoretical results for corona neutrons.

17 3» 1 * *

Strong implosion Weak implosion

X-ray pinhole photograp f laser-driveho n implosions

y » K •

Fig. X-ra5 . y pinhole photographs fro mglasa s mlcroballoon illuminated btwo-beaya m Nd:Glass laser. 18 Fig. 6. X-ray spectrum generated by a glass microballoon target. Dispersive elemen EDDn a Ts ti crystal .

19 8/15/75-1 Silicon KAP xstl Heliumlike 50yam slit Resonance 90/tm balloon

Hydrogen like

Fig. 7. Spatially resolved x-ray line spectrum of silicon. Spatial resolutio approximatels 1 n ym0 y5 .

20 REVIEW OF ERDft. INERTIAL CONFINEMENT FUSION EFFORTS G. W. Kuswa ERM, Washington D»C.

The goal of the ERM inertial confinement program is to produce thermonuclear 'bur smaln ni l pellet develod san p applications. Main-line efforts beine ar g directe achievo dt e pellet implosions with neodymium glass lasers, C0 lasers, and electron beams. Various schemes for employing ion beams

are2 also under study because of the favorable energy deposition properties of ions, which exhibit maximum dE/dtheif o d xr en nea rangee rth . examinatioy b e se grape n th ca hf no beloe spendinOn e wth g distribution amon varioue gth s funding categories. Hot resule showrecena th f s tno i t decision to double support for diagnostics to accomodate new requirements and ideas brought currenttarge e abouth y tb t interaction experiments. A balanced national effort takes advantag followinge th f eo :

LASER-FUSION PROGRAM ELEMENTS FY 1974-76

19*. NCWIASERS

IS'. EmilMM'S ir. mur O£S;CM 2*. SYSTEMS STUDIES S DIAGNOSTICS 1 1. ELECTRON «AM

S'. C02 USERS

23*. NifcGlJlSS LASER

J5 FISCAL YEARS

I» Utilizatio Uniquf no e ERBA Laboratory Expertise (Primaril LASLt ya , Sandia, LLL) ove- year0 r2 s experience with TN burn experimenta- l diagnostics base managemen- largf to e applied scienc researcd ean developmend han t edeavour - large computers sophisticate- d codes Utilizatio. II industriaf no universitd lan y expertise - laser and optical development mor- e ideas stimulate incorporated dan d - industrial research capability fabricatio- n technolog hardwarr yfo diagnosticd ean s III* Development of Capability that Extends Program - development of pool of trained experts preparatio- partnershiy nb industriar pfo l takeover when commercial implementation becomes feasible. 21 The inertial confinement program office at EEDA is planning on funding abou externa0 t7 l contracts durin fiscae gth l year 197 orden 6i implemeno rt t the philosophy outlined. The major program goals and milestones are outlined in the figure below but one should bear in mind that the program is under continuing review and the

INPUT f BOM MAGNETIC CONFINEMENT PHOODAM

EXPERIMENTAL POWER REACTOR SUPPORTING LASER RESEARCH. DEVELOPMENT AND ENGINEERING ______INK GLASSJiASER FACILITY I

1UU KIWJQUL , LASEECO R FACILITY

HIOMtNtBGY GAS LAStR FACILITI Y NEUTRONS., X-RAYS I OPERATIONAL TEST SYSTEM

ADVANCED FUSION FACILITY

MILITARY APPLICATIONS

£ BEAM FUSION FACILITY

SUPPORTING E BEAM RESEARCH. DEVELOPMENT AND ENGINEERING

CALENDAR YEAR more distant project dated ssubjecan e sar changeo tt * New laser development is require eventuar dfo l commercial power production becaus expectes i t ei d that pellet gains of "100 will be optimal for reactor design, (Preliminary system studies show advantage producinr sfo g high frequenc smalf yo l pellet explosions rather than a lower rate of larger explosion). Gain including the laser efficienc pelled yan t gai grap e shows ni th hn n o belo w plotted against a multiplication factor for fission blankets of various kinds. The slauted straigt lines show base% recirculatin 0 d10 d an , g25 power, 10 f so upon all internal energy need to run the inertial confinement plant. The curv shows ei n through points which correspon estimateo dt ! requirements for stage fusiof so n plant design presend ,an projecter to d laser development are also shown. Electron beam efficiencies are presently such that the range labeled "new lasers equally "ma y well refe electroo rt n beam technology.

ENRICHED NATURAL ENRICHED BLANKET TYPE DEPLETED URANIUM

COMMERCIAL EQUIV

III I RECinCULATINQ POWER

10% 25% IOCS (BREAKEVEN)

OXYQEN 1992 PROTOTYPE '•»,» J LASER COMMERCIAL HYOfllO . "X- 11 POWER PLANT

I, HF LASERS DEMONSTRATION YOHIO POWER ^ I P ' 1982 ENOINEERINQ x 1986 BREAKEVEN . RESEARCH FACILI DEMONSTRATION POWER PLANT

0 2 30 0 1 40 SO BLANKET ENERGY MULTIPLICATION

22 Glass systems Despite difficulties with glass laser systems they are in the most refined state of engineering and are currently the work-horses of laser fusion experiments mose .Th t important measur lasea f powees o ri targetn ro . Power is limited by the tendency for glass to exhibit non-linear properties at high intensity levels. This results in the break up of the beam into filament higf so h intensit divergenced yan , whic causn hca beaea havo mt e targeitn sow t power minimize peat da k laser power. Careful attentioo nt lase rspatiaf o desig e us l n e filtering sucth s ha ) improved glass with high gain and lower non-linear index, and design of focusing optics to minimize glass lengt requirede har . Pulse shapin importans gi manr tfo y pellet designs. Means for producing nearly any desired pulse shape from a given oscillator pulse have been develope modt dbu e locked oscillator produco st originae eth l pulse presentle ar reliabls a t y no desireds ea . Effective isolatio laserf no s from damaging back-scattered light and isolation of the target from fluorescence of the laser or unwanted preccursor pulses from the oscillator is very important. Presently, experiments which produce neutrons are critically dependent upon minimizing prepulses.

Gas lasers Gas lasers are superior in principle to solid state lasers because mediupossibldamagt e no th s o mi eparameterd t ean readiln sca changede yb . Presently the OOp is the farthest developed and a one nonosecond 100 kiloioules facilit planneds yi . Developmen multilinef to s oscillators, needer dfo efficient energy extractio pulsen ni s shorter tha relaxatioe nth n time between adjacent laser levels, has shown that this can be accomplished, but reliability is stil mt goolno d as required. Isolators for keeping prepulses from targets must als perfectee ob C0r dlasersfo , which hav broaea d spectral outpue tdu

to multiline operation2 .

Electron Beams Electron beam technology can currently deliver energy stored in capacitors to electron beams with efficiencie thi d %0 t3 an s f focusesenerge o b n yca d onto targets and absorbed with up to 50 % efficiency. However, e-beam targets require walls sufficiently heavy 1>o stop electrons, Appartently the only neutron producing shots employ fast rising pulses, for which plasma clouds surroundin pellete gth smalle sar . This permits electron cloud exiso st t durin lasee gth r burst sucd ,an h cloud acceleraty sma e ions to energies sufficient to explain a large share of neutron production. Longer prepulses produce more extensive plasm neutrar ao l particle distributions which cannot suppor electrie tth c fields necessar acceleratinr yfo g particleo st neutron producing energies. More work remain settlo st e this important question. A large quantity of energy is required to drive e-beara pellets. Currently electron beam technology permits the study of energy deposition symmetry and material properties under shook conditions, and studies in these areas beine ar g actively pursued, primaril Sandit ya a Laboratories. The development of larger e-beam accelerators with shorter pulses of higher curren continuings ti majoe .Th r difficulty associated with scale up is delivery of the electrical power across the insulator which separates vacuue th m regioe-beae th f nmo diode fro transmissioe mth n line. 5Po accomodate large power flodiode wth e insulators mus made tb e larged ran the diode electrodes must also be made larger to minimize the inductance of the system. In such large diodes it may be more difficult to control the accurac risd yan e tim e-beaf eo m focussing bees ha n t .founI d experimentally and theoretically that plasmas and ions formed on the diode surfaces profoundly influence the e-beam dynamics* It may be possible to control the beam by 23 artificial introductio plasmaf no s int diode osomd th ean e encouraging progress "bees ha n mad thin ei s direction*

Diagnostics*

The e-bearo program relies heavil holn pi en yo X-ra y photograph o examint s e the uniformity of e-beam deposition on pellets* The most notable recent progress e applicatio bees th ha n ni f computeno r image enhancement techniquer fo s maximizin e informatiogth n froe data mth accompliso T . h this point spread holen pi functine obtaine se ar th f o sd usin X-.ran ga y sourc f similaeo r energy e experimentth computee o t th d an , r program uses thi sunfoldine datth n ai g process* The same technique may be useful in the laser pin hole experiments* A means for obtaining flash X-ray pictures of imploding e-beam pellets using an auxiliary pulsed X-ray source has been employed and is being used to compare experiments with theoretical models of pellet dynamics* Other important diagnostics include doppler interferometr studo yt y rear surface breaku f half-pelletpo r slabso s , multipulse optical holographo yt examine plasma motion in diodes, and spectroecopic techniques to aid in further determining plasma properties* The laser program rellfea somewha n o s t different diagnostic base* Studf yo reflected and scattered light from pellets at the input wavelength and its harmonics allowlearo t e non s abou lighe th t t absorption propertie outee th rn i s regions pelletse oth f * Streak camera usee ar srecoro dt time dth e dependenc f thio e s light* Improvemen f streao t k camera performanc reliabilitd an e importann a s yi t activity in the program* Currentl devleopmene yth f grazino t g incidence X-ray optic s beini s g carried out to improve the collection efficiency in X-ray imaging by a factor of 10 holn ove pi f equivalen eo a r t resolving power. microe Resolutioon ne th n ni rang s anticipateei d with sufficient sensitivit alloo yt w streak camera recording of X-rays produced during the pellet implosion* A new streak camera development will probably resul

Neutron detectio s importantni t presenbu , t neutron yielde sar insufficient to get accurate information on the HF temperature* Consequently heavy reliance is now being placed on alpha energy measurements from the Iff reaction* One factor which may not be completely known presently is the effect of the pellet wall at elevated temperatures on the alpha energies* Stopping power measurement of thin films heated by laser pulses may be desirable* The large quantity of data generated, not only by the pellet, but also by the laser or e-beam accelerator on each shot places an unmanageable burden on the investigators* Consequently there has bee nsteada f on-lino ye increasus e e computerth n eo r datfo s a reduction refinemene *Th f interfaceo t s between diagnostice th d san compute s beini r g pursue largee th n do r experiments*

24 Pellets. The design of pellets is too complicated to summarize and is carried out primarily in the main ERD& laboratories. The theoretical developments are placing increasingly more difficult burden fabricatorsn so instancr *Fo e one result asks for pellet finishes as smooth as the interatomic distance knowmaterialt e ofno th ns i whethe t *I r this requiremen realistis ti n ci difficulte vieth f wo uniformln yi y illuminating pelletonle th y d san partially known effect of smoothing the implosion by electron thermal conductivity in the presence of self generated magnetic fields* Pellet selection and fabrication relies on a collection of innovative techniques, but we have been somewhat limited by relying primarily on available glass microspheres use fillinr dfo g plastip commercially* Work is under way to fabricate shells made of other materials* The technology producinf o g small liqui spherethem f ai dIf m d accuratelsan partls yi y in existance, and work is continuing in several laboratories to freeze uniform distribution inside th n Uf ePo so surfac glasf eo s microspheres* Conclusion* While there has been exceedingly rapid progress in inertial confinement, and several laboratories are producing neutrons, we must still remain cautious in our interpretations of the data* Several mechanisms have been suggested for producing populations of fast ions responsibl e whicb y hma producinr efo g neutrons shoult *I d also be emphasized that present experiment thoughe sar operato tt regima n ei e which starts on a rather high temperature adiabat so that the high compressions require higr dfo h gain obtainedt fusiono e nplasmar t ; ho fror afa m conditions required for thermonuclear ignition produces the neutrons* presene th f I t neutron truyieldf o ee thermonucleasar r originy ma e ,w still have to overcome problems of instability and mix of shell material before high gains become possible anticipation *I thesf no e possible problemt si woul desirable db mort pu e o eemphasit obtaininn so g high quality ditn ao stability, material breaku mixingassociated e pan th d ,an d theory*

25 LASER FUSION RESEARCH AT THE CENTRE D* ETUDES IE LIMEIL, FRANCE J.P. Babuel-Peyrissac and J*P* Watteau

The main results obtained at the Centre d Etudes de Limeil on laser interaction, implosio numericad nan l simulatio presentede nar * 1 Laser interaction at 1*06 /urn on solid Eg plane target was studied overange th r e 10*2 . 5.101* W cm lase r ~2Fo .r flux less than loHl.cnT2 absorption seems to be classical} from resonant absorption near the critical density, 2too light is emitted and permits the evaluation of the focus spot size* Above 101* W.cnT2 absorption becomes anomalou hard an sd X-raye sar observed with energies up to 2?0 fceV} this anomalous behaviour may be due Brillouie onsee th th f o to t n backseattering instability studo *e T yth interactio t highena s laser p fluxes0 r 10 callewa 1 a ,s 10 builtdP e th , last amplifier containing 80 mm disks. 10 J at the end of the laser and 6 J< at the target are obtained, but the disks are rapidly damaged by burning particles coming froe cladinmth g which absor ba grea e tflas th par f ho t lamp UV light* 12 2 At 10.6 witd /ur 1an n0hw fe fluxe soliW.ca n o f mo sd D , 2reflectio n is of the order of 60$, ICX being reflected inside the focusing lens solid angle fasd an t, ions detected. QUATOn I R implosion experiments r Ao l 2 holloCH , w cylinders were Ns d 3n glasilluminate - J s 0 foue laseth 50 r y e rdb beam th C£*Th f o s e diamete thicknesd an re cylinder th f o s s vary respectively from 200/uro nt 1 mm and from 25 /urn to 100 /urn, and laser flux is up to loM W.cfir2 . From visible light pictures,' interferrograms at 0*53 /urn and ions collectors, e ablateth d corona, plasma expands symmetrically when'the beam e defocusear s d and overlaps the transit time of the induced shock through the tube wall thicknes itd ssan tim convergo et axise th e deduce n ar ,o e d frodynamicae mth l behaviou plasme th f o ar expanding insid tube eth e froe innemth r wall towards axise visible th Th . e light emitte thiy db s plasmattenuatioe th r o a a f no coxial 0*53 /urn laser beam are rewided along a diameter by a streak camera* From the transit time and knowing the equation of state for the cylinder' material, pressure was evaluated to be of the order of 2 Mbar* The average velocit expandine th f yo g plasm s 5*10i a s"m 1°c which , accordin numericao gt l simulation should correspond for Al with a density compression ratio of 10 on the axis. We are now preparing spherical implosion experiments by putting a 90 ram diamete amplified ro r e las mn fron4 th i mr6 t f diameteo t n eaci d h ro rbeam * The energy of the Cg laser is increased by a factor of 2 with the pulse duration remaining the same. The four beams are synchronized on target with an accuracy of 50 ps, each beam delivering about 150 J in a repeated way at that time firse Th .t integrated X-rays pinhol yu0 e mpicture15 diametee th f o s r CH2 spheres held by 10 /urn diameter supports show that these supports absorb e laseth par f ro t energ perturd yan e implosiobth n which longeio sn r symmetrical* The supports must be changed to a few yum diameter* The implosion is studied analytically and numerically* For isotropic and homogeneous compression pressur lased ean r power law e foun ar ss similarit a d y laws which help improvin e efficiencgth f numericao y l simulatio r preparinno g experiment s• fluidUsino dimensionae tw gon a s l code, implosion f sphereo s r o s shell CHn i n Us2i r Po were simulate r differendfo t laser pulse shapes

27 (step, ramps, gaussian, Nuckoll'» J 0 senergn 10 a law w d a.f fe )yo an For spheres it is necessary to deliver an important part of the laser energy in a short time at the end of the implosion to obtain high pr product* For long pulses the efficiency is best for shells when mass is fixed, but the final density and temperature depend greatly on the pulse shape, e.g Nuckoll'e .th exponentw sla Ar l*Fo shell s filled with ln U£To optiman a s ga l thicknes founs s i whic r absorbede fo hth d energ wels yi l transferre withous dga froe shele tth m th excessivel o lt y increasing its enthropy* Finall orden yi optimizo rt coupline Cee th g th lase f targetsgd o ran , numerical simulations are done with the hypothesis that only half of the laser energy is absorbed /tu0 n15 diameter *Fo r CH2 sphere absorbeJ 0 ,15 d Gan0 Wd 18 maximu m powe average rth e density compression ratio

(with respecsolie th do t t densitaverag e th d yean J temperatur"8 o )s i eT eV9 1 * s Whe i maximue nth mgaussiae poweth , increases rGW i n 0 puls33 o det duration being 500 ps, £/& and T are respectively 18 and 74 eV for a 80 /tun diameter sphere absorbing 94 J» In this last case, with a 10 GW-3ns prepulse aAr rfo aspec»5 } 30 o tgoet ratip su o shell havin same gth e mass, attainee ar V e maximu d d0 an 71 , d meV an value 0 9 6 14 f d so an 4 4 e anar dT harcentee e th th d f n rcoreo i .

28 LASER FUSION RESEARCH IN THE UNITED KINGDOM I. J. Spalding UKAEA Culhatn Laboratory

There is no laser-compression experiment sb the UKAEA Culham Laboratory. There is, however, a very active interest in the laser-heating of plasma for filling toroidal magnetic-confinement devices, and in the diagnostics of dense plasmas widA . e rang relatef eo d laser work lower ,fo r density diagnostics and other applications, is also undertaken within the Laboratory; longer-term exploratory wor supportes ki Culhay db nint ma universitiesK eU presene Th . t performance somf so e typical Culham facilitie listee sar d below. (Projected performance is indicated in parantheses)

LASER WAVELENGTH ENERGY POWER MODE APPLICATION (J) GW STRUCTURE

13 3 1. C H5F 496 - 3xlO- Multi Tokamak diagnostics it tt (0.3) (3*10~3) (single) n it

2. C02 10.6 i 1 single Heating/Diagnostics n tt 150 2 multi Heating tt n (1000) (1-200) (single) Heating it it large 10"* (continuous) Industrial 3. Nd/glass 1.06 (100) single High density diagnostics k. Nd:POCl3 1.052 . 50-60 3 multi Heating

seey Itma m strang mentioo et (continuousna k0 )W1 laselaser-fusioa n ri n context, but design experience with higher mean power systems of this type helps one to appreciate the technological challenge of laser-fusion; I will reserve commen somn to e implication usinf so g multi-shell cryogenic target reactoa n si r environment until the reactor session on Friday. The laser-heating programme (Spalding and co-workers) forms part of a co- operative Euratom venture ; Culham is initially using a 160 litre-atmosphere electron-beam preionized C02 lase thir rfo s work, which wil discussee lb n di detai Wednesdayn lo . Recent work includes laser-induced acceleratio pelletf no s to velocities of 10*-10s cm/sec (for refuelling investigations), computer-modelling of CO- laser pulse-propagation (2), and an experimental investigation of density- cavity ('caviton) formation at incident COp laser intensities of order 10l3W/cn? . A very important objective of the programme is the optimization of the energy transfer between lase targed ran problea t- m whic closels hi y relate nono t d - 29 linear coronal interaction physics of current interest in laser-compression experiments, describe othey db r worker thit sa s meeting. The high-density spectroscopic investigations at Culham are being conducted by Peacoc colleaguesd kan primarA . y objectiv thif eo sobtaio wort s ki na quantitative fit between x-ray measurements (*0 and two-dimensional MHD computa- tions of the general type discussed in Reference 5- I. J. Spalding References 1. 'The present state of research into Plasma Heating and Injection Methods'. Euratom Report EOR FU ?k/A.GEI 10/R1 Section 5(c). 2. 'Pulse propagation in CO- laser amplifiers' Armandill publishee b Spaldind o t an PhyJ , oE Appn , J sdi D gI l Phys (Culham Report CLM-P*f23) 3- 'C(>2 laser-heating experiments' Donaldso alt e . P nT Proceeding Europeah 7t f so n Conferenc Controllen eo d Fusio Plasmn& a Physics, Lausanne, Switzerland (September 1-5 1975)• k. 'Spectral classifications in the Fe XIX to Fe XXIII isoelectronic sequences' Fawcett B C, Galanti M, Peacock N J, J Phys B Atom Mol Phys £, 11^9 (197*0 5. 'X-ray emission from laser-produce3 plasmas', C Christiansen J P, Peacock N J, and Galanti M, Lausanne Conference (Sept 1-5 1975).

30 Laser Research at the Institute of Applied Physics University of Berne (Switzerland) H. Weber

The Institute of Applied Physics includes three main activities: Microwaves (Prof. E. Schanda), fluorescence (Dr. T. Bin kert), and the laser group (Prof. H. Weber). In the fol lowing a brief review on the activities and facilities of the laser group will be given. The program and present status of the laser-plasma group will be presented in more detail.

In the summer 1963 the work in the laser field started with a few collaborators who organized the International Symposium on Laser Physics and Applications in Berne in 1964* Toda e laseth y r group consist abouf o s scien0 3 t - tific members including Ph.D.* students and technicians. Investigation e laseth rn si fiel carriee n i dar t ou d close contact with several industrial companies. There- for activitiee eth e laseth rf o s dividee groub y pma d into basic research and applied research. This parti- vera t y no tiostron s i n g one, because thes fieldo etw s are closely connected and stimulate each other. The laser group has become one of the laser centers in Switzerland. Thus laboratorr ,ou constantls i y y con- fronted with many problems concerning laser applications. As it is impossible to treat all these problems within an university laboratory Appliee ,th d Physics Institute in collaboration with some Swiss industrial Companies have founded the LASAG Inc., an organization which studies practical laser applications on a commercial ba- sis in consultation with the Institute of Applied Phy- sics.

Application of holography and interf erometric techniques on quality control, developmen holographif o t c methods plasmr fo a diagnostics. 31 GaAs-diodes for range meters, mode- locking, single frequency diodes, technology of diode preparation*

cw-Argon (100 W) and Mercury systems, CO,, laser with mode-controlled output for material processing and plas ma generation.

Nd-YA C0d 2Gan laser interaction with metal. Investiga- tion of optimum parameters for material processing with moderate laser systems (lO 10- 7 9 W/cm2, V* 10~ 10~- 6 8s).

Mode- locked dye lasers for plasma diagnostics, modulatio laserf no s (periodic Q- switch) . Satellite ranging and illumination.

Interactio picoseconf no d pulses with matter, investigation of reflectivity, absorption, and plasma instabilities. The laser interactioe systeth r mfo undes ni r construc- tiowild finishenan e l b d this year hope . W star o et t with the plasma investigations at the end of this year.

Mode-locked ring oscillator with Nd-YAG rod. Stable re- sonator configuration (resonato insensitivs ri diso et - turbance by thermal effects of the rod) . Emission of a very reproducible mode-locked pulse train, Gaussian shap timen ei , frequency spectruffi.Thd ,an e puls bans ei d width limited, V ** 35 psec. The spatial structure is monitored by an array. Single pulse selection by KD* P electro-optical switch, improving the signal to noise ratio by a discrimination amplifier. Powe energd ran y amplificatio Nd-YAy nb G 32 preamplifie ND-Glaso tw d ran s amplifiers thosf o e e,on is under construction. The output energ abous yi t 0.1 momente Joulth t ea t ,a thif o hop e sd w achievo een t e th Joulee1 .

JDiagnostic^Tools^and^yacuum^Chamber At our disposal are fast streak camera (Hadland) fast X-ray diode X-ra Bragy- g spectrometer ion collector «o vacuum chamber (10 Torr) A grating spectrometeX0 regio10 e undes th ni r rrfo construction.

N dYA- G / Glas s Laser Syste] J psec5 3 [3 - m1 ,

Oscitlator KD*P Discrimination Amplifier el. opt. Switch /- Dye

Nd-YAG

Faraday Rotator Amplifier__s I I _ vr«"^v > •» •W •«Ti _PtrL _ ^p]> Nd-GlasI s apodized aperture Vacuum chamber

Fig. 1 Nd-YAG - Glass laser system for generation and investigatio plasmasf no . NATIONA LABORATORD LAN Y REPORTS

Electron-beam produced fusion RESEARCH AT THE I.V. KURCHATOV INSTITUTE OP ATOMIC ENERGY POWERFUF ONO THB BUS L ELECTRON mu INITIATO sT E A PULSED THERMONUCLEAR REACTION L.I. Rudakov

In view of the relatively high penetrating capacity of electronSf thick sheaths (0.1-0. leaf Me 3 o copper Vd1- o m 3 m electrons r rfo requiree )ar r dfo stopping them. Ignitio thermonucleaa f no r reaction requires acceleratiof no the sheath containin heatind gan D-e Tgth mixtur velocita o et ove f km/s0 yo r15 . In order to utilize all the energy of the beam, of duration 50 ns, for the acceleration of the sheath, the initial radius of the target must therefore toe abou. Thescm t1 e conditions allow evaluatio targee masth e f th tso f sheath-no , (l-3 g), and of the energy required for its acceleration (10-20 Ml). When the D-T mixture is burnt in such a target, a thermonuclear energy of 10-10 J can be obtained. With the target dimensions quoted, the duration of beam action on the target corresponds to the range of pulse durations of existing accelerators. 7 quitIs ti e feasibl beae obtaio th me t n 10 x i orde energe n 'n2 a J th f ro f yo presene atth t stag technicaf eo l development. The pulsed thermonuclear reactor design developed by E.P. Velikhov, V.V. Chernukha et al. at the I.V. Kurchatov Institute of Atomic Energy [l] foresees introducing into a capsule construction injected into the reactor a massive screening sheat neutror hfo n absorptio retardationd nan , which would serve as the working body in the energy conversion cycle after evaporation. This permits a significant reduction of damage to and activation of the walls of the explosion chambe neutronsy rb prolongd ,an service sth chambeee lifth f eo o r t 20-30 years, which correspond usuae th lo s t standard electrin si c power plants. Asufficientlta y high explosion energ materiaye (^1th ) sucJ f 0lo h a heatesheate b n 10^°Ko dht ca , which permit highlf o e ysus effective thermodynamic cycles, e.g. the MED method of conversion, by which a power plant efficiency of 70-80$ can be obtained. An explosio containee b nn energca chambern J di abouf yo 0 t1 s witha diamete 20-3f ro weigha 0 d m500-100f ,an to 0 tj such chamber constructee b n sca d in the present state of technological development. Assuming that the energy conversion coefficient will be of the order of 10 —10 , initiation of such a fj thermonuclear explosion require energn s a electroe f th i?yo n 10i 'nJ beam. An accelerator of electrons with an energy of (2-3) x 10' J in the pulse an poweda (2-3f r^o 0 mighH 1 instanc r )x t fo e consis numbea f to f ro modules arranged around the vacuum chamber, as shown in Fig. 1, 37 Diagra pulsef mo d thermonuclear reactor with electron beam ignition. If an accelerator with a power of 3 x 101 2 W is selected as the individual module, 6O-100 modules will be required. The parameters of such a module would "be clos thoso et existinf eo g accelerators* Wit outpun ha t voltag totae ~Mf th 3 e o l currendevice th n eti shoule db know s ordei e o f th t n70-10 f I r o tha . diod0ta MA e current cannot exceeda certain critical value.

J a 104 £ Y,

where r is the cathode radius, d the anode-cathode separation, and Y the relativistic factor. module th d e an outlet m c closele 1 Whe sar a nd y packedA M ,currena 0 7 f to ca achievee nb d ove rradiua 5-1f s o . 0Thim s correspond requiremente th o st s explosioe th r fo n chamber. The construction of accelerators giving 10—17 08 J under pulsed conditions and trigge o theit e r us rpulse a d thermonuclear reaction requir solutioe eth f no a number of physical and technical problems. The technical problems include synchronization of multichannel switching, beam inlet into the explosion chamber, developmen outlef to t window shielding, foil exchang evolutior eo f no an anodeless procedure for introducing the beam through the opening with a suitable system of differential evacuation to maintain the vacuum in the diode.

The fundamental physical problems are transporting the beam to the centre vacuue th f mo chamber ove effective rdistanca th orde e d th 3-1 f an r o f e eo , 0 m irradiation of the thermonuclear target. The problem of transporting the beam ma solvee yb usiny db gguidina g magnetic fiel admittind dan ints e gga o th chamber to produce a plasma tube for electrical and magnetic neutralization of the beam guidina [2] s .A g field ,cusa p configuratio fiela n- d frocoilo mtw s connecte explosiooppositioe n di usedth e b n n I targe.d ca nan n- t expansion stage this magneti cuse e HHD-conversior b fiel dfo n dca explosioe th f no n energy into electrical energy.

The modular design of the accelerator makes it possible to handle all the technical and a number of physical problems full scale on an individual module; in particular, it is possible to simulate irradiation of the target vacuu froe sidel th mal n msi chamber withi high-voltage nth e annular diode (a diagram of such an experiment is given in Fig. 2).

The proble producinf mo gpowerfua l beam transportinf ,o f o d an t gi irradiatin targee g th studie s Kurchatoe twa th t da v Institut specialle th n eo y 39 Fig . *2 Diagra diodf mo e simulating target irradiation fro sidesl mal .

Pig* 3. Diagram of Angara-1 device*

designed Angara-1 device (Fig. 3)» which is calculated for obtaining an electron beam with an energy of up to 2.5 MeV and a current of up to 400 kA for a period nsconsisto0 t f6 I . three—staga f so e single water line charge separata y db e air-type voltage pulse generator with an energy capacity of up to 150 kJ and a voltage of up to 2 MV. The Angara-1 device began operating in February 1975* Production of the necessary power density in the beam on entry into the explosion chamber requires increased electrical stabilit linee th .f yo 40 Experimental research on the efficiency of magnetic insulation was carried out on the "MS" accelerator. A voltage pulse with an amplitude of up to 400 kV was transferre acceleratine th o dt cathodp gga e acros ssectioa coaxiaf no l vacuum line. It was shown that with sufficiently high currents in the line an electric field density exceeding the breakdown value is reached in the line when the magnetic field itself exceeds a certain level. In gaps of 2 mm an electrical poweMV/c5 a d 2. rmo an t densitflo p u w f densit0 yo 1 tf/cs - wa mf yo recorded O numbena small-scalf ro e devices wit wavw hlo e resistanc formine th f eo g lines (Qohm)5 ~2. , self-focusing regime high-powef so r beam dioden si s were investigated. On the "Triton" device, the current density of the beam reached 5 MA/c/ m 2 with a total current of 200 kA. On the "Ural" accelerator a current density of up to 30 MA/cm was reached with a beam current of 90 kA and an energy flow densit1x 0 5 f W/cyo m C4]presentt A » , acceleratio thif no n films under the action of electron beams is being studied on the "Triton" device. The efficienc beaf yo m energy transfe sphericaa o rt l targe shows ta Fign ni .2 is being investigated on the "Ural" device.

In 197^-77 these experiments will be repeated on the Angara device at a level of 30-56 kJ, and in 197&-80 at 100-200 kJ. These experiments should yield information on the efficiency of the chosen system of initiating the pulsed thermonuclear reaction and on the appropriateness of building a multimodule devicenergn a r electroe 3-f yeo fo th 5 n Mi J n beam.

REFERENCES [l] VELIKHOV, B.P., GOItfHEV, V.S., CHBHHUKHA, V.V., At.Ehnerg. 3j54 (1974) 258. [2] BABYKOT, M.V., ZAVOJSKU, B.K., 3YATSTOV, A.A., HUDAKOV, L.I., Plasma Physics and Controlled nuclear Fusion Research, IAEA., Vienna, V. I, (l97l) 635. [3] GOKBESV, A.V., KOROIETT, V.D., SIDOROV, Yu.L., SMIRUOV, V.P., paper presented at Conference on electrostatic and electromagnetic plasma containmen relativistin o d tan c electron beams, New York, March 1974. [4] KOBA, Yu.V. et al., in: IABA-CN-33/F 2-1, Fifth International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Tokyo, Japan, 10-15 November 1974* 41 ELECTRON BEAM RESEARC SANDIT HA A LABORATORIESA ,US

G. Yonas

I. General Description of Program

Sandia Laboratories is engaged in an effort involving thirty scientists to investigate the feasibility of using intense electron beams to achieve inertial confinement fusion long-range Th . e goa thif lo s efforo t s ti demonstrate scientific breakeven durin earle gth y 1980's thio T .s endn ,a experimenta theoreticad lan l progra beins mi g followed includine gth development of electron accelerators of increasingly higher power. This approach is being considered as an alternate method to the use of lasers for ignitio fusiof no n reaction imploden si d pellet power sfo r production, becaus relativele th f eo y high efficiencies achieve e whicb n hca d with electron accelerator 50%)o t p .(u s majoe Th r technical questions whic beine har g consideres a e dar follows: deliver intensf yo ediameterm beamm w targeto fe st a ; f so efficient energy absorption; symmetr ablationf yo stabilitd ;an f yo spherically imploding shells. concepe Th usinf to g eithe beamo r tw onsr e o withi n accelerating diodes is being considered, using hollow cathodes and preformed anode plasma to provide charge neutralization. In order to minimize the distance of beam transport from the hollow cathodes to the target and maintain a low diode inductance necessars i t ,i maximizo yt breakdowe eth n strength

dielectrie ofth c interface through which energy reache vacuue sth m diode, and to increase the attainable electric fields in the vacuum- insulated section feedin emissioe gth n region goae thesTh f .lo e studies is to deliver ^ 10 W at 1 MeV from diodes of ^ 1 M radius. Target design studies employing ablator-pusher concepts indicate that 10-2a n i 0W nse 0 ct1 * unshaped pulse wil requiree lb achievo dt e 43 breakeven systemd ;an s analyses show that thit ,a s level powet ,ne r production could be achieved with an accelerator efficiency of 50% an hybrida d blanke purA t gaie. ^f fusio20 no n reactor would requir pelleea t leas t gaia implyin 0 f tnmor1 ) o (1 e neee r gth dfo complex target designs to lower the input power levels, or (2) if nature is benevolent, a non-classical electron deposition profile so that higher voltage electron beams can be used, or (3) the use of intense ion beams.

II. theoretical Program

A. Diode Physics; Multi-dimensional particle-in-cell simulation codes have been constructed in cylindrical, conical, and spherical geometries including electrode plasma, self-consistent electron and ion flows, self- consistent fields emissiod ,an n laws. These studies have showe nth importanc production io f eo predictinn ni g beam pinchin determininn i d gan g impedances and focusing; they also indicate that in certain cases the self-pinched electron beam can lead to ion currents equal to or even greater tha electroe nth n current. Sucbeamn hio s migh geometricalle tb y bean io m n fusioni e focuseus .r dfo

B. Fluid Modelst Solutions of fluid equations giving radial equilibria have been obtaine studo dt y focusing limitationd san condition symmetrf so targetsn yo . This work indicates% tha25 ta Variatio energn ni y flux shoul expectee db hemisphericaa n do l target slightly smaller than the beam, and a two-to-one variation on a target slightly larger than the beam*

C. Hydrodynamic Code Modeling of Target Response; A 2-D Eulerian hydrodynamic code including mixed phase equations of state, elastic- plastic effects, and fracture has been used to relate target response to beam parameters. Electron depositio treates ni d Monte-CarlusinD 2- ga o 44 treatment including effect magnetif so c fields. Prediction cratef so r formatio shocd nan k wave intensitie slan si b target implosiod san n characteristics of hemispherical and spherical targets indicate correla- tion with efficient classical absorption and symmetry levels as good as + 10%.

. TargeD t Design; Design studie performee sar d wit threeha - temperature, 1-D Lagrangian code including radiatio thermad nan l conduction. Calculations have included high-z shells (pushers) use compreso dt T sD gas with low-z ablators wels , a multipl s la e shell velocitr sfo y multi- lication. These studies indicate that breakeven should be possible at •»» 101 4 W with * 1 MeV electrons or * 10 MeV protons. The ion beam approach would allow roughly an order of magnitude reduction in the beam current and would permit the target to be injected into a vacuum

chamber as in laser fusion with no additional plasma required. Charge neutralization would be provided by cathode plasma electrons dragged by the non-relativistic ions int vacuue oth m region.

III. Experimental Program

A. Hydra: The Hydra accelerator uses a conventional Marx generator to charge two 80 nsec long, coaxial, water insulated transmission lines providing up to 0.8 MV, 0.4 MA, from each line. This accelerator can be singla use n di triggeree e lineb o bean tw smca e modth d r witeo h nsei5 » c jitte deliveo rt beam o singla r tw o st e target using curved, magnetically insulated, coaxial vacuum transmission lines. Recent experiments have emphasized shock response of slab targets, with holographic and other optical measurements of front and rear surface motion indicating classical deposition. Implosio velocitt n je tim d hemisphericaean f y o l targets absorbing 5-10 kJ have indicated 2:1 asymmetries in beam deposition. More diffuse beams have been used to implode spherical targets 45 wit k3 Jh 2- absorbe interferogramd dan ablatef so d material indicated symmetr goos +ya s da 10% . Experiments wit target. hCD s indicate neutron yields of 107 - 108 , thought to be a result of collectively accelerated ions. Future spherical implosion experiments are planned using pulsed flash x-ray shadowgrams, to correlate the implosion quality with time resolved neutron yields.

B. Proto-I: (Operational 1975) — The Proto-I accelerator which has recently been operated for the first time, is projected to deliver two 3.0 MeV, 400 kA, 24 nsec beams with two opposing cathodes to a targe commoa n ti n anode. This device uses twelv insulatel eoi d pulse forming lines Whic triggeree har d wit hswitca h jitte lesf ro s tha nsecn2 . The output current risetime of 10 nsec will permit studies of rapid beam pinching from cathodes of diameter up to 60 cm, using a preformed anode plasma. Froto- alsy Ima o permi generatioe tth severaf no l hundred kA ion beams which could be conveniently extracted through the cathodes grount (a d potential diagnosisr )fo .

C. Proto-II; (Operational 1976 EBFd )an A (propose d— operationa l 1979) Proto<-II initian ,a whicn i ls h i developmen t phase desigs ,ha n characteris- nse4 2 cMeV, 5 ticfroMA 1. , 3 f beamsmso o eactw f .ho This device employs sixteen pair untriggeref so d water insulated pulse forming lines in order to provide a power output of 8 x 101 2 W with a risetime of *> 10 nsec. Proto-II will test design concepts for use in a 4 x 101 3 W accelerator (EBFA) which has been proposed for completion in 1979 and should also permit the production of 108 - 10 9 neutrons per pulse in orde carro rt detailet you d studie fueT D lf so compressio heatind nan g by imploding shells. EBFA should be able to achieve significant thermonuclear yields. Wit furtheha greater o rW upgradr 0 (projecte1 o et d

earlfoe rth y 1980*s) scientific breakeve reachee e b th n f nca di technical obstacles mentioned are successfully overcome. 46 IV. Stannary — Electron Beam Fusion Research In summary, the Sandia emphasis for inertial confinement fusion is on use of a minimum number of accelerator modules and avoidance of beam transpor externan ti l fields. This approac consequenca s hi f eo numerical modeling as well as recent experimental demonstrations of beam self-focusing, efficient energy deposition, and beam symmetry on targets. They propos nsec0 pulseJ **e 1 • us 0 ,achievo 1 o s t et e breakeven with a fuel mass of 10- 4 g. Present experiments involve focusing of beams from two hollow cathodes onto a single pellet with studies of implosion symmetr stabilitd yan y using optica x-rad lan y techniques. Recently they have also suggested that self-focused electron beamy sma provide comparabl currentsn eio , permittin orden ga magnitudf ro e reductio requiren ni d current resula s sa improvef to d deposition characteristics. Soviee Th t Kurchatoeffore th f to v grou directes pi d toward beam transport in a plasma with an externally applied magnetic field. In this way they hope to make it possible to use a multiple module approach with relatively minor advances in high voltage accelerator technology. In addition, by transporting as many as twenty, 0.5 MJ^beams over a distanc severaf eo l meters, they envision survivable first walls with o fusion energy yields of * 10 J. Such values of pellet gain (100) are stated to be consistent with a pellet mass of ^ 1.0 gram and beam pulse duration of 50 - 100 nsec. Critical near-term experiments will involve ablation-driven acceleration of thin foil targets and studies of beam transport in cusp field geometries. Both group considerine sar g only collisional energy losn si depositio therns a bee thus r eha ns fa neither experimentar lno theoretical evidenc contrarye th o et ; both groups also expeco tt 14 operat facilitieW earle 0 e1 th yn si 1980' demonstrato st true eth e feasibilit thif yo s approach. 47 REB FUSION AT THE INSTITUTE OF PIASMA PHYSICS, Nagoya, Japan

A. Mohri

Experiments on the injection of REB into toroidal systems started in 1973f while ERA has been studied since 1970* For these experiments several electron beam sources are now in operations Phoebus-I (500 kV, 24 ns, 4*652), Marx generato MVthre 2 d kj( r1 ,an ) e small Marx generator J)0 s .24 (60 , 0kV The source Phoebus-I has an air-core step-up transformer with a high coupling factor and 4* is used for the beam injection into a toroidal device named SPAC-II* Marx generator (2M\T, IkJ) serves for experiments on ERA* Expeimental studies of the injection are summarized as follows* 1) A quescent equilibrium state of non-neutral beam ring could be realized when a relativistic electron beam (450 keV, 16 kA, 25 ns) is injected parallel to a toroidal magnetic field in a vacuum* The longest life time obtained was 20 ns which corresponds to 3000 revolutions of electrons around the torus. The electrostatic potential well was 1.1 x KTV. stabl2A ) e stat f neutraeo l beam rin mads gwa e whe e beainjectes nth mwa d into neutral hydrogen gas* The obtained ring current was 7 k*> and i* decayed with the time constant of 25 /us* 3) Injection and heating of tokamak plasma were tried* The tokamak plasma responded in a complicated manner* The heating efficiency was stout 5$ and part of the injected electrons continued to circuit around the torus without fast damping* With regard to future plans, a REB source of 10 kJ is to be constructed in e fiscath l year 1975* We have another J sourcplak 0 mako nt 5 eea withi yearsn2 * Using these larger sources, we will examine the interaction of REB with solid targets and also the possibility to form a toroidal ring having a sjherical shape* In the latter case, the current is sustained by REB and the heating of the confined plasma is attained by three dimensional adiabatic compressions* If this syste m s stablei expecn ca e exceeo t tw , Lawsone dth criterius usiny mb n ga 1 apparatus of feirly small scale*

49 SUMMARIES OP THE SESSIONS LASER SYSTEMS H. J. Doucet Ecole Polytechnique, Palaiseau, France

A considerabl inertiaeffore e th th per n f ti to l confinement program have been devoted and is still devoted to laser systems in order to increase the laser energy and the laser power by a considerable amount.

Fo futurra e laser fusion reactor ther presentls ei ideao yn l laser presenting simultaneously short wavelength, good efficiency, short pulse, high repetition rate, ... Nevertheless, several systems are promizing for the breakeven by laser. Present strong efforts are pursuing on several laser systems : Available power on target is increasing rapidly and is expected

to gro roughln i w y parallel ways durin nexe yearw th gfe tglasr sfo s laser,

3 electron beams and CCL lasers, to reach 10 W1 around 1976, increasing later to 10 W around 1984. Other systems as HP, Iodine lasers, later ions beams an laserX d s will probabl alse yb o seriously considere inertiae th n i d l confinement progra nexe yearsw th tfe f mo .

glasr Fo s laser which provides presentl highee yth r power, important improvement are made in laser components : Reproducibility, Beam quality in- cludin linealimitation ga no e r th phas f no e shif spatiad tan l filter, contro- lable pulse width, high gain amplifier are in progress despite of the numbe- rous difficulties presented by material strength which require good optical isolation in much more complicated systems. Classical solutions like KDP cellSjFaraday rotator, etc... are quite adaptable to large systems and are widel systemyw ne use n i ds with large diameters .comparisoA n between rods and disks turn ofte favoun ni rod f ro cheaper sfo r leas t prica d tean equa l beam quality.

The C0_ laser systems are presently improving very significantly using electron beam excitation hundrew fe .A d joule systemJ k s n o st n si single pulse are already constructed. Effective extraction of stored energy in short pulse have been improve measuree th : d d saturation parameter is explained by finite relaxation rate of rorationnal levels. Self focussing in amplifie avoid.ede b n rca .

New important progres e expectesar C0n i d_ laser components which shoul dlase- CO giv ro e t system hopefun sa l futur lasen ei r fusion program.

Iodine lase stils ri l interestin shorr gfo t wavelengt e pulsth y eb h despitpooe th r f efficiencyeo . Extractio storef no d energ repetitiod yan n rate have been improved significantly.

HF lasers coul alse db o interesting outsiders wit gooha d efficienc wild probablyan e l b y more widely studied durin nexe yearsw th gtfe .

New laser systems and laser improvements are clearly needed. Some new ideas have to be checked as for instance the frequency conversion of a 53 high intensit microwavf o y e radiatio frone relativistia th f to n o n c electron beam which could bring a tunable very intense infrared laser with wide spectrum^very short pulse and good efficiency.

Abou numbee tth lasef o r r beam t seemsi s presently clear that from our knowledge of symmetry properties in the energy deposition and of stability in the first stage of the target compression, the number of laser beams is mainly determined by the total required energy. Laser systems presently under studies include from 2 to 20 beams. Four beams systems are widely used and present already interesting symmetry propertie energn si y deposition.

54 INTERACTION OF LASER RADIATION WITH PLASMA Sili. Sige. V P d nlan Lebedev Institute of Physics, USSR Academy of Sciences Max Planck Institute far Plasmaphysik, Garching, PRO

Measurements of line shapes in the X-ray region can provide important parameter lasef so r fusion plasmas* Thi demonstratea swa Tondelly db o (Uhiv* of Paduao) measured electron density, electron temperature

and streaming velocit wn y of a Beryllium plasma produced by a ruby laser* The technique is now being improved by constructing a new spectrograph wit gracinha g incidence facussing device which allow spectrogrape sth h to be removed from the target without loosing spatial resolution* The interaction of intense laser radiation with the dense plasma produced i nplasma a focu undes si r investigatio Lebedee th t na v Institute* This investigatio essentialls nha y three aims* l) Durin firss git t compression phas plasme eth a focus provide shomogeneoua densd san e

T /* T. £ i keV c0 m1 n x A /5 6 ^* plasma use e whic b stud o d t n nonlinea e hca y th r interactio intensf no e laser radiation with plasma* Suc experimenn ha t allow te os on simulat e eth processes occurin corone lasea th f n ago i r irradiated pellet under well defined conditions* 2) Theory predicts enhanced absorption of an electron bea reduced man d threshold certair sfo n instabilitie targee th f tsi is preheated by a laser beam* These predictions can be experimentally tested durin latee gth r plasm e phasth f eao focus where intense electron beams plasme arTh e) a3 know focu. exiso it nt sn ti constitute intensn sa e source of neutrons, charged particles and radiation* It thus can be used to study engineering problem laserf so electrod -an n beam- induced fusion* plasmA a focus devic ek0 Jwit 10 condense ha r Nd-lase a band kan r with 20 beams have been built to study these problems* The laser is designed to pulses p installatioe 0 2 *Th a n i J n0 40 - 0 pulss 20 n r 0 eo 2 a deliven i J K r2 is now complete and experiments will start in the near future* Dr* Rudakov reporte theoreticaa n do l stud solitonf yo s which mighe tb create corone lasea th f n ado i r irradiated pellet* Laser-induced Langmuir turbulence was investigated by computer using averaging equations which include the effects of high frequency pressure on the plasma density* The main nonlinear effec thin ti s approac collapse th s h i Langmui f eo r energy whic excites hi y db 55 laser* A sresula collapsf to e energetic electron producede sar * Some estimates of numbe energd ran fasf yo t electrons have been given examplr *Fo temperature eth e of the fast electrons scales as follows *

T , = temperature of fast electrons q » pumping laser flux into Langmuir waves n = electron density c soun= s d corone speeth n dai

JMr* V. Silin reviewed the results obtained at the Lebedev Institute of Physic e USSth Rf o sAcadem f Scienceo y e interactioth n o s f laseno r radiation with plasma* Experiment reflectioe th n o s f laseno r radiatio plasmy nb conditionn i a s of parametric instability development showed tha reflectioe th t n coefficient for flow density values of 10-10 ^/cm2 in the case of a Nd laser in the nanosecond regime is less than 10%. In the picosecond regime the reflection coefficien greater e founs b wa o dt . Investigatio e directioth e f no th f no reflected radiation revealed mirror-type reflection. This showed that it s notioproductive i dielectria th f e no us o et c constan plasma f o t a with anomalously great high-frequency conductivity dependin e amplitudth n go f eo pumping. Such conductivity can theoretically change during the laser pulse, and thi s demonstratesi experimentalle th y db y observed oscillation timn si e of the reflection coefficient. Giving a unique interpretation of such a phenomenon particulan i d an , r separatin e influencgth f lineao e non d an r- linear effects* requiresexperimental e dependencstudth f yo f suco e h oscillation lasee th n rso pulse wavelength targee th , t material powee th , r flow densit radiatione th f yo , etc. Another sign of the anomalous nature of laser radiation action on plasma is the observed anisotropy of X-rays, corresponding to the appearance of electrons with a comparatively high velocity in the direction of light polarization.

Measurement Lebedee th t a s v Institut f second-harmonieo c energa s ya function of the flow density of laser radiation show that formation of the second harmoni s associateci d wit procese hth transverse f fusioo sth f o n e light wave with the longitudinal plasma wave arising as a result of transformation

56 of the laser radiation* The experimental relationship obtained differs from the experimental result Siegef so l et al.

The concep formatiof to secone th f dno harmoni resula s ca fusiof to n wavee ofth s arisin connection gi n with parameter effects mad possiblt ei e to determin secon e shifd eth re f fro tdo e harmonimth temperature cth d ean spatial distributio plasme th f nao nea criticae rth l point wher seconde eth - harmonic wave originates.

Finally, notions of the ponderomotive action of an electromagnetic field on plasma mad possiblt ei estimato et numbee eth fasf ro t ions accelerated by the field to an energy reaching tens of keV* In a picosecond laser regime picoseconcasa e f th eo n i r d(o structur nanosecona f eo d pulse )larga e part of the energy of the absorbed laser radiation can be transferred to fast ions* The difference in results obtained from the Lebedev Institute and from others may be due to the structure of the laser beam (in space and time), the contrast and other characteristics. The Garching group has investigated the case of plane, semi-infinitive target grean si t detail studo , t physic e yth interactiof so o wels t n a s la develo diagnostiw pne c methods* Results were presente shockwave th n do e propagatio targete th n blastwavn i ,o e formatio backgrouna n ni d gasn ,o densit temperaturd yan e distributio hose th t n plasmreflecteni n o d aan d

radiation froplasme mth a with frequencie experimentae s Th CO &2 .

58 LASER HEATING FOR MAGNETIC CONFINEMENT

Spaldin. J . I g

UKAEA CulhJun Laboratory

SEKIGUCH. T ) (1 I (Dept Electricaf .o l Engineering, Universit Tokyof yo , Japan). Professor Sekiguchi describe collaborativda e programme between 1? author thren si e department Universite th f so e Tokyth f y o d oan Institute of Plasma Physics, Nagoya University. The purpose of the programme is fourfold: develoo T ) fully-ionizedpa (i , impurity-free, laser-plasma source, having ion energies in the kev range, for a variety of magnetic confinement devices, (ii) To study the interaction between this expanding plasma and a magnetic field. (iii) To study the magnetic confinement of such plasmas, (Particular attention has so far been paid to spindle-cusp confinement; see Phys. Fluids jl?, pp 1895, 19?4) studo T (ivpossibilite )yth developinf yo intensn ga compacd ean t 1*lMev neutron source (10 101- 3 1B neutrons cm"2 s" eventuall1d ),an Dya T reactor, by extensions of these techniques. Pellet source (Mark I) Free-falling cylindrical deuterium ice pellets, having diameters of 100-40 0lengthd uran n 200-60f so 0 p m10x 10(i.ex J>16 - 6 1.8 atoms), are intercepte (stationarya y db ) focussed laser beam after falling vacuumn i m thit c A freel.0 s 1 somr distanc- yfo e7 trajectore eth f yo a 100 pm diameter pellet is sufficiently reproducible (i.e. within a few milliradians) to permit reliable interception using a 10J, 20ns, ruby laser - giving a fully ionized plasma of maximum ion energy 200ev. Electron-ion recombination is observed experimentally if the plasma is allowed to freely expand to > 15cm, due to the decrease in electron temperature.

Recent developments To permit reliable interception of the pellet at greater distances (30 - 100cm) from its source, an on-line computer-controlled system has been constructed to steer a Nd glass low beam (having an energy of 100-150J, in 20-60ns) on to the target. The present positional accuracy 59 systee ofth 60-9s mi 0 computationa e praTh . mechanicad lan l response of 30ms (each) have proved sufficiently short to permit the reliable interceptio xenof n o pellet e nic s dTOpja diameter, JOOjjm long) higA . h

repetition rate spherical H3 pellet injector, multi-beam irradiatioo n(t ensure greater isotrop plasme th f ayo glass/Cblob)d N d ,an O hybrid laser-irradiation schemes are now being considered. Computer simulation of plasma production A 1D, two-temperature Lagrangian code is used to compute the D burning and heating phase, assuming both classical and anomalous absorption; refraction and induced scattering are not yet included. A wide range of calculations, including the effects of power variation and prepulse, were wavelengths d reporteN d an botr drealistifo O r h C Fo . c pulse durations energe ,th y absorption efficienc predictes ywa typicalle b o dt y 50$ - O laserC 5 ;2 s appeare attractive b o dt sucr efo h applications. Other work Strong plasma assymmetries were experimentally observed when thin glass wire targets (10 10, ,020 ^0 omr 50 dia) were irradiated transverse tconfininoa g magnetic field. Feasibility studie intensn a r sfo e 1*fMev neutron source were also outlined and discussed in detail in Session IX.

(2) I. J. SPALDING (Euratom/UKAEA Fusion Association, Culham Laboratory.) Spaldin. Dr g apologize provet no dd d ha thapossibl t ti organizo et e meetine talkth t scoveo a g t significan e rth t work being undertaken ni the U.S.A. U.S.S.R.d ,an thin ,i s field. Within Europe, verthera s yewa active interest in laser-filling present-generation toroidal confinement devices reasonr ,fo s previously outline Euratoa n di m Advisory Group Report on Heating and Injection (EUR. FU.7VAGHI 10/R1; Section B.5(c).) thaf o Pag t5 e7 repor t tabulates important parameter sevef so n contemporary European machines, most of which can contain plasma energies of order 1kJ; future requirements wil muce lb h greater somr Fo f .eo these application compet o laset e sth s rha e with very efficient alternative heat sources (eg. ohmic heating neutrar ,o l injection). However, laser technology is still progressing very rapidly; already electrical efficiencie somf so e 60J5200d >an $ have been claime(lonO C r gd fo pulse , electrical discharge) and HF (short pulse, chemical) lasers, respectively. For some confinement experiments, it could prove very useful to avoid externally induced plasma currents. Both Garchin Culhad gan m were therefore involved in such work (for WIIB and CLEO stellerators respectively co-operativpara s ) a f to e Euratom programme hopes wa dt I . 60 to use a Garching-designed H pellet source on both, experiments, but it 8 appropriatt describo t no othee m s worth e hi wa reth f r k o laboratorie efo s in greater detail. The Culham experiment would use a 160 litre-atmosphere electron-beam preionized CO laser to provide the main heating pulse, although A = 1 8 or 10|jm prepulses could also be used if required. The commercial (Systems, Scienc Sofd ean t ware) cold-cathode electro beed ha n n successfullngu y operate energiet da 270kvo t usep d s u ,preioniz o an d t active eth e laser volume of 200 x 20 x 20 cm. The amplifier is at present operated at atmospheric pressure, wit reproduciblha e energy depositio somf no e 200J/litr 120ka t ea v sustainer voltage. Optical measurementsd ,an sustainer commissionin atmosphere2 t ga s (usin 200kvga , 62kJ sustainer bank currentls )i hand n amplificatioye i Th . pulsef no s havin duratioga n between 1 and ~ 100 ns in such an amplifier has been analysed numerically (Armandill Spaldind an . oE g I.J .Culha- m preprint CLM-Pte3, 1975). Optimizatio energe th f yno coupling betwee targee laseth e nd th t ran requires a detailed understanding of non-linear laser-plasma interactions. Preliminar O laser-plasmyC a interaction measurements have therefore been mad (vacuumt ea ) intensitie ~10o t 13p w/cmu f so 3 (Donaldso alt ne , Proceedings of 7th European Conference on Controlled Fusion and Plasma Physics, Lausanne, Switzerland, September, 1975); this work included the first direct measuremen laser-inducea f to d density-cavitr y(o soliton). Such effects could have an important influence on the coupling, as predicted numerically by Estabrook, Valeo and Kruer, among others, and were also relate spectrae th o dt l shift scatteren si d light discussey db Professor Yananaka this morning summaryn I . , several alternative scenarios for the future could be envisaged, depending on (related) scientific and technological laser developments within the next few years.

61 IMPLOSION DIAGNOSTICS USING X-RAYS J.P. Babuel-Peyrissac and G.W. Kuswa

Centre d1 Etudes de Limeil, France, and ERM, Washington DC.

A. X-ray diagnostics at Limeil (j,P, Babuel-Peyrissac) Implosion experiments at Limeil for 1975 and 1976 will be made with a four-beam neodymium laser, in tetrahedron configuration at , gaussia ns levea KJ 1 3 ,f o l n pulse* Three kinds of X-rays diagnostics are planned* 1) Pinhole cameras 2) X-ray microscope 3) Radiography method (Absorbix) Calculations which were made wit assumptioe hth a s i nJ tha0 50 t absorbed by a spherical polyethylen target when it is irradiated by the four-beam laser with an energy of 1 KJ, give at an initial diameter of 75 /u and an initial mass of 1.63 /ug the following t parametercoreho e : th t a s compression ratio ^o 15 f 20 temperature T 200 £ 300 eV s p 0 6 life time Usin gfive-beaa neodymiue th f mo m laser, synchronized wite hth main fou aluminiun a r beamst hi mo t , target produce w , X-ran ea y spectrum* After collimation through the target, and using a mono- chromator to separate the K-alpha line, the X-ray beam is analyzed X-rabn ya y streak camera conversioe *Th n ratstudies ewa t dLimeia l and results show that it is necessary to have around fifty Joules on the aluminium target to obtain ten milli;joules of the K-alpha line across the target* The X-ray streak camer Thomsoa s i a(TSe on nN 503 phot)w witne o ha cathode studied at LEP and Limeil* Presently we use 100 a of gold on a beryllium foil (10 /u)* Taking into accoun e photocathode yielth th t f do "t5 e ( eo th 1% d )an contras K-alphf o t a line, calculation show s s possibli tha t i t o et observe the variation of the compression with the time and estimate its value to an order of magnitude*

B. Diagnostic E-Bean i s m Experiments (G*W, Kuswa) Pinhole pictures are a major tool used in the inertial confinement program to diagnose pellet compression* A refinement which has been parti- cularly valuabl e e-beath n mei progratargea e f materiabees us o tm ha o n t l identical to the pellet as a point x-ray source for obtaining the point,» response functio ne camera oth fmateria e t wit*Th hi poinha s i l t electron beam source lineasuca s ha r electron accelerator operatin same th et ga

63 voltage used for pellet implosions, and a reference picture is produced* This reference is used in a numerical routine to enhance images of target shots taken with the identical pinhole camera apparatus* In this way vastly improved image information is obtainable* The same technique should be of use in laser implosion work. MicroChannel plates have also been useful in x-ray diagnostics to boost the sensitivity of x-ray pin hole cameras and to use in the gated mode for resolving events on the nanosecond time scale* A very high contract ratio camera has been made using two lonm channec g0 3 solenoida a l f plateso eacn d i hen e l ,on magneti c field for focusin electroe gth n image firse .Th t channelplate convert incidene sth t x-ray imagcorrespondina o et g electron image secone *Th d channelplates amplifie electroe sth n immag preprintind ean g focuse ontt si phosphooa r screen coupled to film* The film end of the camera is shielded from the x-ray event to be diagnosed, the camera is gated by applying pulses to both channelplates, usuae Th l applicatio camer e obtaio th t f s nao i n x-ray shadow imagef so imploding e-beam pellets at various times after the e-beam is fired* The x-ray source used is a small flash x-ray source of 5 - 1 Mev and ~5 K& x-ra e camere th *Th m y m d sourcaw an wit fe qLmultanousl e area n eh a ar f ao y triggere desiree th t da d interval afte e-beae rth m implosio initiateds ni *

64 THE ROLE OF SMALLER EXPERIMENTS IN THE USER FUSION PROGRAMME

M* Gryzinski Institute of Nuclear Research, Warsaw

A round table discussion on the role of smaller experiments in the laser and electron fusion programme was held during the meeting* It has been pointed out that a search for finding the most effective way of reaching "the final goal should be one of the aims of the meeting* The improvemen f exchango t f scientisteo informationd san , especially betwee e larg nsmalleth d ean r centers mose th , te seem b importan o t s t problem at the moment* The Agency, with the help of a number of scientists from different countries, should take care of it* opinion Thera s ewa n expressed thae participatioth t f smalleno r centers whose main line of interest is not exactly laser and electron beam fusion, should be profitable for both the big fusion program and for these centers* There were listed problems whic e importanhar r fo t e lase electroth d an r n beam fusio could nan solvee d b n differendi t center l oveworldsal e th r *

List of problems important to laser and electron-beam fusion: 1. Basic physics 2* Diagnostics 3* Technology Real equatio f statno e Photoelectric effect Energy storage Nuclear cross sections ' e rangeJ Energy transfer ———— •

Stabilxty ana^si s Photocathods n i mmma9

High pressure discharges ^ ionized gases Discharge physics Transport properties '•Brand X" laser Intense X-ray sources

65 CONTRIBUTED PAPERS LASER INTERACTION WITH PLASNA

J. Mizui Kang. ,H Sasaki. ,T , K. Yoshida, T. Tschudi, N. Yamaguohi, T. Yamanaka, Yamanak. C a Institute of Laser Engineering, Osaka University and Institute of Plasma Physics, Nagoya University

Synopsis

In orde investigato rt coupline eth g of laser lighd tan plasma, we have performed the laser bombarding experiments on the hydrogen and deuterium solid targets using a glass laser system "GEKKO-X", with energy of 50 J in nsec pulse. decrease reflectivitTh e th f eo appeares laseye ha th rt da intensity of one order of magnitude larger than the threshold parametrie ofth c instability phasA . e modulatioe th f no reflected light has been found to be due to temporal changes of the refractive index. A second harmonic generation and its red satellites with an isotopic effect have also been observed in the hydrogen and deuterium plasma. These experimental results of the laser interaction with plasma can be explained by a linear conversion of the laser light field intplasme oth a wave nea cutofe rth f relate s regioit d dnan nonlinear processes in higher laser intensity.

Preliminary compression experiment has been tested using glasa s laser system "GEKKO-II" nsen witi cJ h 0 energ25 f yo pulse/ by the holographic technique. 69 . INTRODUCTIO1 N Recently much attention has focused on the laser fusion scheme using high density plasma produced by the implosion. perforo T scientifie mth c feasibility experimen lasen to r fusion shoule ,w d resolv followine eth g three subjects: physics of laser interaction with plasma, techniques of high compression of plasma and the development of high power, highly efficient lasers. interactioe Th n betweee th nf o lase plasme d ron an s ai most interesting phenomen lasen ai r plasma research. 1—3 In particular nonlineae ,th r couplin collective th f go e process in plasma is very important for heating? The parametric process (photon-plasma-photon interaction)5-7 play essentian sa anomaloule rolth n ei s absorption. This process gives the high energy particles; the decrease of reflectivit lasef satellited yo re re lighth d stan witn ha isotopic effecsecone th n dti harmonic generation. Q In the recent scattered light measurements, we have observed a self-phase modulation of the incident laser light. This is caused by a different mechanism to that of the red satellite in the second harmonic. To explain these experimental results presume ,w lineaea r mode conversiof o ' n 9 10 the laser light into the plasma wave in the oblique incidence. The second harmonic 11 '12 is produced at the resonance (cutoff) region, whil fundamentae eth l lighs ti reflected froturnine mth g (near cut-off) regione th n I . nonlinear proces turnine th t sa g region spectrue ,th m broadening both the red and blue in the reflected light shows the self-phase modulatiotemporae th o t le plasmchangne du th f aeo density ponderomotivcausee th y db eparametrie forceth t Bu . c 70 process (containing a decay and modulational instability)13 make large sth e amplitud resonance th wavn t a eio e e region, whe lighe nth t intensit beyons yi threshole dth instabf do - wavilitiesn io e e maTh y. induc Brillouie eth n scattering carrying the red shifted satellite in SH6712 preliminare th r Asfo y implosion study glas,a s laser system "GEKKO-II" nsen ,i energcJ puls0 useds y25 e ewa Th . two beams were irradiated upon various thin targets. The time resolved hologram was taken:.to check the formation of shoofe wave plasman si . The interference patter cons nwa - structed afte lasee rth r bombardment generatioe Th . n source of the x-ray was searched by a pinhole camera. The large glass laser system constructio"GEKKO-IVn o w no e "ar r nfo the scientific feasibility experimen lasef to r fusion.

2. EXPERIMENTAL ARRANGEMENT The laser system "GEKKO-I" was composed of the oscillator and 5 stage amplifier section. The oscillator section had YAG and glass socillators which were selectively used to change the laser light spectral width. They were 6 and o 60 A respectively. The oscillator delivered either the Pockels cell Q-switched pulse or the mode locked pulse train/ both of which were tailored by the pulase transmission mode technique. The output energy was «50 J in nsec pulse and the beam divergence was less than 1 mrad. maie Th nexperimentae parth f to l setu shows pi n ni Fig.l targete Th . s were solid deuteriu hydroged man n sticks, lasee Th r . beamm th f m0 o e 1 dimensiox 2 x whic2 f no s hwa 40 mm in diameter was focused onto the target by an aspherical lens of local length 50 mm. The focal spot diameter was 71 about 50 ynu The image of the target was magnified 10 - 20 times to check the focal condition. The accuracy of the focal adjustmen. ym 5 2 s twa The reflected and scattered light spectra were investi- inciden e range th gateth f en o di t spectru secons it d dman harmonic using a Czerny-Turner grating spectrometer with a mean dispersion of 8 A/mm in first order. The spectrum of the infra-red regio observes nwa d usin infra-ren ga d vidicon (PbS Photo-surface) inciden e ratie th e Th .th f oo o t reflected laser light was measure usiny db singlga e biplanar photodiode, HTV-R317, wit filterha , IR-80. The electron temepratur estimates ewa d frosofe mth t x-ray measured by plastic syntillators with beryllium windows of different thickness (100, 200, 400, 800 ym). glasA s laser syste "GEKKO-IIf mo " uses (Tablwa d ) eI to testif implosioe yth n proces usiny sb beamsg2 e Th . thicknesn targe i thia m s y n t wa 0 plasti s10 w cfe a fil f mo diameten i m y 0 pelletrd 5 an levitateo t 0 ,2 vacuun i d y mb CW Ar laser light. Fig.2 show experimentae sth l arrangement time th e f resolveo d hologra shoce th kr procesmfo plasman si . It can take a series of framing pictures whose time spacing psec0 idouble s10 Th . e explosur accomplishes i e e th r dfo inteferometric hologram.

3. EXPERIMENTAL RESULTS Lase1 3. r Couplin Plasmo gt a 3.1.1 Reflection of laser beam and plasma heating The electron temeprature estimated by the foil absorption method of soft x-ray from the plasma .is shown in Fig.3. In the glass laser system, the reflectivity increased up to 72 begad an decreas 1o n8% t e abov lasee eth r intensity of 1.5 x 10 W/cm2, which is one order of magnitude larger than the threshol parametrie th f do c instability electroe Th . n temperatur componento tw d eha s above this threshold highe Th .- energy componen spatiae t th increasewher , s i l eP P s da 1 2 averaged laser intensity low-energe Th * y componena d tha dependence of P . The ion velocity had also two components. These results were reported before?A lase6 YA re casth systeme Inth f e o reflectivite ,th y always wa s slightly higher tha glasne thath sf t o lase r systemseparatioe th high-ane d ,th an f no d low-energy com- clearlponentt no s yswa observed. The neutron measurement has been performed by glass and YAG laser system. Fig.4 shows the relation of neutron yield versus laser energy neutroe Th . n productio assumes nwa o dt be isotropi whole th er solicfo d alss anglewa ot I . checked experimentally usin locatinga g technique thae tth main targeneutroe source th th s f teo n t wa itself ge o T . the same yieldamoune th YA e f ,tGth o laser system needed twice glasenerge th sf y o one dependence .Th e th f eo neutron yiel laseo dt r energy accorded witpowerh h5t f so the energy in the low power and as pointed by the Limeil group 17 '18 tende saturato dt hige th h n powerei .

3.1.2 Scattering spectra of laser beam We performed measurements of the angular distribution spectrane scatteree dth th f ao d light aroun wavelengte dth h incidene Ofth t laser, 1.0secons 6it vimd dan , harmonics, « 5300 A. Table II summarizes the results for the scattered light at the direction of 0° (backward), 45°, and 90° from 73 the laser beam. The second harmonic and its satellites on the red side were observed8'19'20 in all directions when the electric-field vectoincidene th f ro t laser lighs twa perpendicular to the plane including the wave vector k of the incident lase rscatteree lighth d tan d lightt Bu . they were only observe backware th n di d direction whee nth electric field directio than i ts planenwa .

powee Th r dependenc back-scatteree th f eo d second harmonic was found to be proportional to the square of incident laser power wit thresholo hn lasen do r power. This is due to the linear mode conversion..

Abov threshole eth d laser parametri e poweth f ro c instability it was accompanied by -two side peaks in the red sid shows ea Fig.5n ni . These side peaks were especially clear when the YAG laser system was used. They appeared at first in the central part of the laser focus, where the laser intensity reache threshole dth parametrie th f do c process. As the laser intensity increased, the intensity of the backscattered light were pronounced and the spatial backscatteregioe th f no r source became th er widefo s A . rat increasf e o sid e th e f epeako s with laser intensity, the glass laser system gav elargea r rate thaYAe Gnth system did frequence Th . y firsshifte th tf s o pea k with thsysteG eYA m havin intensite gth 0 1 W/c x my8 wer4 e8 13 2 and 79 cm from the center of the second harmonic for hydroge deuteriud nan m plasmas, respectively shifte Th . s of the second peaks were 319 and 204 cm*" , respectively. These second peaks showed' an isotopic effect. These shifts had no power dependence* In the case of the glass laser 74 system incidene ,th t spectru broao s s d mwa tha fine tth e structure of the scattered light was smeared. The spectrum around the second harmonic is not due to scattering excited in the underdense region. These side peaks of the second harmonic seems to be created at the resonance closel e regioar d ynan relateparametrie th o dt c instability. The spectru scatteree th f mo d light aroun incidene dth t wavelengt affectes focahe wa th ly db positio lasee th rf no beam backscatteree Th . d spectrupeako tw sd mabovha e eth laser 3 0 intensit W/cm1 x 5 2 whef focae yo nth l poins twa in the ranges of 50 * 150 ym and 100 *v 200 pm beneath the surfachydrogee th f deuteriued o nan m targets, respectively. incidene d sidth re f eo e tth wavelengt t a s wa d e han On anothre was at the blue side as shown in Fig.6(a). However, the backscattered spectrum showed only one peak at the red e side of the incident wavelength by 3 ^ 8 A when the focal point was out of the above-mentioned region or the laser intensit belos blue-shiftee 1x ywa 0 th w5 d W/cAn m. d 13 2 peak was not observed at the direction of 45° and 90° from the laser bea mlasee eveth rt na intensit 0 1 W/c f yo m 14 2 as show Fig.6(a)n ni frequence Th . y blue e shifth -f to shifted peak frocenteincidene e th mth f ro t spectrus mwa o deuteriue th r fo 1 m7A laseplasme th rt a intensit f yo 1 x 1014 W/cm2. It increased slightly with the laser intensityisotopio n d ha cd ,effectan onsee Th .t timf eo the blue peak was near the time of the maximum of its intensit incidene th f yo t pulse whose duratio nsec3 s .nwa The maximum of its intensity appeared after 1.5 nsec from that of the incident pulse. On the other hand, the onset of 75 peathd ere k was delaye nsed1 c from tha tincidene ofth t pulse, and the time of the maximum intensity coincided with tha thf to e incident puls shows ea Fig.6(b)n ni ?

2 Preliminar3. y Result Targef so t Compression Fig.7 indicates the various holograms under different focusing conditions Figs.7(an I . 7(b d lasee )an ) th r focus is just on the surface and within the target at the depth of about 200 pm, respectively. We can say that the focal condition is very important to implode the target. From the figure shift of the hologram interferometry the compression ratio was estimated about 3 in solid targets. The x-ray pinhole camera was used to measure the spatial distributio energetif no c electron keVenerg0 e 5 Th .s . ywa

DISCUSSIO. 4 N 1 Linea4. r Mode Conversion A second harmoni generates ci d only whe matchine nth g

condition, 2k&(a) ) = kt(2o)o) or k&(w ) + kt(o) = kt(2a>Q), are satisfied, wher wavs i ek number ,stant suffid dan x£ for longitudinal and transverse waves respectively, and w e frequencth e ar f electromagnetid (iy)o an d electrocan n plasma waves respectively. Fro experimentr mou secone sth d harmonic has no threshold or very low one. The laser light is converte electron a o dt n plasma wave unde conditioe rth n of an oblique incidence. The resonance region is a source secone ofth d harmonic othee th rn O .hanincidene dth t laser ligh reflectes ti d froturnine mth g region, whics hi apart froresonance mth e region. Fig.8 show situatioe sth n of these regions. We assume that the electric-field vector is in the x-z plane. 76 Fo scalra e lengt plasmf o hL a inhomogeneit waved yan -

lengt electromagnetie hth \f 0o c wave/ optimuthern a s ei m

angle of incidence 6O for maximum conversion to a electron plasma wave;9 (2irL/A )2/ '3 si2n 6 ^ 0.7. Substituting L = 80 ym and X = 1.06 ym, 8 is equal to 5°, while the maximum

incident angle 6m is 21.8° in our experiment. As 2TfHQ/\o = 3.9, where & is the distance between the resonance region (refractive index N=0) and the turning region

(N = sine ), the distance Am between the maximum fields of the turnin resonancd gan e th n eO regio . ym abous ni 1 t1. 2 L 1/3 other hand the width of resonance region/ A = (*D" ) **

0.16 ym/ where XD is the Debye length. Because &m » A, reflectioe consideth y d ma an e w incidenf 6 nro SH tha e tth t laser ligh independene tar t phenomena/ whic showe har y nb our experiments.

4.2 Second Harmonic Generation (Resonance Region) mechanise Th geneatioe th secone f mo th f dno harmonic is an interaction between the electromangetic and electron plasma waves in the resonance region. The theoretical predictions 12 hav followine eth g characteristic features: (1) The intensity of SHG increases guadratically with the intensity of the incident electromagnetic wave. (2) The electric field vecto SHf parallers o Gi xe directionth o lt , It propagates almost along z direction, and can not propagate paralle directionx o lt ) Abov (3 e .threshol eth d parametrie poweth f o r c instability wavn io e n ,producea s the red satellite around SHG. But the blue one is strongly damped. These aspects are closely agreed with our experimental results. 77 Fro theoreticae mth l result, temporall•7 y growing modes of paf ametric decay instability into ion-acoustic arid elec- v » ' * tron plasma waves vicinit e exis resonance th th n t i f yo e region across the density gradient, due to the resonance pume ofth p wave orden I .riso rt e this instabilitye ,th rate of trapping the wave energy in the resonance region (cavity) must be faster than that of leaking the energy due to convection. This requirement can be expressed by the inequality}4 electron-plasme fiele th th f dwhero s i eE a wave, whics hi J? linearly converted from, the electromagnetic wave. If

ty O |£. e electromagnetipJe fiel th th S5 f *?wherdo s , i JI E o eE c o wave, the threshold power for the cavity formation is 2.7 x 103. 3conside e W/cW m. 1 r that this valu equivalens ei t threshole toth parametrif do c decay instabilit shows ya n in Fig. 3. Now we can explain the spectrum around the second harmonic as follows: Under the threshold the second harmoni s generateci d wit e conditiohth f 2oino •*r o 2w

*w + w -»• 2uQt where

78 and

where B.S. is Brillouin scattering process. The frequency of ion-acousti cparametrie wavth n ei c decay instabilits yi 12 12 deuteriur fo IOx z 3 /2d H hydroged " x an io x man 3 H n z plasma respectively. In Fig. 5 the shifts of the second side peak deuteriuf so hydroged man n plasm experimentalle aar y 12 1 12 1 6.11 x io Hz (204 cm"" ) and 9.56 x IO H z (319 cm"" ), respectively value verTh e . ear y abov e closth eo e t estimate d shift 2JT. S 3 Plasm4. a Heating Under the threshold of the parametric process the laser energ mainls yi y supplie electroo dt inversy nb e bremsstrahlung; The dependence of the electron temperature on the laser power can be estimated by considering the hydro- dynamir bees Ou c ha n' . P motioT d e foun^ « b an o ndt 6 expeirmental results show in Fig. 3 that this law holds for energthw elo y componen electronsf to . Abov thresholde eth , taking account of the anomalous absorption, the relation

2 2 T derive'«P s i 3 4/ d hydrodynamifroe mth c analysis. These Q results agree with Pig. 3. decrease Th reflectivityn ei , which beginlasee th rt sa intensity larger tha threshole nth parametrie th f do c process, by nearly one order of magnitude, is explained as follows: At the threshold, the spatial region of the instability is restricted in so small area of the focal point that the reflectivity is still mainly determined by the broader area where the laser intensity is weak enough to introduce the classical absorption lasee th rs A .intensit y increasese ,th 79 anomalous absorption grows spatially to a larger plasma volum reduco nt reflectivitye eth .

The difference of heating effect between the YAG and glase th s syste spectracausee s mi th y db l e widtth f ho incident beam. Nishikawa and co-workers2 3 have presented a theoretical treatment of the double resonance of the parametric excitation using two pumps, both being in resonance wit electroe hth n plasma oscillatio same th e t a d nan time their beat frequency being in resonance with the ion- acoustic frequency. According to this theory/ two features result Whe) beae (1 n:th t frequency tune s i A wtwico dt e

the ion-acoustic frequency 2&s and Ygis the damping rate of the electron plasma wave, the total threshold power for wavexcitation io e e becometh f no s much lower than thaf to singla whe e) firse pump(2 nth d t ,an pum p intensits yi margina decae th yr instabilitylfo ,vera y small second pump

red shifted by ftg can produce the oscillating two stream instability* The glass laser had a spectral width of 12 AwQ * 1.6 x 10 Hz (corresponding to AXQ » 60 A), whereas 11 the width of the YAG laser was only 1.2 x 10 Hz (AXQ» • 12 A)6 . Consequently Hz casr i* Ynf ou e o e0 1 > &x Bt3 ,Hs i g expeconn e ca glas e tth s lase approximato rt conditione eth s fo doublra e resonance much close laserG r YA tha e .n th This line of reasoning also applies to the excitation of the oscillatin streao gtw m instability which require large sth e pump threshold than the decay instability. Both types of instabilitie inducee b n sca d more readily wit broadbane hth d glass laser. This effective anomalous absorptio shows ni n by the neutron yield in Fig.4. 80 The mechanism of neutron emission by laser have been discussed in the hydrodynamic approach. When the shock heatin dominans g i overdens e th n ti e region numbee ,th f ro neutro proportionas ni Wo l5t , wher lasee th e r s Wi energy . And if the electron heat wave is dominant/ the one is excese casth e f proportionath seo n laseI . r powerW o lt , the most absorbed energy transform electroe th o st n energy, electroe anth d n heat front preheat overdense sth e region and breaks the shock formation. This effect is also observed in Fig. 4. 4.4 Self -Phase Modulation (Turning Region) The electromagnetic wave is mainly reflected from the turning region, and the spectrum broadening around the incident wave length could be attributed to the self-phase modulation of the laser light due to temporal changes of the refractive index ,functioe whicdensitye th th s hi f ne o W . presented a time-dependent behavior of the scattered light in one-dimentional simple model* Without absorptiod nan charge saparation, the E.M. wave equation is given by

o wher egroue vth p«k/s c i velocitw y func e whicth -s hi densite th s i y perturbatio n d e an th t f d no an , z tio f no f 2) second-order equatione Th .plasme th uniforn f asi o m temperature are given by

81 densite th s zeroth-orderf i yo wher en ,e vth * s 'i f\ T m velocity perturbation of the second-order and Cg «= e/ - is the ion sound velocity. When the slowly varying amplitude of the E.M. waves is

represented by EQ = AQ e^Ud^ the real part of eq. (1) gives

The phase difference between the reflected and incident wave is

The frequency shift is

Therefore the density change near the turning region (v/c * 0) mostly contributes to the frequency shift. Near the turning region, a large negative gradient of the laser intensity, especially in |E |*y , appears to introduce a the decreas plasmf eo a densit eqs.(2y yb d (3)e )an Th . spectrum broadening due to the phase modulation at the turning regio lasee sidth d n rre f e appearo lighte th n si . For the higher laser intensity, a swelling hump of the laser intensity due to the amplitude modulation becomes so large that a cavity of the plasma density accompanied with hump fronn si rea d producets an r i underdense th n di e region. Then the back-reflected light shows the blue shifted row as 82 shifted re e weldth peas la k intensit e ofth shows ya n ni Fig. 6 (a). When the pulse width of laser is long/ a steady state condition gives proportiona s i Atd oan ) (3 fro . meg o ..l .t >|PolVS^T " From this reaso temporae nth l Figresponsn i blu e w .th e ro f eo 6(b) is delayed from the red peak, owing to the slower formation of the density humps in the underdense region. 2 22 Judging from the dispersion relation oro = c*sk in eg. (2) and egwaven .io (3)se ,responsiblseemth e b o st foro et m the density humps.- threshole Th blude poweth e r shiftes rfo i w dro estimated as follow. The rate at which E. M. wave is amplified near the turning region must be faster than the rate at which the ion waves propagate over the region. From the eg. (1) this reguirement can be expressed by the ineguality

threshole andth 1x 0 d 4 powe4. w/c s ri . mThi s value 13 2 agrees the experimental threshold. This effect is small for the second harmonic, because v (2u )/C £ 1 in the turning region (cf. eg.(6)). 83 amounfrequence e Th th f to y shifs ti 1

where d lasean r 1x 00 powe 1 1 x s W/c *rc i v5 / , m 1A O *• ^ At • 10 sec. The difference between the two peaks in Fig.6(a) agrees with 2Aw. in the case of the laser- produced plasma mediue ,th m expands towar lasee dth r beam. The 'whole nth e spectru broadenine th f mo shiftes gi d about o blue th e o Doppleresule sida t th s A e a f 6 to r effece tdu to the expanding velocity, 1.8 x 10 cm/sec. ;rhe over- lapping of the frequency broadening due to self-phase modulatio Doppled nan r shif explain tca experimentae nth l results.

5. CONCLUSION scatteree Th d light aroun wavelengte dth e th f ho incident laser and its second harmonics was observed experimentally. Because the second harmonic has no threshold lasee ,th r ligh linearls ti y convertea o dt electron plasma wavresonanca n ei e region unde condie rth - obliqun tioa f no e incidence resonance Th . e regioa s ni source of the second harmonic. While the incident laser light is reflected from the turning region. The spectrum broadenin blud an ereflecte e d gsidth re bot f ee o hth d light show self-phase sth e modulatio turnine th t na g region. The ion wave caused by the parametric process in the resonance region induce Brillouie sth n scattering carryine gth red shifted satellit SHGn ei . 84 The energy of high power laser was anomalously absorbed by the electrons in the resonance region. In the case of the excess laser powe electroe rth n heat front breake sth shock formation experimentr ou n I . efficience sth r yfo neutroe n th yiel f 10bettex s o d144 wa ) W/cmJ t ra 5 (1 2 broad band glass laser optimue Th . m condition dependn so the hydrodynamio behavior, whic decides targee hi th y tdb dimensioeffective th d an ne transport coefficientt I . wil nexe lb t proble searco mt h this transport coefficient above th dueo et mentione d instability.

Acknowldegement The authors wish to thank Professor K. Nishikawa and Mim. stimulatinr K afo . Dr g discussioFukushim. H . Mr r d afo nan his assistanc performinn ei experimentse gth .

References

) 1 N.G. Basov, P.6. Kruiukov, S.D. Zakharov, Yu.V. Senatsky and S.V. Tchekalin: IEE Quant. EJ . Electron. 4_ (1968) 864. 2). F. Floux, D. Congard, L.D. Denoeud, 6. Piar, D. Parist, J.L, Bobin, F. Kelobeau and C. Fauquignon: Phys. Rev. A 1 (1970)"821. ) 3 Laser Interaction with Matter, editeYamanak. C y db a and H.J. Schwarz (Japan Societ Promotior yfo f no Science, 1973). Yamanaka. C ) 4 Yamanaka. ,T Sasaki. ,T Yoshida. ,K Waki. ,M , and H.B. Kang: Phys. Rev. A £ (1972) 2335. 85 Nishikawa. K ) 5 Phys. J : . Soc. Jap. 2A_ (1968) 916, 1152. €) A.A. Galeev and R.Z. Sagdeevs Nucl. Fusion, 13 (1973) €03. 7) R.B. White, C.S. Liu and M.N. Rosenbluth: Phys. Rev. Lett., 31 (1973) 520. 8) C. Yamanaka, T. Yamanaka, T* Sasaki, J. Mizui and H.B. Kang: Phys. Rev. Lett (19742 .3 ) 1038. 9) V«L. Ginzburg, The Propagation of Electromagnetic Waves in Plasmas? (Pergamon Yorkw ,Ne , 1970). 10) O.W. Forslund, J.M. Kindel, K. Lee, E.L. Lindman and R.L. Morse: LASL Report No. LA-UR-74-894 (Univ. California, 1974). 11) N.S. Erokin, S.S. Moiseev and V.V. Mukhin: Nucl. Fusion, 1_4 (1974) 333. 12) K. Mima: private communication.

Ikezi. H Nishikaw) . ,K 13 Mima. K Phys . J d :a an . Soc. Jap., 3_7 (1974) 766. 14) G.J. Morales and Y.C. Lee: UCLA-PPG Report-211 (Univ. California, 1975). 15) M. Waki, T. Yamanaka, H.B. Kang, K. Yoshida and C. Yamanaka: Jap. J. Appl. Phys., 11^ (1972) 420. Yamanaka. C ) 16 Yamanak. ,T Sasaki. T d aan "Lasen ,i r Interaction and Related Phenomena", Vol.3, edited by H.J. Schwarz (Plenum Yorkw ,Ne , 1974) 629. 17) J.L. Bobin: ibid, 465. 18) F. Floux, et al. ibid, Vol.2 (1972). 19) J.L. Bobin, M. Decroisette, B. Meyer and Y. Vittel: Phys. Rev. Lett 0 (1973.3 ) 594. Eidman. K Sigel. R ) d n:20 an Phys. Rev. Lett. 3^4 (1975) 799. 86 ) J.L21 . Bobin: Phys. Fluids, 14_ (1971) 2341. 22) T. Yabe and K. Niu: J. Phys. Soc. Jap., 37 (1974)- 1445. Arnush23. D ) Nishikawa. ,K , B.D. Fried, C.K. Kenned lan A.Y. Wong: Phys. Fluids, 1£ (1973; 2270. 24) C. Yamanaka, T. Yamanaka et al.i Phys. Rev. A., 11 (1975) 2138.

TableI High power glass laser "GEKKO-II".

MAIN AMP BOOSTER LASER PREAMP I II III IV V Kp DISC I II III

ROD tnm) l DIMENSION 5*33fl 2 10 20 20 30 30 25 100 100 100 too •asp*' **-» m 212 212 142 142 178 98 (08 108 108 INPUT ENERG) J ( Y 0,002 0.0 4 0.56 4 7.2 12 50 120 OUTPUT ENERG) J ( Y 0.04 0.56 4 7.2 12 50 20 240 GAIN 7 40 7 1.8 1.6 4.2 2.4 2 (THREE PASSES)

87 Table II

Angular dependence of scattered light. Case A is for JE (for the incident laser sight) Perpendicula plane th f ffeeo o rt (for inciden scattered tan d light) r 2.Cfo Cass i eB e /feth n planei .

Frequency threshold (W/cm2) Measurement location Backscatter (0°) 45° 90°

A no yes yes yes w -Aw no yes yes yes

A (5*10) xio13 yes no no (00+Au> ^ « yes no no

A no yes yes yes 2W° B no yes no no

A (2*3) xio13 yes yes yes 2w -Au) B n yes no no . Soft X-Roy CM

Neutron Detector

Spectrometer

IRvidicon

Line Selector Video Recorder Controller

Fig.l Main par interactiof to n experimen glasd N y stb laser (GEKKO-I).

Double exposure i I I —»t Q.53 jj I L. 1.06 p

M. Amp. Optical Delay

Fig.2 Arrangement for time resolved holography for shock proces plasmn s i lase 6 YA a r f usino systemG gSH . Time resolutio psec0 10 *s ni 89 TeocP" o-'BeAOO>J/800p > * • x:Be100jj/200p 5 I 20 I2 to~ 5 5 CIO* u Io Parametric Threshold . 1 10" 2 5 10'* 2 5 Laser Intensity (W/cm*) Fig.3 Electron temperatur reflectivitd ean y versus laser intensity when glass laser system bombards a solid deuterium target. Threshold of parametric instability is indicated by vertical line.

10*

to'

10 0 2 » 15 2 50 Laser Energy (J) Fig. 4 Neutron yield versus laser energy. 90 YAG 5461g H A 319cm"1

5461 5400 5350 5320 5300 Wave Lengt) h(A

Fig«5 Spectru backscatteref mo d light neasecone rth d harmonics when YAG laser system bombards solid deuteriu hydroged man n targets*

(b)

Reflecte) Fig.(a 6 d scattere(0°d an ) d (45°) spectrf ao incident YAG laser, (b) Time sequence of backscattered light. 91 14*

Fig.7 Holographic interferometry (a) focused jus targen to t surface. (b) focused within target material at the depth of abou pm0 t.20 The second harmonic light of the main laser pulse is used for measurement. The pulse duration is 100 psec.

92 u=as

[^ electron plasma wave A

(resonance region) =sin9. (turning region)

focal spot -SOjum / target plasma

Fig.8 Outline of obliquely incident radiation.

93 PLASMA HEATIN INTENSY GB E RELATIVISTIC ELECTRON BEAM

K. Imasaki, S. Nakai, C. Yamanaka

Department of Electrical Engineering, Osaka University

Abstract

Intense relativistic electron beam generators have been constructed for the application of REB fusion research. The electron beam (300keV /lOkA) was generated and focused onto the target. The spotsize of the target determined by a 2-channel X-ray pinhole camer s smal mmexpandina 1 e s s .i aTh a l g plasma due to the pinched electron beam on a plain solid target was observe e streak-camerath y db . Pro e observatiomth f plasmno a expandin e heatingth g mechanis f densmo e plasm REy ab B seemo t s be due to the anomaly of the two-stream instability.

1. Introduction Recently intense relativistic electron beam (REBs ha ) become attractive in the field of research such as pellet fusio n) 1 , plasma heatin2) 3g) , plasma confinement and heavy ion acceleration concep e pellee Th .th f to fusioB RE y nb is similalasee th ro r t fusion . Comparing wit lasee hth r fusion, the main features of REB fusion are as follow, the generatoefficiencB RE e th rf y o ("-50%) coul muce db h higher tha ntotas it lase ld renergan y (*vMJ) coul muce db h larger. On the other hand, it is difficult to get short pulse of REB (/v nsec find )an e focusin incoherence th o lases t ga e rdu y electriane dth c beamchang e lattee th Th .f e o r disadvantage (long puls pood ean r focusing) coul overcome db usiny eb g larger pellet correspondin possible th o gt e large energf yo mose REBTh t* important proble fusioB RE f nmo which must 95 be investigated is the dissipation mechanism of the beam electro surfac e targee th th n nf o te o pellet absorptioe Th . n mechanism of REB energy in high density plasma is not so clea thas rlasea f to r. We have investigated focusin REBf go , plasma production and heating for the application of pellet fusion. We have constracted thre generatorB eRE s named JiiEIpEJI_ I,_ JJ^ItnJLJIJ^ REIDEN I was to develope fast high voltage technology. With REIDEN-ir we have investigated the performance characteristics of REB generator and the interaction mechanism of REB with solid target. REIDEN Jll is the scale up of II for the fundamental investigation of pellet fusion. In this report, we present the experimental result bj* REIDEN II.

2. Experimental Apparatus (REIDIN II) REIDE consisteI NI thref do e main components Mar,a x generato initiar rfo l energy storage ,coaxiaa l water insult- ed Blumlein type pulse forming line and a field emission diode with target schematie Th . c diagrasystee th s f mi mo shown in Fig.l. The stored energy of the Marx generator is transfere Blumleie th o dt n lin pulsy eb e charginge Th . foro t mBlumleid en e on n t wateline a fireth p s e i rga y d b the voltage pulse across the diode at another end. Intense electron bea generates mi fiele th dy d b emissio n from cathode connected to the center conductor of the Blumlein line. The Marx generator consists of 8 stage and its stored energy is 2.8K 400KVt Ja oute e Th . r conducto Blumleie th f ro n lins ei 1.7m long with 30cm of diameter. The inner conductor of the lin 1.5s ei m long with diameterf 10co m centes e i Th .e ron 1.5m long with 4cm of diameter. The storage energy of the 96 lin 0.6Kjouls ei e when charged voltag 300KVs e i chara e Th . - cteristic impedance of the Blumlein line was about 13 ft. pulse Th e transmission time lin e ofth e was lOOnsece Th . measured beam pulse length corresponded quite well to the designed value. The inductance of the isolating inductor between Marx generato Blumleid ran n lin 5pHs ei . This valu largs ei e enoug isolato ht Blumleie eth n line from Marx generator during the pulse formation.

The typical performance of REIDEN II are as follows Beam Current *- 2 OKA Beam Voltage /* 300KV Pulse Length ^lOOnsec Energy/Pulse /^- 0. 3KJ

3. Result 1 Diod3- e impedance The wave forms of the diode voltage and beam current are shown in Fig.2. The diode voltage is monitored by low-inductanca e carbon resistance voltage divider consisted of a potted assembly of 75 x 10ft, resistors* The beam curren measures ti resistee th y db r ring consistex 0 12 f do 10ft/ resistors in the return path. The time resolution of the voltage monitor is less than lOnsec. The resister ring has almost the same time resolution. From diode voltage and beam current wave form, the variation of the diode impedance is obtained, which is shown circlee byth Fig.3n si thin I .s cas brase eth s plain cathode of 30mm in diameter was used with 5mm of separation to brass anode pressure diode Th .th et e a chambe 0 torrabou1 s ri x .t1 ~4 97 In general the diode impedance can be described by the Child-Langumire relation. In early stage of the pulse the a* field emission comes from the protrusions on the cathode surfac thed ean n rapid vaporizatio ionizatiod nan e th f no protrusions takes hig o plact he currenedu t density?' This cathode plasma works as the virtual electrode. Therefore the diode impedanc decreases ei d from this plasma dynamics. Considering these effect impedance ,th plane-parallea f eo l diode consisting of a disk cathode of radius y and a diode gap d can be given by

where V is the voltage across the diode,eQ is the dielectric constant in vaccum, m is the mass of electron, e is the charge of election, u is the velocity of expanding plasma from cathode and t is the time after pulse beginning. From equation 1, the theoretical time history of the diode impe- Fig.3n i danc ) thin I gives .(b ei s s equacasns a i eo u lt 4 x 10 cm/sec which is reasonable velocity of this plasma. The experimental time history of the diode impedance shows gooa d agreemen equatioo tt . n1

3-2. Beam focusing and plasma generation. focuses REBwa d ont e targeoth t usin ga glas d 3mro sm n diametei r 10mm configuratio longe Th . e diodth s f ei o n shown in Fig. 5. The electron emxtt^d^rah tie cathode is pinched to e self-magneticentee th th y b r c s carriei fiel e d th dan o dt e plasmanodth n i ea generated froe glasmth s rod. 98 Phenomelogically the emitted electrons move along the glass rod surface '.

determino T focusine eth g spo ttargete sizth n eo / channe2 l X-ray pinhole camera utilizing absorbing foils of two different thickness was set. In Pig.4 the densitometer trace X-raf so y image alon polyethylene gth e target surfac showe ear n wit lOOyha m thic absorbere kB d an ) ,(1 with a 600y Be one, (2). In Fig.4, the region A corresponds to hard X-ray generation by bremsstrahlung of the beam electron and regioheatesofe e th th t n o B dX-rat plasmae ydu . From this observatio focae nth l spot targe e sizth RE f en o tB o was determined as small as 1mm or less. The maximum current density has been estimated to be more than 10 6A/c m2 with corresponding power density of 101 1watt/c m 2. i O The intense light generated frotargete mth , when electron bea linen mio bombar identifies se wa th , e dit b o dt polyethylenef o H d an o fC streae Th . k photograph beaf so m produced plasma were taken with two different orientations of slit. Photograph (a) alons ,surfac e wa targe e gth th f teo and photograph (b) was along the axis of the electron beam, as shown in Fig.5 The streaK photographs in Pig.5 show that the plasma produced by the pinched electron beam expanded only alon targee gth t surface. Whe targee n th exchange s twa d with copper the similar behavior of plasma was observed. Therefore observed expansion was not caused by the surface breakdown alon targee gth t surfacchargo t e edu building insulatine th un po g bea e anodth m y eelectronb . Figure6 shows the expanding velocity of the plasma observed by the streakcamera vs the acceleration voltage of the electron beam. ' 99 4. Discussion There are two possible mechanisms for the energy ransfer of the elecgron beam to the plasma : the collisional dissipatio collectivd nan e interaction wit plasmae hth e Th . energy loss of the beam electron by the collision and cerenkov radiatio gives n i ' y nb Q\

/2h) (2) •Kl/2)ZJln<3mcVkT

where rQ is the dassical electron radius, 2irh is the Planck's constant, n.^ is the target density, Z is the atomic number of the target material, Z. is the change state of the ions, T is the plasma temperature lighe th tv/cs s i i velocity c ,,3 ,

Y is the mass factor and XQ is Debye length. Retaining the first ter abovf mo e equation stoppine ,th g lengtgives i . nhX by \ _— «2 t~\ AIl O^, £•_e \^l where E. is the beam electron energy. If the total beam 6 energy which is given by / cchild- langmoir current is absorbed in the distance A. the plasma temperature T is given by etotal where s is the cross section of the pinched electron beam, n1 is the plasma density and k is the Boltzmann constant. Hence the expanding velocity v of the plasma due to plasma temperaturs i eT

vp ex: E (5)

As for the two stream instability the maximum linear growth rate a, in the case of cold plasma and cold beam, is 100 approximately give a=0.7(ny nb 2/n1) ' w e wherth s ei w

electron plasma frequency and n2 is the electron density of th instabilitee beath f mI ' . y induce dissipatioe sth f no

the beam, the decay distance A2 is given by

X2 = (ve/aHn(Ee/E0) (6)

where v is the electron velocity of the beam and EQ is the

thermal energy of the plasma. Substituting X2 instead of eqe .th (4 o A)dependenc.t e , th giveEs e ^i th y vnf b n e^ o o JL p 6

(7) In Fig. 6, the solid line shows the dependence of eg. (7) for the hydrogen of the polyethylene target and broken line is for Cu target. If the two body collision is assumed to be the heating mechanism, the interaction distance X, is one

orde magnitudf ro e larger thaXe 2.nth Thetemperature nth e becomes lowe rstreao thacastw e nf th meo instability.

6. Conclusion REB generato moderatf ro e size designe s REIDEwa I NI d and constructed. By using this machine, interaction^ of REB with high dense plasma has been investigated. The main results are as follows, Goo) 1 d correspondenc Blumleif eo n performanco et designe parameter was asertained. 2) The time history of the diode impedance showed gooa d agreement with plasma cathode theory. 3) The energy density of the beam was up to 10 11watt/c m 2, 4) The stronger interaction beyond the collision theor observeds ywa experimene Th . t result accorded quite well to the theory of two stream instability. 101 References 1) P. Winterberg Nuclear Fusion 12_ 353 (1972) 2) P.A. Mille at lre Phys. Rev. Letters3_ 8 (1973£95 ) 3) G.C. Goldenbaum et al Phys. Rev. Letters^ 830 (1974) 4) S.E. Graybill IEEE Transactio Nuclean no r Science NS-1 (19718 £43 ) 5) D.L. Morro l Appla t we . Phys. Letters 1 19(1971.44 ) 6) K. Imasaki et al J. Phys. Soc. Japan 37_ 881 (L974) 7) K. Imasaki et al J. Phys. Soc. Japan 38. 1554 (1975) publishee b o T NucleaYano. n l 6 di a ) t s8 e r Fusion • 9Buneiaa. )0 n Phys .3 (1959 Rev50 5 ).11

-mr Coaxial Blumlin line Marx Generator I -J Ml Diode. . Hate1 r GaIIp E-Beam W II -4HHP — 1 4 -| L m M

Fig.l The schematic diagram of the system.

102 100 ns/div 86 kV/div Diode Voltage

JU/ 100 ns/div 12,4kA/div Diode Current

Fig.2 The wave forms of the diode voltage and beam current.

100

Is 10

4. 100 10 0 5 ns

Fig.3 The variation of the diode impedance. 103 -B- -B—» (1) lOOpmBe (2)60C£mBe

1mm

Fig. densitometee Th 4 r trace X-raf so y image alone gth polyethylene target.

Tarcet t30mm (a)

Cathode 0 (c) 10

Fig. streae Th 5 k photograph diodd san e configuration,

104 150 200 250 300 Diode Voltage ( KV )

Fig.6 Expanding velocit observes yi streakcamerae th y db . experimentae th o l results using polyethylene target. experimentae th A l results usin targetu gC .

105 SOME REACTOR IMPLICATION LASEP SO R (OR RELATIVISTIC BEAM) FUSION

I. Spalding

UKAEA Culham Laboratory

ABSTRACT

The thermal stability of tamped cryogenic DT spherical-shell targets considereds wa shows wa nt i :tha t both black-body radiatio ambiene th d ntan vapour pressure withi innee nth r most operationan wala f lo l reactor could significantly modif geometre yth somf yo e type targef so t during their transit from the exterior to the centre of the reaction chamber. A "check- list somf "o e inertial-confinement reactor topics meriting examinatioy nb the Advisory Group was also suggested.

INTRODUCTION Some technological implications of the use of homogenous, spherical, pur targetT eD laser-igniter sfo d inertially-confined thermonuclear reactor applications have been discussed previously. The fractional mass-loss of such pellet sublimatioo t e sdu transin ni t fro cryogenima c "pellet factory" reactocentre e tth oth f eo r kepvessee b tn lquitca e small, i.e. ^ 3#, assuming pellet radii of order 10~a - 10 cm, working temperatures within the reactor vesse •£f l o 100 ambien, 0K vapoui tL r pressures

107 TYPICAL MULTI-SHEEP TARGETS Consider targets categorized as "Type IV" in Reference 5. Thermonuclear fuel is deposited on the inner spherical wall of a high Z shell, having inner and outer radii of R and R respectively. The fuel, having a well-defined inner radius R^ , may be cryogenic DT or a chemical compound such as lithium hydride. Table I summarises characteristic dimensions of two targets, A and B, inferred frotexte mth Referencef so sand5 respectively, 6 .

TABL Typica- EI l "Shell" Targets

TARGET "A" TARGE" T"B

Reference C5) (6)

R3 (pm) 1000 (Hig4 ~) 3. h Z ~ 40 (Pb or Au) ~ 15.9 (Solid DT) (Soli~6 5 ) dDT Laser Input 100 kJ 1 MJ Laser Pulse duration 3«5 x 10"* s (Gaussian FWHM) 10 s (Triangular) CT1> Thermonuclear 0/P 10MJ< ? (See Ref.?) 1000MJ Reactor Wall Radius ~ 1m -5m T. ~ 3.3ms ** 16.6ms

As discusse Referencn di e seem1t ,i s more convenien fabricato tt e eth pellet outside the heated structure of the reactor, and then to insert it (at high velocity) to the centre of the reaction-chamber. We shall conservatively assume that velocities of order 3 x 10s m/sec are practicable, noting that velocities approaching 10 m/sec would imply energies of order 1 ev per particle (i.e. far exceeding the DT binding energy) and a target movement exceeding 3itf #o s diameter durin time irradiatiogf th eo n (T^) timee Th .s Tu liste Tabln di thueI s represent reasonable estimate transie th f so t times centre toth reactof eo r chambers having inner (vacuum) wall radif io approximatel 5n>d an , yrespectively1 . 108 EFFECT OF REACTOR ENVIRONMENT ON TARGET

The ambient temperature OB) in the reactor is likely to lie within the range 560 - 10CXf K, irrespective of details of the reactor design (eg. lithium blanket or "dry wall" designs). Thus the black-body radiation intensity incident on a cryogenic target is of order^ 5«7 w/cm . A comparable heat flux will be produced by any vaporized lithium (or other gas) having a

pressure (PT-) ^ ^ Torr. These are the principle heat loads incident on the target; heating due to tritium 3-decay is by comparison completely negligible. What would be the consequence of complete absorption (3 = 1) of a 5»7 w/cm3 hea toutee loath rn d o surfac pellete th f eo ? One-dimensional thermal diffusion calculations are adequate for these thin-shell (high aspect ratio) targets, and some characteristic thermal penetration depth listee typicar sar fo Tabln di , leII target materials. Here,

AZ = 0.68 V K Tt (1) thermae th whers i l eK diffusivit materiale th f yo .

TABLE II - Approximate thermal penetration depths

MATERIAL AZ

T 3.3m= t s (Targe) tA Tt s 16. 6ms (Target B) Solid (normal)H *»00 pm 900 pm 8 Glass |J3 2 m 51 pm Au 900 pm 200m 0p

Compariso Tabld Tablan f showneo I I I e s that durin transiga t timf eo several milliseconds any temperature rise on the outer surface of the pellet will be rapidly conducted to the interior; indeed, temperature gradients of less than 0.4°C are required to conduct a heat flux of 5»7 w/cm through the shell materials of either Target A or B. The initial temperature rise of the solid DT is thus of order

f = <9 0.25 ([Ra - (2)

where <* is Stephen's constant and S and p are the specific heat and density of the respective shell materials. This temperature rise is sufficiently 109 rapid to melt the DT in either target. Numerical summation of the energy needed to melt solid H , raise it to its boiling point and subsequently vaporiz liquie eth d indicates thaeither tfo r target ove cryogenie r th 10 f $o c shell will evaporate; comparable numbers could be expected for DT, for which less cryogenic data has been published. Whether the black-body spectrum is fully absorbed by the pellet will, of course, detailedepens it n do d designoftes i t ni ;assumed exampler ,fo , that (anZ w dlo therefora e partially-absorbzng) outer ablative use e layeb dy rma to provide conductive "smoothing" of any non-uniformity of the incident laser pulse maie Th .n purpospresene th f eo t stres o nott significane s ei sth t impac reactoe tth r environment could hav cryogenin eo c target stabilitd yan design specifia s A . c example, Rudakov discusse thit da s meetine gth possibility of a 10 ° - 10iaJ thermonuclear output pulse being absorbed in 1 blankettonni L f eduto s hi ;ypulse cyclon ef eo ever second0 y1 s implies exceptional (and energy-consuming) pumping requirements if the ambient vapour pressure is to be held below 4- Torr. CONCLUSION Six questions summarize these and other reactor-related issues, which it would seem profitabl discuso et thit sa s Advisory Group. (1) A thermonuclear gain Q (fusion output/laser input) of 1000 was predicted in Reference 6 for a laser input energy of 1MJ, compared to gains of order 100 discussed in American work » _ « 'u j . The probable magnitude of Q determine credibilite sth inertial-confinemenf yo t approache civio st l power production; what are thought to be the major physics uncertainties in these various calculations? ) Apar(2 t frorelaxatioe mth laser-efficience th f no y requirement, whae tar the benefits of a fission-fusion hybrid? maximu e ) Whath (3 s ti m credible benefi derivee b o tt d fro successfuma l nuclear-pumped laser development? (4) Does direct H or CH fuel production (via 1^Mev neutrons), rather than electricity production via a conventional thermal cycle, significantly affec economice tth inertial-confinementf so ? doubln Ca e) (hig(5 shellhZ ) cryogenic targets (classified "Type Vn "i Ref. 5) actually be made with reasonable symmetry, and at realistic cost?

(Note that the gas filled targets discussed by Jonas and others, classification "Type III" of Reference 5, are thermally stable to the reactor environment, but claimee ar requiro dt e highly-shaped heating pulse maximur sfo m thermonuclear output ). 110 (6) Are cryogenic shell targets credible for high-repetition-rate reactor operation? (If not, what thermonuclear gains are predicted using chemically-bound, higher Z, thermonuclear fuel?)

) Spaldin(1 g I.J., "Laser Interactio Related nan d Plasma Phenomena", Schwar. Vol J (Plasm5 Hora. . .H H 77 z3B& p . , p a, Ed Press Yorkw ,Ne , 197*0. ) Breuckne(2 r K. , private communication, 1975* (3) Breuckner K. , Erice Summer School on Fusion Reactors (Sept 197*0 • (*0 Physics Today, Vol. 28, No. 3i pp17, (March 1975). (5) Fraley, P. S., et al. Fifth Conference on Plasma Physics and Controlled Thermonuclear Research, Tokio, Japan (197*0. Paper IAEA-CN-33/F5-5 (To be published). (6) Afanasev Tu. V., et al. JETP Lett 21, 68 (1975). (7) Clarke J. S., Fisher H. N., and Mason R. J., Phys. Rev. Lett 30, 89 and 249 (1973). (8) Nuckolls J., et al. Nature (London) 239 » 139 (1972).

111 LASER INDUCED NON-LINEAR PLASMA PHENOMENA (SELF PHASE MODULATION LIGHTF O ANOMALOUD )AN S ABSORPTIO RE F PLASMNN O B I A

C. Yamanaka

Osaka University, Institut Lasef eo r Engineering

Abstract The interaction between lase plasmad ran , such as mode conversiof no laser light to plasma wave, second harmonic generation at the resonance region (cut-off region), red shifted satellites with an isotopic effect in SHG-light and self-phase modulation of hack-scattered light from the turning region were discussed. Also the anomolous absorption of relativistic electron beam in plasma was shown which is interpreted by the two-stream instability*

Laser plasma interaction The interaction region is divided into two parts. One is the resonance region wher electroe eth n plasma wav trappes ei densita n di plasmaye welth f lo . (As shown in Fig. l). In this region the second harmonic is generated according to the matching condition 2 ^ ( O^e)«kt (2CO0) and K? («C$«0-hfct()- *t C2*>b wher wav e e ik frequencs e th stanet longitudinath r number, 1 s dfo i d yan O , C l and transverse waves reportes .A d befor thin ei s lasee caseth rf , i intensit y is larger tha parametrie nth c decay instability threshol satellitd re e dth e is observed with the shift of 2 <5frs . The plasma of hydrogen and deuterium shows the isotope shift red satellite which is due to the ion acoustic waves. The detailed selection rule was given at the Tokyo Conference [l], incidene Th t wave is reflected froturnine mth oblique gth regioo t e e ndu resonance. The spectrum of back-reflected light shows the broadening around the inciden tself-modulatioe lightth o t .e Thidu s si lasef no r e lighth y tb temporal chang densitf eo y induced fro ponderaootive mth e force. With absorption and charge separation electromagnetic wave is where of ~ f\&> is the density parturbation of the second order " 6J° '

*< where Htc *idensite sth zeroth-orderf yo ,

113 f /*•£ f** ° *>o V, J0 IT J J

A «fc *£ X" when the laser light is long, a steady density state gives

then A<40i8 proportiona— o lt This indicates that the blue shift is delayed from the red shift. The threshol sele th f f dmodulatioo face gives ni th t y nthatb wave *th e swelling rate near the turning region is faster than the ion .* propagation time over this region

This indicate s0 4*1 typicaa w/c 4z s a m l case* J- - 9.6 X

2 where laser power is 1 x loHf/cm | V^/c * S"* lO"** A i * l°~*t ^- * whole th e spectru ms shiftei e doppleth do t bluee re abouth du ,o £ t 6 t effect of the plasma expansion (1.8 x 10* cm/sec). The experimental results accord with the above prediction. ThcalculatioD eI bees nha n performe indicato dt temporae eth l change of the spectrum broadening. These results show the reasonable behaviour of self modulation.

Anomalous absorption of REB in plasma. The absorption mechanism of the HOB has been investigated. We found the new results due to two-stream instability. The beam total energy E. . _ is proportional to E •5/" 2, where B is the beam voltage. The classical absorbing distance is

whett Etotal -Sh where y\ . plasme isth a density and*s"i beae sth m cross section.

114 The plasma expanding velocity is given "by

two-streee th r fo s ma instability lineae th , r growth rate ( Q£O .? ) J wher e electroeth tZ.s i ^ n densit e beamth f *yo The dissipation length of the "beam is

then V