LA-651 O-PR PROGRESS REPORT 11– UC-21 Issued: November 1976 c. 3 CIC-14 REPORT COLLECTION REPRODUCTION COPY I n = Fusion Program _ .. ~— -- -11 —June 30, 1976 los~alamos scientific laboratory of the University of California LOS ALAMOS, NEW MEXICO 87545 /\ An Afllrmotive Attic.n/Equctl Oppc.rtunity Employer UNITED STATES ENERGY RESEARCH AND DEvELOPMENT ADMINISTRATION CONTRACT W-740 S-ENG. 36 The four most recent reports in this series, unclassified, are LA-5739-PR, LA-59 19-PR, LA-6050-PR, and LA-6245-PR. This work was supported by the (JS Energy Research and Development Adminktra- tion, Division of Laser Fusion. Printed in the United States of Amenea. Availablefrom National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfield, VA 22161 Price: Printed Copy $6.00 Microfiche $3.00 ‘ml, rrp..t m.. prrp.rcd. .caw.t d work.v.mn.rrd b. the t,.imd St.w. (;.v.rnme.t, Wtthw the (,rdwd St.!.s nor !he (’nited.S1-1- K.rre Re... rt h .nd [)...1. tn.nt Ad. mini,t,. tier... or their.mplqtrs. nor..> 0[ theirco.. trwtom. wbw.trwtor.. or their emplu,crs. m.kes ● y w.rr. nlv. .zw.” o, implied.o, .s.umti .nv 1.s.1Ii. hllll, or resw..ihllity rut the.ccur.m. complaenes..or useful.”. of .nw i.r.rm.tio.. .pp.r.t.s. product.or processdlsc!owd.or reprc.eql. th.1 it. would .ot I. fting. prlv. teh ow.rd ,ishl.. CONTENTS Abstract 1 Summary 2 I. C02 Laser Program 10 Single-Beam System (S6S) 10 Two-Beam System (TBS) 12 Eight-Beam Laser System 16 High-Energy Gas Laser Facility (HEGLF) 20 C02 Laser Technology 35 II. New Laser Research and Development 56 Introduction 56 Experimental Studies of Rare Gases and Rare-Gas Oxides 56 Metal-Vapor Lasers 61 Theoretical Support 65 Optical Damage Studies 71 III. Laser Fusion -- Theory, Experiments, and Target Design 75 Wavelength Scaling in Laser Fusion 75 Target Experiments at 1.06 and 10.6 pm 78 Theoretical Studies of Laser Fusion 84 Target Design 90 IV. Laser-Fusion Target Fabrication 93 . ‘-==roduction 93 w. High-Pressure DT Gas-Filled Targets 93 ;* ;0 ‘- Cryogenic Targets 98 ‘m V. Target Diagnostics 101 : -;:=: [ 101 y:~ Ol;:oduct~Ont:cal Diagnostics of C02 Laser-Produced P1asmas 101 .- - .. — -–—— :m Interferogram Analysis 102 I_ I_~. X-Ray Diagnostics 103 ‘m~ Automatic Laser and Target Data Acquisition 107 -. Etch-Track Ion Diagnostics 109 Calorimetry 109 Target Alignment Systems 109 VI. Applications of Laser Fusion -- Feasibility and Systems Studies 111 Laser-Fusion Reactor and Electric Generating Station Concepts 111 Hybrid Reactor Concepts 119 Synthetic Fuel Production from Laser Fusion 120 Experimental Investigation of Imploding Shell Stability 123 Experimental Oetermination of Materials Property Oata 123 iii VII. Resources, Facilities, and Operational Safety 124 Manpower Distribution 124 Facilities 124 Operational Safety 124 VI I. Patents, Presentations, and Pub”ications 125 Patents Issued 125 Presentations 125 Publications 128 iv LASER-FUSION PROGRAM AT LASL January 1 – June 30, 1976 by Eugene Stark and the Laser Division Staff Edited by Frederick Skoberne ABSTRACT Progress in the development of high-energy short-pulse C02 laser sys- tems for fusion research is reported. The Single-Beam System continued to be used in target experiments at a peak intensity of 7 x 101” W/cm2, and the system was improved. The status of the Two-Beam System, on which target experiments have begun with 300-J, l-ns pulses in one beam, is described. Construction and checkout of the Eight-Beam System is continuing. Further design studies for the High-Energy Gas Laser Facility and the initiation of a prototype program are reported. The rare-gas oxides and dimeric mercury were emphasized in investiga- tions into new lasers for fusion research. Experimental kinetics studies, a study of heat-pipe containment of metal vapors, theoretical support, and optical-damage investigations are described. Significant experimental and theoretical results are reported on the question of wavelength-scaling in laser-plasma interaction physics. Stud- ies of vacuum insulation as a means of preventing target preheat by hot electrons are also summarized. Analyses of the ponderomotive force in laser-plasma interactions and of the relationship between x-ray spectrum and suprathermal electron distribution are described. Improvements to the MCRAD and LASNEX design codes are outlined, and a LASNEX analysis of a target heated by laser-generated fast ions is discussed. Improved methods of screening, characterizing, and fabricating microballoons and more com- plex targets are described, and progress in applying uniform layers of DT ice on the inside of a microballoon is reported. Improvements in diagnos- tics include x-ray streak photographs, the fabrication of x-ray microscope systems, and x-ray film imaging. New results in our feasibility and systems studies are presented, in- cluding the wetted-wall and magnetically protected reactor concepts, the effect of ionized debris on cavity walls, the fusion-fission breeder con- cept, and the production of synthetic fuels by fusion radiation. 1 SUMMARY AND PROGRAM OVERVIEW x INTRODUCTION several years, which have ignored such important effects as the laser ponderomotive force, our new The Laser-Fusion Program was established at results indicate that the laser absorption and the Los Alamos in 1969, with the initiation of research hot-electron spectra inside the target plasma are into high-pressure C02 laser systems. Within the very similar for 1- and 10-gm light at equal inten- next few years, we developed the electron-beam- sities. controlled C02 laser amplifier, and expanded our efforts into a complete, balanced research program of laser fusion for energy and military applica- ~2 ‘ASER ‘ROGw tions. Our long-range goal is the completion of a It is generally agreed that the high energies comprehensive set of experimental and theoretical (several hundred kilojoules), short pulse lengths studies to test the scientific and engineering fea- (0.25 tel. Ons), and smooth, focusable beams re- sibility of using laser-induced microexplosions of quired for laser fusion can be achieved efficiently small fusion pellets to produce heat for connnercial only by gas laser systems. Economical systems re- electric-power generation and other applications. quire large-aperture beams to avoid laser damage to Basic elements of this work include: ,the de- the optical components. Only gas lasers can oper- velopment of efficient, short-pulse, high-energy ate in such a large-aperture configuration. His- laser systems to illuminate small fuel pellets; ad- torically, the C02 laser has received major empha- vanced laser research; the design and fabrication sis in our development effort because of its high of fusion pellets; the conduct, diagnosis, and efficiency and its well-developed short-pulse gen- analysis of laser-target interaction experiments; eration and amplification technology. We have theoretical studies of the physics of laser-matter chosen a sequence of progressively more powerful interactions; and systems and applications studies. C02 laser systems, with each new system requiring a Significantly, our Laser-Fusion Program has reasonable extension of the state of the art while contributed to the initiation of other important providing the capability for important new target programs, ranging from a large laser-isotope sepa- experiments. Our existing and planned C02 laser ration effort and a joint development program with systems include the following. Union Carbide Corp.’s Y-12 plant on mirror fabrica- tion by micromachining -- expected to have a wide Single-Beam System (SBS~ impact on the optics industry -- to a small project This system includes an oscillator and four on basic research into photosynthesis. electron-beam-controlledamplifiers. Three ampli- Highlights of the past six months include the fiers were used in the first 10.6-um laser-target initiation of wavelength-scaling experiments at experiments early in 1973, delivering 10 J in a 7 x 10’4 W/cm* in the single-beam C02 laser system, l-ns pulse. Since then, the SBS has been upgraded and the start of target experiments at 300 J in a to generate 250 J in l-ns pulses and to deliver single beam in the two-beam C02 laser system. Re- 180 J to a target with a peak intensity of 7 x 1014 sults of these experiments, and related work on our W/cm*. The SBS also serves as a developmental test- Nd:glass laser system, have been compared with bed for new laser-system components, e.g., oscilla- theory and have led to a significant new under- tors, isolation schemes, and optical systems. Prog- standing of the wavelength-scaling question. In ress is summarized as follows: contrast to theoretical predictions of the past 2 ● Substantial upgrading of the fourth am- ● A major discovery was the fact that laser plifier was initiated. Power-supply modifications light reflected from the target creates a region of now permit reliable operation at a higher excita- optical gas breakdown in the amplifier, which then tion voltage resulting in significantly increased absorbs the reflected light. This absorption pro- output pulse energy. tects optical components earlier in the amplifier chain from the severe, damaging light intensities ● A spatial filter was installed in the that would otherwise occur. system to smooth the transverse profile of the laser pulses. This modification reduces “intensity spikes in the pulse profile, helping to prevent op- Eight-Beam System (EBS} tical damage to mirrors and windows, as well as in- This system will include an oscillator, pream- creasing the focusability of the beam. plifiers, and four dual-beam amplifiers, with a design-point performance of 10 to 20 TW in a 0.25- ● Target experiments were performed at a to l-ns multiline pulse (maximum energy output, 10 14 peak intensity of 7 x 10 W/cmz.