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Proceedings of the 1994 International Linac Conference, Tsukuba, Japan

SPALLATION SOURCES*

H. Klein Institut fUr Angewandte Physik der J. W. Gocthe-UniversiUil D-60054 Frankfurt am Main, FRG Abstract Principles of Neutron Sources

At present mainly two types of neutron sources arc in usc If high energy (e.g. 800 MeV) impinge on tlJe for neutron research, the steady state source based on target, tlley do not interact with the nucleus as a whole, but - fission reactors using highly enriched U235 fuel and the acce­ due to tileir short de Broglie wavelength - with the individual lerator based pulsed source, where the arc produced by , creating an intranuclear cascade inside tile nucleus; spallation of a nonfissile target. Several high intensi ty some high energy (secondary) neutrons and protons escape spallation sources arc under consideration nowadays, and these from tlle nucleus producing similar ca<;cades in neighbouring proposals as well as the existing machines will be reviewed. nuclei. The nucleus is left in a highly and relaxes Besides the general layout of the facilities the problems of the mainly by evaporating low energy neutrons. The high energy high currentlinac part will be shortly discussed. neutrons are of no use, but the others, produced eitlJer by evaporation or directly by the incident protons, can be slowed down to thennal (or - for time of flight experiments - epi­ Introduction tlJennaI) velocities by optimized moderators. This optimi­ h"ltion is not possible Witll reactors, since a special moderator Neutrons are very well suited to study the microscopic layout is needed to sustain the chain-reaction. The energy properties of matter by scattering experiments. This is due to dissipated in tile target per produced neutron is much smaller the physical properties of the neutrons, especially to its by spallation tllen by fission ('" 30 MeV for 800 MeV primary electrical neutrality, which allows for deep penetration into the protons compared to '" 200 MeV) leading to a lower power samples with only small damages. Together with its spin, its load in spallation sources. The number of neutrons produced magnetic moment, and the low absorption cross section, by protons depends on energy, target geometry and can probe the bulk properties of maller and target material. For a cylindrical Pb-target (0 = 10 cm, L = 60 its dynamics, fluctuations of liquids, the structure of polymers, cm) the yield Y [neutron/s] is given by: magnetic materials, biologieal samples, high T c superconduc­ tors etc .. By slowing down fast neutrons by moderators to Y= I4.2·I016(E-0.12)·I tllerrnal equilibrium the proper de Broglie wavelength according to tlle interatomic distances of some 10-10 m can be achieveD. witlJ E = proton energy [GeV], I = proton current [mAl. Research reactors - especially tlle high flux reactors at 0.12 GeV is the threshold energy. For 800 MeV one proton Brookhaven, at Oakridge, at ILL in Grenoble and at Saclay - produces about 15 neutrons; in case of depleted U238 tlJe fast and spallation sources serve a, sources for neutron scattering. fission processes contribute considerably to the number of The reactors operate in a more or less continuous mode, and arc neutrons ('" 25 instead of 15). The useful for often mainly used for malCrial testing and production. scattering experiments depends on tlle target and tlle moderator. Most of the present research reactors arc old, and tlleir life time The choice of tile proton energy is a crucial point. Fig. I [2] will end within the next two decades. It became very difficult to gives tlle dependence of neutron production on energy, Fig. 2 bui~d new reactors in the last time: The safety aspects (highly [3] tile dependence of neutron production nonnalized to tlJe ennched fuel) and the great public concerns require a more and beam power as function of energy. Above 1.3 GeV the produc­ more increasing time to get a license; in many countries new tion rate for a given power is nearly independent of the proton reactors can not be realizctl for political reasons at all. energy. From the target side energies ranging betwccn 0.8 and A way ou t of tlJe lack of neutrons arc tile spallation sources, 3 Ge~ or somewhat more are acceptable. For accelerators high which arc of intrinsic safety - they consume more energy than energIes are of no principle problem, whereas current limits they produce. They generate the neutrons by intense high exist, depending on energy. As a general rule, tile most econo­ energy proton beams which strike a heavy metal target. They mic solution is given by a layout, where tile maximum cur­ offer the possibility to pulse the neutron flux (Pulsed rent limit is utilized, which to a corresponding low ener­ Spallation Source, PSS), which is important for time of flight gy. Two main schemes are used [or tlle accelerator part: short experiments. They can produce tile same neutron fluxes or even linac plus rapid cycling synchrotron (ReS) and long Iinac plus higher tllan reactors, which arc already on tileir limit of compressor rings; botll delivcr tile required short pulses of '" 1 tolerable power density in the core. First proposals for J..lS on tlle target. The ReS demands for high energies and low spallation sources have been made already in the Sixties [1]. So c~rrent, for tlle pulsed linac witlJ accumulator rings it is just far only four spallation sources are in operation, but about ten vIce versa. For example: Proposals for a 5 MW solution look proposals arc being discussed. 'work partly supported by BMFT and KFA liilich for 3.6 GeV ,1.35 mA (ReS) or 1.4 GeV, 3.8mA (Linac).

322 Proceedings of the 1994 International Linac Conference, Tsukuba, Japan

in pulse (pulse lengtll ~ 500 Ils) with a repetition rate of 150 y 50 Hz; the 50 Hz synchrotron with a circumference of [nIp) 163.4 m accelerates up to SOO MeV, the circulating current is 10 A, tlle peak intensity 2S1013 protons per 0.4 IlS pulse; 100 injection is done by foil stripping. Upgrading from 200 to 300 IlA average is planned by a new rf-system of the synchro­ tron (doubling the frequency), and an improvement of the linac 50 by substituting tlle hv-injector by a RFQ (in cooperation with Frankfurt). The spallation source at Los Alamos uses the SOO MeV linac (LAMPF), then the beam is compressed into 0.27 Ils o~~--~--~--~----~~~----- 2 3 I. 5 (j 7 8 proton energy [GcY) long pulses by an accumulator ring (90.2 m in circumference) 13 Fig. 1: Neutrons poduced by an incident proton as Junction oj with a peak intensity of 5.10 p/pulse and an average power proton energy /2J of SO kW. Plans exist to extend this system in two steps, leading to 1 and 5 MW respectively by changing the front end 2.50 r-r,....,..,...,..,....,..,....,..r'T"" ...... ,.- ...... ,...... ,...... ,,....,..,,...... ,,...... ,,...... ,..,...,, of the linac (RFQ, new 400 and SOO MHz DTL's, funneling), *1014 n/s improving the CCL and adding up to three compressor rings. ~ ~ zl!: 2.00 QW Proposals and Studies for New Spallation Sources

The spallation source SINQ at tlle PSI in Switzerland is a o..al~~ 1.50 special case, because it is based on the existing 600 MeV iso­ i; chronous S-sector cyclotron. By improving the accelerator WI!: system from originally 100 IlA to the present 1 rnA and ZW 1.00 ....,,0.. further upgrading to 1.5 rnA a very powerful beam of 0'"' 0.9 MW will be achieved and will produce a neutron nux of I- 2.10 14 n/(cm2 ·s) with a Pb or Pb-Bi target. Due to the cw O. 50 L...I...... '-..L ...... L....I...... L-I...... &....o..JL...... '-'-'...L< ...... ~-'-"...>....L.J operation of the cyclotron, this neutron nux will be o 500 1000 ,500 2000 2500 3000 3500 continuous like in a reactor. SINQ shall be operational as PROTON BEAM ENERGY (MeV) soon as 1996. Fig. 2: Neutrons produced as Junction oj proton energy Jor a can· For the high power proposals the linac energy has been stant beam power oj 1 MWand a cylindrical tar· generally increased to 0.4 - 1.5 GeV, since tlle current limits get 1 m·diam x 1.5 m.long [3J ~3.y3. ····~-~-~··~- of rings are proportional to Synchrotrons or Com· At Argonne, lPNS-Upgrade is proposed; in fact it is more I LlNAC pressor Rings (~ 50 Hz) then an upgrade, providing 1 MW with one RCS, 2 GeV, 30 Hz, using all the experience of IPNS. At BNL a 5 MW PSS is discussed with two 3.6 GeV RCS's. An even higher energy of 10 GeV is foreseen in the ANS study of the INR H'· Source Moscow to decrease the radiation danlage of the first wall and so improving the reliability of tlle target. AUSTRON is a project of seven countries (A, CS, H, I, long pulses (~ 1 ms) PL, Slovenia, Croatia) with the assistance of CERN. It com­ bines a spallation source with a light ion cancer therapy Fig. 3: Genera/layout oj a pulsed spallation facility. Fig. 4 shows the layout. The 70 MeV linac injects There are other ideas for PSS's, based on the FFAG [4], on into a 1.6 GeV, 25 Hz synchrotron, which delivers IllS the induction linac [5] or on accelerators [6], which are pulses to the target (102 kW average beam power). Raising not considered in this paper. the linac energy to 130 MeV (second step) increases tlle cur­ rent limit at injection by a factor of 2, doubling fue repetition Existing Spallation Sources frequency to 50 Hz (tllird step) would finally result in a power of 410 kW. The light ions are expected to have an intensity of So far only four spallation sources are in operation with 109 part./s at a maximum energy of 400 MeV/nucl. They proton energies of 500 MeV (Argonne, KENS) or SOO MeV have their own low energy linac part, but use fue same main (ISIS, LANSCE) (see Table 1). The first three ones start with linac. The injection into fue RCS is complicated since it com­ 40-70 MeV H'-linacs which are followed by a synchrotron. bines injection schemes by charge exchange for tlle H'-beam The most powerful source is ISIS, witll an average power of and a classical one with fast kicker and septum for fue light 160 kW on target. The linac provides an H'- current of 20 rnA ions.

323 Table 1: Survey of existing and planned spallation sources and their main parameters

Name, Locat ion, Accelerator average aver. curr. Linac duty rep. rate pulse length current energy of p per Ref.

Status Energy power on on target cycle, on target dur. pulse one pulse pulse Japan Tsukuba, Conference, Linac International 1994 the of Proceedings target Ipeak on target ======lPNS, Argonne 50 MeV H- Linac 7.5 kW 15 J.1A 0.3% 30 Hz 0.1 !-Is 5 A 0.25 kJ 3*10'12 [7 J USA; operational 500 MeV RCS 5 rnA

KENS- I, KEK, Japan 40 MeV H- Linac 5 kW 10 J.1A 0.1% 20 Hz 0.05 !-Is 10 A 0.25 kJ 3.1*10'12 [7,8 J operational 500 MeV Synchr. 10 rnA

ISIS, RAL, Appleton 70 MeV H- Linac 160 kW 200 J.1A 1% 50 Hz 0.45 !-Is 10 A 3.2 kJ 2.5*10'13 [7,9,10 J UK; operational 800 MeV Synchr. 20 rnA

LANSCE, Los Alamos 800 MeV H- Linac 50/80 kW 60/100 I!A 10% 12/20 Hz 0.27 !-Is 18.5 A 3.9 kJ 3*10'13 [7,11J USA; operational storage ring 17 rnA

SINQ, PSI, CH 590 MeV cyclotron 900 kW 1. 5 rnA cw [7,12 J 1996 operational

NCNR, Los Alamos 800 MeV H- Linac 1 MW 1.25 rnA 7.2% 20/40 Hz 0.5 I!s 41.6 A 16.6 kJ 1.3*10'14 [13,14J USA; design study accumulator ring (5 MW opt) 30 rnA (2 targets) 324 ANL, lPNS-Upgrade 400 MeV H- Linac 1 MW 500 J.1A 2.5% (* ) 10 / 30 Hz 0.3 !-Is 53.3 A 32 kJ 1*10'14 [15,16 J design study 2 GeV RCS 33 rnA (2 targets)

PSNS, BNL, USA 600 MeV H- Linac 5 MW 1. 35 rnA 2.8% 2 x 30 Hz 1.3 !-Is 34.5 A 160 kJ 2.8*10'14 [17,2J feasibility study 2 x 3.6 GeV RCS 100 rnA (RCS, 2 targets 40/10 Hz)

ANS, Moscow, Russia 1 GeV Linac 4/1 MW 0.4/0.1 rnA 5% 40/10 Hz [18J feasibility study 10 GeV RCS (2 targets)

AUSTRON I, Austria 70 MeV H- Linac 102.5 kW 63 J.1A 0.25% 25 Hz 1 !-Is 2.5 A 4 kJ 1.6*10'13 [19,20 J design study 1. 6 GeV RCS 30 rnA AUSTRON II 130 MeV H- Linac 205 kW 125 J.1A 0.33% 25 Hz 1 !-Is 5 A 8 kJ 3.2*10'13 1.6 GeV RCS 40 rnA AUSTRON III 130 MeV H- Linac 410 kW 250 J.1A 0.65% 50 Hz 1 !-Is 5 A 8 kJ 3.2*10'13 1. 6 GeV RCS 40 rnA

KENS-II, KEK, Japan 1 GeV H- Linac 200 kW 200 J.1A 3.3% (* ) 50 Hz 0.2 !-Is 20 A 4 kJ 2.5*10'13 [8,21 J planned as JHP-part compressor/stretcher 20 rnA

ETA-based SNS, Japan 1.5 GeV p (H-) Linac 15 MW 10 rnA 10% 100 Hz 1 ms 100 rnA 150 kJ 6.3*10'14 [22J f eas ibi li ty study (compressor) (2 MW) (1. 3 rnA) (50 Hz) (40 kJ) (1.6*10'14)

ESS, EC 1.334 GeV H- Linac 5/1 MW 3.8 rnA 6.6% 50 / 10 Hz 1 !-Is 75 A 100 kJ 4.7*10'14 [23,24] design study 2 x compressor 100 rnA (2 targets) (2 rings)

(*) : 60% chopping effiency assumed Proceedings of the 1994 International Linac Conference, Tsukuba, Japan

H - Linoc normal or supe-rcoodudlng Negalive 70 MeV high @neI"gy structur~ drifl-lube SMW.1.334 GeV. SO Hz. o IOn source de ::=. 6.6 'I., t = 1.1. msec Upgrade of Chopper Itnac 10 130 MeV • 3.8mA Dump 1 • 100 mA 1 RrQ I Debuncher ",~--,,:-...:t:..::~. ~s::'"

r :1.9 mA i - 100A

Lighl Ions ECR RFQ for /~~- Itghl.-ion lighHons - _R&D line source , , Spalla- lion '\targel 2 l . = 600 nsec Dump 'Y, rev 'voids' 240 nsoc './ pul .. length: 360 nsoc '(X)() turn InJKtion circumference _ 163 m

Fig. 4: Proposed layout for the A USTRON PSS with the additio­ nal light ion input line for the cancer therapy facility -----

In Japan the so called KENS-II PSS as an important part of the Japanese Hadron Project (Fig. 5) is proposed. A 1 GeV, Fig. 6: Proposed layout and main parameters of ESS 0.4 mA H --linac feeds a compressor/stretcher ring (50 Hz), which allows for pulse lengths of 20 ns, 200 ns and 20 ms. The preliminary ESS-Iayout is given in Fig. 6. 5 MW In discussion is also at JAERI the construction of a very average power are achieved by a 1.334 GeV, 50 Hz linac fol­ powerful (15 MW) 1.5 GeV p-Iinac (10 mA average current, lowed by two compressor rings, which provide Ills-pulses. pulse length 1 ms, rep. rate 100 Hz) for tlle transmutation of The linac energy has been chosen to minimize beam losses at nuclear waste. This linac could be used as a next-generation injection; the HO particles behind the stripper foil are then 2 MW PSS, using H- ions and a compressor ring (50 Hz). mostly in an excited state with relatively long life time, those In Europe a two years study for a European Spallation Witll a short life time, preferably produced at other energies, Source (ESS) has been aproved by the EC now. A study group would decay into H - shortly after the foil, first captured, but has been established under the auspicies of a council in which then being lost in tlle ring [25]. The particle loss is tlle major nine member states of the EC are represented. problem in PSS's for hands on maintenance! For tile linac it should not exceed 0.4 nA/m. Two targets are foreseen with short pulses, a third target with 2 illS long pulses direct from Ion source Proton linac (1 GeV) the linac is possible. In the next chapter some problems of the RFQ (3 MeV, 432 MHz) Coupled-celilinac (CCl) high intensity linacs are discussed, taking ESS as an example. Drift tube linac (DTl) ((1 GeV, 1296 MHz) I I ( (150 MeV, 432 MHz) The ESS Iinac part

Compression/Stretcher This chapter is only a short overview, for more details see @M Ring (CSR) (24] and tlle references quoted therein. The scheme of tlle ESS . \ linac part is shown in Fig. 6. The beams of two lines with ion source, LEBT, two RFQ's witll a fast chopper in between

15

High Enc>rgy Lmoe sc: 7(1YkJ50 MHz Bur

'OJ~V- ~ t)LD~V Accumulator Rj~s. ® ISO MeV lnjK:lion by ~ W-slrippiny Il. Fast Cho~( I _1OO1200/300mA t2r1"9s, 2-2,6.1.) PPP. jX'ok i .000j

Fig. 5: General layout oftlte Japanese Hadron Project (JHP) Fig. 7: Linac section. proposed for ESS

325 Proceedings of the 1994 International Linac Conference, Tsukuba, Japan

Table 2: Examples of parameters of the ESS-injector-RFQs

C"'P r----- RFQI RFQ2 or RFQ3 f [MHz] 175 175 350 Dumpng ------~---r------~>;fL---,.lJ:::4.. tub. Tin [MeV] 0.05 2.0 2.0 190' bond) Tout [MeV] 2.0 5.0 (7.0) 5.0 (7.0) L [m] 2.9 5.5 2.9 Hole for sparking Ground ~[kWJ 350 700 350 plug el6c1roOo N beam [kw] 100 150 150 I limit [mAl 100 100 200

Evcn for tllC relievcd requirements there is no ion source available at tlle moment, which provides tlle necessary para­

mcters at tlle same time ( 70 mA, Erm, ~ 0.1 1t mm mrad, Fig. 8: Schematic drawing of the HIEFS-source with extraction pulse Icngtll 10 ms, 50 Hz rep.rate, high reliability, long system 129J under test for ESS lifetimc). Bcst candidates so far are the volume sources deve­ loped in Berkeley [26, 27J and Culham [28J. RFQ2 In Frankfurt we have designed a source based on the HIEFS 175 or 350 MHz [29] with a longitudinal magnetic field and RF excited plasma (Fig. 7), first experiments will be done in the next months. The LEBT has to transport and to focus the beam into the DTL 350 MHz RFQ; electrostatic and magnetic (2 solenoids) solutions are under consideration, taking into account space cbarge decom­ te---- 2.5rn---~ pensation and its rise time, nonlinear external and self field, emittance growtll etc. [30]. Thc first RFQ opcrates at 175, tlle second with 175 or 350 MHz (Tab. 2), botll are not state of tlle art [31, 32, 33, 24]. Chopping is necessary to produce 240 ns long voids in the Fig. 9: Funneling-section. proposedfor ESS; D: if-deflectors beam for clcan injection and ejection into and from the rings. 175 MHz. S: septum-magnet, T: triplett, B: buncher cavity Funneling [34] can be achieved by bending magnets and rf­ 350 MHz dcflcctors and rebunchcrs (Fig. 8). The main problems are tllC rf input rf input rf-cavitics (preferable IH-structures) and thc proper electrode \ Nb \ two-cell geomctry for emittance preservation. Thc drift lube linac (350 MHz, L = 75 m, cavity peak power = 13 MW) has to accelerate from 5 (or better 7) MeV to 150 MeV. It is in principle state of the art, a post coupled input Alv,ucz structure has been considered so far, but a bridge or II--t--t-- coupler cavity couplcd DTL or an IH-structurc are also possible gate valve structures. o m The high energy linac will accelerate to the final energy of 1.334 GeV and may be normal or superconducting. For thc __ tuning frame n.c. Iinac a frequency of 700 MHz seems to be appropriate, lcading to a peak current of 200 mA; but a frequency of 1050 ~~~~~ MHz is not out of discussion. As a first option we consider side coupled cavities as used at LANL or FermiIab; tlle new Fig. 10: Superconducting accelerator module, proposed for ESS SCC-linac at Fermilab serves as a good basis for the production techniques and cost estimations. An upgrade to the are funneled at 7 MeV and further accelerated by a DTL and a higher duty cycle of = 7 % seems to be no severe problem. high energy Iinac. Funneling is preferred since it reduces the re­ But otller structures like tlle DA W are in consideration also. quired current from the ion source in tlle space charge domina­ For reviews of structures see [35, 36]. An economic field ted part of the linac (70 instead of 140 rnA) tllrough the LEBT gradient is about 2.8 MV IIII, leading to Joule losses of about and the RFQ's. It facilitates by tllis the realization of tllese 100 MW peak in addition to the beam power of 70 MW peak. components, promises a better beam quality and allows for The linac length is about 570 m, the aperture radius 22 mIll. chopping between the RFQ's at a low frequency of 175 MHz. For more details and beam dynamics see [37J.

326 Proceedings of the 1994 International Linac Conference, Tsukuba, Japan

For a superconducting version a frequency of 350 MHz is [I I P. Tunnicliffe, G. Bartholomew, "Intense " in P. Lapostolle, A.Septier cd.: "Linear Accelerators", North 1I0lland, preferred at the moment. The optimum acceleration field is 1970, p. 1011 [2J A.Ruggiero, "Study of a Spallation Neutron Source based on Fast· about 10 MY/m (Qo 3.109, Qload 3105) leading to a much = = Cycling ·Synchrotrons", EPAC·94 shorter (",320 m) and cheaper Iinac [38). The large aperture of [3J Next·generation spallation neutron sources, Yol. II, Jan. 1993, 10 cm reduces the non linear field components near tlle axis; Los-Alamm, NM, USA; LA·UR·93·4440 [4 J S. Martin, E. Zaplatin, P. M""ds, G. Wustefeld, K. Ziegler, "Study of this will reduce the emittance growth and tlle particle losses in an FFAG Synchrocyclotron for a Pulsed Neutron Source", 13. Int. the structure. Due to the pulsed operation (the pulse lengtll is Conf. on Cyclotrons and their Applications, Yancouver, July 1992 [5J W. Barletta, A. Faltens, E. lIenestr07Al, E. Lee, "High Current fixed by the 1000 injection turns allowed maximum) tlle s.c. Induction Linacs", LY ·94 Iinac looses a part of iL~ intrinsic efficiency by tlle long build [6J A. Krasnykh, "Conception of e"Beam Driven Subcritical Molten Salt Ultimate Safety Reactor", LY·94 up time in the order of 0.5-1 ms, which has to be taken into [7J I.S.K. Gardner, "Review of Spallation Neutron Sources", Proc. of the account. Fig. 10 shows an accelerator module. Witll one rf­ 1988 European Conf., June 7·1 1,1988, Rome, p. 65 coupler only a two cell structure is fed, and even tllen tlle [81 N. Watanabe, H. Ikeda, "Status Report of the KENS Facility", ICANS­ neccessary power per rf-window with 400 kW is much larger XII [9J N.D. West, "Performance of the 70 MeY Injector to the ISIS than the power that can be handled nowadays (150-200 kW); Synchrotron", ICANS·XII p. A·85 therefore developments to improve tlle couplers are going on [IOJ I. Gardner, "ISIS Status Report", EPAC·94 [I I J M.T. Lynch el.a!., "Linac Design Study for an Intense Neutron·Source at several places. Of course one could reduce the accelerating Diver", Proc. of the 1993 Particle Accelerator Conf., May 17·20, field, but then the s.c. linac will loose some of its advantages. 1993, Washington, p. 1683 [I2J G. Bauer, "Die Spallationsneutronenquelle SINQ", PSI, Yillingen, CH Other concerns connected witll tlle low frequency and tlle high [I3J R. Pynn, "Plans for a New Pulsed Spallation Source at Los Alamos", electric field are the detuning by tlle Lorentz force and tlle dark ICANS·XII p. P·7 [14] A. Jason, R. Woods. "The Los Alamos Study for a Next·Generation currents. In both cases a higher frequency (700 MHz) would Spallation-Neutron·Source Driver", EPAC·94 help, but possibly cooling with supernuid Helium at about [I5J D.S. Drown et.a!.,"IPNS Upgrade· A I MW Spallation Neutron Source", ICANS·XII p. P·I3 2 K might then be neccesary due to tlle increased rf losses. In [I6J Y.Cho et.a!., "Conceptual Design for One Megawatt Spallation any case, the use of superconducting cavities is very promi­ Neutron Source at Argonne", ICANS·XII p. A·57 [I7J L.N. Blumberg, "Preliminary Report on the BNL Spallation Neutron sing, but needs further investigations. Source Design Study", ICANS·XII p. A·20 [18J Yu. Ya. Stavissky, Yu. Y. Senichev, "Advanced Neutron Source for Physical Research", ICANS·XII p. P-36 Conclusions [19J II. Schonauer, "AUSTRON . a Spallation Neutron Source for Central and Eastern Europe", ICANS·XII p. P·26 [20J Ph. Dryant, CERN, private communication Many proposals for future pulsed neutron spallation sources [2I} N. Watanabe, private communication are in discussion worldwide to overcome the increasing [22J N. Watanabe, "An intense Pulsed Spallation Neutron Source ll,ing a High·Power Proton Linac for ", ICANS·XII p. shortage of high nux neutron facilities. Two solutions, name­ P·21 ly the combinations of high energy linacs witll compressor [231 II. Lengeler, "Proposals for Spallation Sources in Europe", EPAC·94 [24} II. Klein, "Linac Design for the European Spallation Source", LY·94 rings or of linacs with low energy and rapid cycling synchro­ [25J G. Recs, "Injection", Proc. of General Course of CERN Acc. School, trons, are mainly in competition. The R&D activities for CERN 94·01,1994, p. 737 [26] A. Anderson, c.F. Chan, K.N. Leung, L. Sokora, R.P. Wells, "Low­ tllesc high intensity accelerators are also of great interest for energy injector design for SSe", Rev.Sci.lnstr. 63(4), April 1992 several other projecl~ like energy production, radioactive waste [27J K. Leung, "RF·Source Operation for Production of H+ and H· Beams", LY·94 trans-mutation, material irradiation test facilities, or inertial [28J R. Mc Adams, R.King, G. Proudfoot, A.Holms, "Pure and Cesiated fusion. CW Yolume Source Performance at the Culham Ion Source Test Stand", AEA Technology, Culham Lab. [29J K. Yolk, W. Barth, A. Lakatos, T. Ludwig, A. Maaser, H. Klein, "A Acknowledgements compact for RFQ injection", Proceedings of the EPAC·94 [30J P. GroB, J. Pozimski, R. Dolling, T. Weis, II. Klein, "bp. and Theor. I nvestigations of Emmitance Growth of Space Charge Compensated I want to thank all colleagues who kindly provided Beams in a Magnetic Transfer Line", this conference. [3IJ A. Schempp, "RF Quadropoles as Accelerators", in: "Advances of informations, documents, and actual data. For support and Accelerator and Technology" (ed. II. Schoppcr), World great help in finishing this paper I express my sincerest Scientific, Singapore (1993), p. 194 [32J D. Deitinghoff, "First beam dynamics calculations for the ESS·RFQs", gratitude especially to H.-W. Glock and H. Deitinghoff, Int. Rep. 94· I I, lAP FFM C. Peschke, 1. Pozimski. [33J J, Klabunde, E. Malwitz, J. Friedrich, A. Schempp, "Upgrade of the IlLI·RFQ Accelerator", this conference [34J K. Bongart, "Funneling", ESS-Linac Meeting, Sept. 1993, Frankfurt References [35J Y. YamalAlki, "Recent technological Developments in Accelerator Structures", Linac 92, p. 580 [36J G. Lawrence, "Critical Design Issues of High Intensity lIadron (Proc. of the Twelfth Meeting of the International Linac,,", EPAC-94 Col/abo ration on Admnced Neutron Sources 24 . 28 May 1993, [37] M. Pal"t, K. Bongardt, "Design Considerations of the ESS CCL", this conference Abbingdon, UK is referenced as leANS·XII; Proc. of the 1994 [38J H. Heinrichs, H. Piel, Univ. WuppertaI, ESS Meeting, Febr. 1994, European Accelerator ConJ, London, UK, 1994, to be published Julich, and private communications. is referenced as EPAC·94; Int. ConJ on Accelerator Driven Transmutation Technologies and Applications, Las Vegas, July 1994, Am. Inst. of Physics Press is referenced as LV·94.)

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