Overview of the EURISOL post-accelerator design and studies

Transcription

1 Overview of the EURISOL post-accelerator design and studies Patrick BERTRAND On behalf of the TASK 6 team First EURISOL User Group Workshop January 28, Firenze 1

2 Task 6 Team : EURISOL Post Accelerator TASK LEADER : Marie-Hélène Moscatello (GANIL,France) RFQ : A. Bechhold (Frankfurt University, Germany) O. Zimmermann (Frankfurt University, Germany) G. Bisoffi (LNL Legnaro, Italy) P.A. Posocco (LNL Legnaro, Italy) A. Palmieri (LNL Legnaro, Italy) A. Pisent (LNL Legnaro, Italy) Fast chopper : M. Di Giacomo (GANIL, France) G. Le Dem (GANIL, France) (Post-doc 1%) MEBT & LINAC : P. Bertrand (GANIL, France) J.L Biarrotte (IPN/Orsay,France) G. Normand (GANIL, France) (Post-doc 1%) 2

3 SUMMARY 1. Experimental requirements 2. General layout of the Post Accelerator 3. LEBT (Low Energy Beam Line) 4. RFQ (Radio Frequency Quadrupole) 5. MEBT (Medium Energy Beam Line) 6. LINAC 7. Safety Aspects 8. Conclusion 3

4 Experimental Requirements (from Task 1, N. Orr, April 26) 1. Maximum beam Energy - 15 MeV/u for the benchmak 132Sn - if technically feasible, avoid stripping 2. Minimum beam Energy - beams of energies below.7 MeV/u required, but not within the remit of task 6 ( task 1) 3. Energy Variability - finest possible change in energy should be possible - <.5% at energies < 2 MeV/u - 1 MeV/u at energies > 2 MeV/u 4. Beam Energy Definition - absolute value better than.1% (related to task 6 and task 1 work ) 4

5 Experimental Requirements (from Task 1, N. Orr, April 26) 5. Time Resolution - Time width (FWHM) :.5 ns ( 1 nsec acceptable) - 1 psec possible? 6. Beam Time Structure - 88 Mhz (dt=12 ns) is too high for many experiments - separation between pulses of 1-2 nsec required! - Chopping the beam between 1 nsec 1 msec required 7. Beam Sharing - strongly recommended to consider 2 acceleretors, fed by a different target-ion source station : (1-5 MeV/u and 5-15 MeV/u) 8. Stable beam operation - Operation of the post accelerator with stable beams also requested 5

6 Experimental Requirements (from Task 1, N. Orr, April 26) 9. Beam Purity - Single isotope beams are required ( beam preparation task ) 1. Beam Emittance and Spot Size - no exact numbers agreed on but : - emittance of 1-2 pi.mm.mrad mm**2 spot size 6

7 General layout of the Post accelerator Principle: LEBT from and with task 9: beam preparation RFQ(s) Normal temperature or/and super conducting MEBT with challenging fast-chopper SC LINAC with independently-phased superconducting RF cavities Why a SC LINAC? - Excellent efficiency - High transverse acceptance (low beam losses) - High β-profile flexibility: (wide range of Q/A ion can be accelerated) 3 independant post-accelerators: - very low energy (not studied here) - low energy (1 5 MeV/u ) - high energy 5 15 MeV/u for 132Sn25+ 7

8 General layout of EURISOL Driver RIB production Post-Accelerator Beam preparation Task 1 Task 9 Task 6 8

9 General layout of the Post accelerator BEAM 14 #154 #8 #27 #15? 9

10 Low Energy Beam Line transfer : LEBT (from Task 9 : P. Delahaye June 27) First hypothesis : 1+ beam energy variation V 1+ V1 1+ β constant! V n+ V2 n+ Initial design high intensity RFQ cooler and buncher 1

11 Low Energy Beam Line transfer : LEBT (from Task 9 : P. Delahaye et al. 1th January 28 (draft version)) Second hypothesis : n+ beam energy variation by decelerating cavity Target/ion sources V 1+ linac Bunching Bunching section (2) RFQs section 8MHz Linac V2 Decelerating cavity Lowresolution mass-selector Charge selector Charge breeder Decelerating cavity To low-energy areas V n+ 11

12 Low Energy Beam Line transfer : LEBT (from Task 9 : P. Delahaye et al. 1th January 28 (draft version)) Third hypothesis : RFQ on HV platform (P. Ostroumov, PAC 21) Target/ion sources V RFQ on HV Platform linac HV platform Bunching RFQ RFQs Lowresolution mass-selector Charge selector Charge breeder Linac To low-energy areas V 12

13 Normal conducting RFQ : MAFF RFQ INJECTOR (RFQ team from Frankfurt University ). MAFF RFQ Injector under testing at the MAFF test stand. New NC RFQs for EURISOL under design, based on the MAFF technology length frequency m/q Voltage Q-value Shunt impedance W in W out 3 m 14 MHz kv (9.5 kv *m/q) kω*m 2.5 kev/u 3 kev/u MAFF RFQ LEBT tank Steerer Quads ion source 13

14 SC RFQ : Legnaro TESTS on PIAVE INJECTOR (RFQ team from INFN Legnaro ) The superconducting RFQs in LNL are now in operation on the PIAVE injector EURISOL NC/SC RFQs under design. PIAVE Energy at the end of PIAVE Transverse emittance measurement ε norm x RMS (mm.mrad) LNL PIAVE RFQ ε norm y RMS (mm.mrad).58 MeV / u 1.2 MeV / u

15 Normal conducting EURISOL RFQ 1 (P.A. Posocco, Legnaro, 7th January 28) Frequency Ion m/q Input energy Output energy Max suf. E Field B Length 88 MHz 7 5 kev/u 88 kev/u ~18 MV/m (1.8 Kilpat.) 7.2 ~3m Emittances (1k particles, 1% transm.) t. norm. RMS (mm mrad) longitudinal RMS in out MeV Deg mm mrad

16 Super conducting Eurisol RFQ 2 (P.A. Posocco, Legnaro, 7th January 28) Frequency Ion m/q Input energy Output energy Max suf. E Field B Length 88 MHz 7 88 kev/u 56 kev/u ~25 MV/m 4.5 ~2m Emittances (1k particles) t. norm (mm mrad).1.15 growth 1% 2% transm 1% 1% with an uniform longitudinal distribution, φ=15.2 4% 99.6% E=.3MeV 16

17 8.8 Mhz Buncher + NC RFQ + SC RFQ principle (P.A. Posocco, Legnaro, 7th January 28) CW injection system 8.8 MHz Chopper 8.8 MHz Buncher 3m Rebuncher 2m cryostat NC RFQ SRFQ 5 kev/u 88 kev/u 56 kev/u Lenses 8.8MHz bunching 17

18 Performances of the NC RFQ with bunched beam (P.A. Posocco, Legnaro, 7th January 28) The buncher 8.8 Mhz will generate energy dispersion what happens in RFQ1? 3 1% kevdeg/u Opt. zone 95% 9% 85% 8% 5 75% 7% % 1% 2% 3% 4% 5% 6% 7% 8% 9% 1% DeltaE/E long. emit. 36deg long. emit. 2deg long. emit. 28deg transmission The output longitudinal emittance depends on either the bunch length and the energy spread. Good transmission up to E/E = 6% 18

19 Medium Energy Beam Line transfer : MEBT Functions : - to transport the bunched beam from the exit of the 2nd RFQ to the entrance of the LINAC with appropriate transverse and longitudinal matching. - to permit fast-chopping of bunches - to stop deviated bunches. Devices needed along the MEBT: - Transverse focusing elements : 7 quadrupoles - Longitudinal focusing elements : 2 rebunchers - Deviator : 1 fast chopper - Deviated beam stop : 1 beam stop - Diagnostics, pumps 19

20 example of a completely designed MEBT : SPIRAL2 1/6 future connection Fast chopper position 7.5 kw Deviated beam stop rebuncher D-plate for RFQ beam tests and diags.tests 2

21 Beam transport with chopper off Eurisol Post-accelerator/MEBT (G. Normand, GANIL) TraceW in - CEA/ DSM/ DAPNIA/ SACM 2 X X (mm) 1-1 FM1 FM5 FM7 FM9 D14 QP1 QP2 FM12 D16 QP3 QP Fast chopper 3 Beam stop Position (m) Y Y (mm) 1-1 FM1 FM5 FM7 FM9 D14 QP1 QP2 FM12 D16 QP3 QP Position (m) W (MeV) 1-1 FM1 FM5 FM7 FM9 D14 QP1 QP2 FM12 D16 QP3 QP Position (m) T (ns) 1,5 1,5 -,5-1 -1,5 FM1 FM5 FM7 FM9 D14 QP1 QP2 FM12 D16 QP3 QP Position (m) linac 7 21

22 Beam transport with chopper on Eurisol Post-accelerator/MEBT (G. Normand, GANIL) linac 22

23 Eurisol Post-accelerator : MEBT/CHOPPER (G. Ledem, M. Di Giacomo, GANIL) Physicists requirements Chopper specifications Suppressed bunches > 9 % Max. bunches rate after chopper : 1/1 Rise/fall times : 6 ns Angle deflection : 11 mrad Max. high voltage (HV) : 2.5 kv Bunch repetition rate 1/1 1/1 1/1 1/1 Chopping pulse frequency (1/T) 8.8 MHz 88 khz 88 khz 8.8 khz N suppressed bunches 12 ns T Beam before chopper t Beam after chopper t 2 technical solutions : 23

24 Eurisol Post-accelerator : MEBT/CHOPPER (G. Ledem, M. Di Giacomo, GANIL) Solution 1 : Travelling-wave chopper Description : Association of a static B-field steerer and a 1-Ω stripline : - Beam always deflected by the B-field, - HV pulse in the stripline allows one bunch to pass Duty cycle < 1 % (instead of > 9 %!), Power consumption < 5 kw, Power losses < 6 W per plates, No pulse, no beam in the LINAC. Limitations : Coverage Factor < 75 %, Max. power dissipation per ceramic plate electrode : 6 W? Stability of the high voltage? Attenuation & overshoot of the pulse along its propagation (effects on the deflection?), Effect of the E- and B-field superposition on the beam emittance? Status : under development. 24

25 Eurisol Post-accelerator : MEBT/CHOPPER (G. Ledem, M. Di Giacomo, GANIL) Solution 2 : C-type chopper Description : Electrode divided in small plates driven by fast switchers. Limitations : Present max. power dissipation into commercial switches : around 1kW (water cooled), Effective total capacitance (plates, connections, switch) 7 pf, Many feedthroughs (vacuum?), one switch per plate Max repetition rate of switches < kv (1 MHz needed) No pulse, all the beam in the LINAC. C-types small electrodes + HV Beam E-field C-type scheme - HV Status : under study. Perspective Full beam dynamic studies, Development & test of a Travelling Wave 1-Ω stripline, Tests of pulse generators. 25

26 Eurisol Post-accelerator/MEBT (G. Normand, GANIL) Solution 1 (TW) : Emittance growth sources due to chopper E B.16 MV/m.14 T - Same integral for E and B - But frindge fields different! - (Even for central particle ) m E and B Fringe Fields 1m E Real E field (simulation) The E field can be not the same for all particles Particle distribution t F E F B q (v ^ B) = - qe, only for the central particle v 26

27 And now, the LINAC first family second family (E,B) (V,φ) Quarter Wave Resonator (QWR) Reference design : 7.8 MV/meter 27

28 Linac Design (J. Biarrotte, G. Normand ) Optimisation of linac structure using Genlin code (Saclay) 28

29 TTF = Transit Time Factor Linac Design (J. Biarrotte, G. Normand ) 29

30 Linac Design (J. Biarrotte, G. Normand ) MeV/u Sn A/Q 3

31 MEBT + LINAC Beam Dynamics TraceW in - CEA/ DSM/ DAPNIA/ SACM Linac Design (J. Biarrotte, G. Normand ) 2 1 X (mm) Position (m) Y (mm) Position (m) W (MeV) Position (m) ,5 1,5 T (ns) -,5-1 -1,5 5 1 Position (m)

32 Energy evolution Linac Design (J. Biarrotte, G. Normand ) 22 TraceWin - CEA/DSM/DAPNIA/SACM Beam Linac No Losses 2 Energy ( MeV ) Position ( m ) ,9,8,7,6,5,4,3,2,1 -,1 -,2 -,3 -,4 -,5 -,6 -,7 -,8 -,9-1 Losses ( % ) 5 1 Position ( m ) 15 TraceWin - CEA/DSM/DAPNIA/SACM 2 Normalised Emittances Norm. rms emittances ( π.mm.mrad ),13,12,11,1,9,8,7,6 TraceWin - CEA/DSM/DAPNIA/SACM Ez Ey Ex - The design is able to accept I = 1 ma (margin if prebuncher 8.8 Mhz ) - Calculations with 3D electromagnetic maps - Huge number of particles 5 1 Position ( m )

33 Steering Effect Linac Design (G. Normand ) QWR non-zero Bx(z) steering (well known) checked with analytical and real 3D (E,B) maps,4,3 Bx(z) TraceWin - CEA/DSM/DAPNIA/SACM Bz By Bx Magnetic Field Map (T),2,1 -,1 -,2 -,3 Force due to steering Steering effect before correction X Y Norm. rms emittances ( π.mm.mrad ) -,4,18,17,16,15,14,13,12,11,1,9,8,7,6,5,4,5,1,15,2 Z (m ) Emittances evolution TraceWin - CEA/DSM/DAPNIA/SACM Position ( m ) Ez Ey Ex End of the quarter-wave sections 33

34 Steering effect with steerers correction TraceWin - CEA/DSM/DAPNIA/ SACM 1 Y Y (mm) Y Y (mm) zoom Position (m) Position (m) Simulations results 4 QP49 2 Norm. rms emittances ( π.mm.mrad ),18,17,16,15,14,13,12,11,1,9,8,7,6,5,4 Emittances evolution TraceWin - CEA/DSM/DAPNIA/SACM Position ( m ) Ez Ey Ex π.mm.mrad ε x ε y ε z Entrance Exit B = Exit full Steering Steering effect can be corrected with steerers incorported to warm quads The y emittance growth is ~ 2 %. Exit steering and correction

35 Stripping studies Linac Design (G. Normand ) Stripping by using thin foil of carbon generates: - a lower intensity (about 4% of nominal one) - a bigger emittance - safety issues. - positive point: better acceleration for the same LINAC or a shorter LINAC length for the same energy QWR.65 QWR.14 HWR.27 SPOKE.385 Section1 Section 2 Section 3 Section 4 N q =1 Stripper 1 and matching section N q ~1 1< N q <~4 if multicharge beam transport - Length reduction with 2 stripper stations : 26m = 158m - Length reduction with 1 stripper station : 26m = 156m - For 132Sn: stripper <Q>= 47, Q Dispersion= σ = 1 - Fluctuation of foil thickness (Ostroumov et al. Phys.Rev.STAB vol (24)) 35

36 Stripping option : Emittance growth (Preliminary) Transverse impact Longitudinal impact 4 35 Estimated ε T growth zone,14,12 Estimated ε L growth zone X and Y in m m (2,82rm s) Energy rms (+-%),1,8,6,4,2 Limit Emittance growth % 1 % Emittance growth Emittance growth due stripping seems not to be a problem Decision : - LINAC 15 MeV/A for SN optional stripper for heavier masses. 36

37 Buncher 8.8MHz RFQ Qpoles+rebuncher Schematic view of the 2 options post-accelerator ~ 9 m 1.75 m.75 m.9 m.4 m 1.2 m Cu or Nb Cu + Fe + He Cu +Fe Cu + Fe + He Chopper Qpoles Beam dump Qpoles+rebuncher 3 % /m % /m or 1 % /m.5 MeV/u.585 MeV/u 2 %.585 MeV/u Slits : Cu + W Copper, aluminum, carbon, beryllium, tungsten SAFETY ASPECTS Without stripper 44 m 29 m LINAC.585 MeV/u 15 MeV/u 21.3 MeV/u Nb + Fe or Al + Cu + He (see layout in last for cavities and magnets) /m Exit 5-2 MeV/u Experimental area and Beam dump Experimental areas and beam dump With stripper Nb+Fe or Al+Cu+He LINAC /m 1 m Stripper 6 % in the first 5 m 12 m LINAC /m.585 MeV/u 15 MeV/u 21.3 MeV/u Nucleus reference : 132 Sn m Cu + Fe + slits (2mm W, 1cm Cu) Foil : C 3 mg/cm² Nb+Fe or Al+Cu+He Exit 5-2 MeV/u Experimental area and Beam dump Experimental areas and beam dump 37

38 Conclusions 1- Beam dynamics of the LINAC is studied. Good matching between MEBT and LINAC has been obtained 2- Steering effect not negligible, but can be corrected (as for SPIRAL 2) 3- Physics requirements reachable. (remark: for low energy output (5 MeV) E/E = ±.2% (instead of ±.1%) 4- Stripping option investigated, partial conclusions are : - One stripper at around 21.3 MeV/u OK, - Length of the LINAC is 25 % smaller than without stripper - But 6% decrease intensity (one charge kept, multicharge not obvious) - Best solution : keep 132 Sn 25+ at 15 Mev/A without stripper 5- Collaboration well started with the safety group, some results are available 38

39 and perspectives 6 - LEBT : We have to choose between the 3 hypothesis 7 - RFQs : Comparison between NC-NC and NC-SC RFQs Optimization of the matching section between RFQs 8 - MEBT : Study rebunchers in more detail Choice of chopper type 9 - LINAC : Study section for intermediate energy output and stripper 1 - END TO END : Errors studies (dynamic and static) and refine safety 39

40 Thank you! (Grazie!) 4