1. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Last results for beam dynamics on MEBT line and superconducting LINAC Joint Meeting Orsay 7 th Patrick Bertrand Jean-Luc Biarrotte Marco Di Giacomo Gwenal Le Dem Marie-Hélène Moscatello Guillaume Normand

2. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics SUMMARY - Introduction - Chopper - MEBT beam dynamics - LINAC without stripper - LINAC with stripper - Safety - Conclusion

3. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics 3 independant post-accelerators: - very low energy (not studied here), - low energy (1–5 MeV/u ), - high energy 5 – 150 MeV/u for 132 Sn 25+. Note: Low Energy LINAC will be very similar to the first part of the high one. Aims: Accelerate all radioactive ions produced in the ISOL target. Principle: RFQ + MEBT with fast Chopper + 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 ion can be accelerated) Introduction

4. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Maximal energy 132 Sn 25+ 150 MeV/u Energy tuning step1 MeV/u Beam time structure88.05 MHz (11.4 ns) Energy definition< 0.1 % Time width per beam bunch (FWHM)0.5 ns Max. beam intensity10 12 –10 13 /s Emittance (π.mm.mrad) 1 to 2 Pulse rate10 ns – 1 ms Stripping stationNo but still an option Parameters

5. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics MEBT with chopper

6. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Chopper Chopper feature : - Main idea: use a magnetic dipolar field to deviate the beam, and add an electric field when the beam goes to the LINAC. - Length: 650 mm - Distance between the two plates: 20 mm - Voltage between plates: 3000 V Note that this is only one of the solutions which can be studied. Alternative solution could be two choppers for example. 20 mm 650 mm

7. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Bunch repetition rate1/101/1001/10001/10000 Chopping pulse frequency (1/T)8.8 MHz880 kHz88 kHz8.8 kHz Beam before chopper 12 ns Beam after chopper t t T N suppressed bunches Physicists requirements Chopper specifications Suppressed bunches > 90 % Max. bunches rate after chopper : 1/10 Rise/fall times : 6 ns Angle deflection : 11 mrad Max. high voltage (HV) : 2.5 kV Courtesy by G. LE DEM 2 technical solutions Chopper

8. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Solution I : Travelling wave chopper Description :  Association of a static B-field steerer and a 100-Ω stripline : - Beam always deflected by the B-field, - HV pulse in the stripline allows one bunch to pass  Duty cycle 90 % !),  Power consumption < 5 kW,  Power losses < 400 W per plates,  No pulse, no beam in the LINAC. Limitations :  Coverage Factor < 75 %,  Present max. power dissipation per ceramic plate electrode : 100 W (SPL),  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. Travelling-wave chopper Courtesy by G. LE DEM

9. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics E-field Beam C-types small electrodes + HV - HV C-type scheme Solution II : C-type chopper 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) ≈ 70 pF,  Many feedthroughs (vacuum ?), one switch per plate  Max repetition rate of switches < 1 MHz @ 2.5 kV (10 MHz needed)  No pulse, all the beam in the LINAC. Status : under study. Perspective  Development & test of a Travelling Wave 100-Ω stripline,  Tests of pulse generators. C-type chopper Courtesy by G. LE DEM

10. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics 0m1m EBEB 0.14 T 0.16 MV/m Air gap 110 mm Hard Edge Magnetic Lenght 650 mm Intégral field 100 Gm Type steerer window-frame Courant I = 10 A Thanks to M. Duval Chopper : 3 D fields Dipole E + B

11. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Qpole – Qpole – Qpole – Buncher – Chopper – Qpole – Qpole – Beam dump – Buncher – Qpole – Qpole MEBT Chopper OFF

12. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics MEBT Chopper ON

13. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Deflection angle : 11 mrad Maximum power in beam dump : <123 W for 132 Sn MEBT Chopper ON

14. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Emittance growth sources Fringe Field E Particle distribution t q (v ^ B) = - qE only for the central particle FEFE FBFB The E field could be not the same for all particles v It’s possible to create the same integral for E and B field, but it’s impossible to have the same E and B during the all path, even for the central particle. 0m 1m EBEB 0.14 T 0.16 MV/m Real E field (simulation)

15. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Voltage + 10% to test which level of repeatability must be reach. Beam dynamics with voltage fluctuation

16. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics - We have simulated the MEBT with 3D field maps for E and B. - Even if the shapes of the two fields are different, the beam dynamics, after some changes of the line, shows results very close to those we have obtained with perfect field. - Losses are 0% when the chopper is ON and 100% when it is OFF. - Simulations with 1 to 10 % of variation in the E field value show that 1 or 2 % is acceptable (and feasible according to chopper team), and even with 10 %, the beam arrives at the end of the LINAC without losses. MEBT Beam dynamics conclusion

17. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics LINAC

18. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Simulations have shown that space charge effect is negligible. Nevertheless the design chosen is able to accept I = 1 mA. A low-energy machine has been designed for 0.95 MeV/u < E < 5.0 MeV/u for a length of 23.8 m. Particles at the exit of RFQ have been used as entrance data set. TTF LINAC Section 1Section 2Section 3Section 4Total Cavity Freq. (MHz)88.05 176.1264.15 Cavity β0.0650.140.270.385 n° Cav/cryomodule1 QWR3 QWR8 HWR14 SPOKE Total n° Cavities152780154276 Length17.926.159.0103.8206.8 Output energy-2.1 -19.99.3-62.520-150.0

19. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics LINAC + MEBT Beam Dynamics

20. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics LINAC Beam Dynamics Emittances Energy Losses Synchronous Phase

21. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Input energy585.4 keV/u (β = 0.035 150 MeV/u Tranverse Input norm. RMS emittance 0.12 π.mm.mmrad Longitudinal Input norm. RMS emittance 0.1 π.mm.mmrad Accelerating gradient operation point 7.8 MV/m Input parametersOutput parameters Parameters

22. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Steering Effect Beam without steering Force due to steering Steering effect before correction Simulation gives a y shift < - 0.65 mm in the worst case. End of the quarter-wave sections The amplitude of the steering due to the non-zero Bx(z) component of the magnetic field in the case of quarter-wave resonator must be checked.3D E and B have been used.

23. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Steering effect with steerers correction Simulations results Calculations and simulations show that steering effect has a major impact but can be corrected with steerers: The y emittance growth is ~ 20 %. Y shift after correction with steerers: 0 mm

24. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Stripping option Section1Section 2Section 3Section 4 QWR 0.065 QWR 0.14 HWR 0.27 SPOKE 0.385 Stripper 1 and matching section N q =1 1< N q <~4 if multicharge beam transport Stripping, using thin foil of matter to growth the ion charge, generates a lower intensity, a bigger emittance of the beam and safety problems. The positive point: a better acceleration for the same length of LINAC or a shorter length for the same energy. N q ~10 A first estimation indicates that the length of the LINAC with two strippers (end of section 1 and end of section 2) could be reduced from 206m to 138m (-33%). But the strippers stations including elements before and after each foil for the dynamics purpose enhance the length, and the cost obviously. Actually, simulation shows that it is better to use only one stripper at the end of section 2 (~156 m all inclusive) for similar performances.

25. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Stripping option Before stripperAfter stripper (with Energy shift only)

26. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics For 132 Sn: stripper = 47 Q Dispersion : σ = 1 Charge equilibrium thickness Charge distribution Multicharge transport Efficiency Efficiency with two strippers : ~15%, 40% with one stripper Second stripper (21.3 MeV/u): 3 mg/cm² (Carbon) Stripping option Straggling To take into account the incertitude on foil thickness, 10% fluctuation have been introduced (pessimistic). (See also Ostroumov et al. Phys.Rev.STAB vol.7 090101 (2004) ) Stripper1 (21.3 MeV/u) ΔE shift (MeV/u)-0.96 E rms (MeV/u)0.040 E FWHM (MeV/u)0.101 (mrad)0.45 Angle rms (mrad)0.31 Angle FWHM (mrad)0.49

27. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Emittance +100% : ε x = 0,250 ε y = 0,234 ε L = 0,2 Emittance +500% : ε x = 0,75 ε y = 0,702 ε L = 0,6 Stripping : emittance growth

28. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Limit Emittance growth (Preliminary results) In summary, the emittance growth due to the stripping, in longitudinal and transversal, seems to not be a problem to achieve the EURISOL goals. Transverse impactLongitudinal impact Estimated ε T growth zone Estimated ε L growth zone 70 100

29. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics LINAC conclusions - The beam dynamics of the LINAC has been studied. A good matching between MEBT and LINAC has been obtained - The steering effect is not negligible but can be corrected The goals for the parameters are reachable (n ote that for low energy output (5 MeV) ΔE/E=±0.2% (0.1 required)), but we need an output at the end of the second section to provide beam between 5 and 20 MeV. - The stripping option is investigated, partials conclusions are : - One stripper at around 21.3 MeV/u (rather than two at 4.3 and 21 MeV) which is by chance the end of the second section - The length of the LINAC is 25 % litter than without stripper - Intensity will decrease of 60% if we transport only one charge (and feasibility of multicharge transport is not obvious) - The beam can’t be perfectly clean - The emittance growth seems to not be a problem due to the large acceptance of the LINAC and the ΔE/E at the end is still in the requirement. - A collaboration has started with the safety group, some results are already available

30. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics RFQ Qpoles+rebuncher LINAC Chopper Qpoles Beam dump Qpoles+rebuncher LINAC With stripper LINAC Without stripper 0.585 MeV/u150 MeV/u Exit 5 - 20 MeV/u Experimental area and Beam dump 209 m 44 m 102 m 10 m Stripper 0.585 MeV/u150 MeV/u 21.3 MeV/u 0.585 MeV/u Safety and options 0.005 MeV/u 30 % 10 -5 - 10 -4 /m 0 or 100 % 2 % ~ 9 m1.75 m0.75 m0.9 m 0.4 m 1.2 m 0 % 60 % in the first 5 m Cu or NbCu + Fe + HeCu +FeCu + Fe + He Nb + Fe or Al + Cu + He (see layout in last email for cavities and magnets) Nb+Fe or Al+Cu+He Slits : Cu + W Foil : C 3 mg/cm² Cu + Fe + slits (2mm W, 1cm Cu) Copper, aluminum, carbon, beryllium, tungsten Experimental areas and beam dump Experimental areas and beam dump Exit 5 - 20 MeV/u Experimental area and Beam dump 12 or 3 Buncher 8.8MHz 1 2 3 10 -5 - 10 -4 /m Nb+Fe or Al+Cu+He In red : losses in pps In blue : matter 44 m 21.3 MeV/u Nucleus reference : 132 Sn 25+

31. Orsay January 2008 ‹#› Post-accelerator Beam Dynamics Few next steps : - Finish the stripping option study (cost, safety…) - Check the beam dynamics of the MEBT in more details - Make measurements with a prototype of meander line to see the deformation of the field shape - Start an error study for the MEBT + LINAC beam dynamics -… … to be continued