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i ssues for e+ stacking in the rings

i ssues for e+ stacking in the rings. Frank Zimmermann IWLC2010, CICG, Geneva, 21 October 2010 thanks to Fanouria Antoniou, Eugene Bulyak, Peter Gladkikh, Yannis Papaphilippou, Louis Rinolfi, Junji Urakawa, Alessandro Variola, Alessandro Vivoli. various Compton-scheme scenarios

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i ssues for e+ stacking in the rings

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  1. issues for e+ stacking in the rings Frank Zimmermann IWLC2010, CICG, Geneva, 21 October 2010 thanks to Fanouria Antoniou, Eugene Bulyak, Peter Gladkikh, Yannis Papaphilippou, Louis Rinolfi, Junji Urakawa, Alessandro Variola, Alessandro Vivoli

  2. various Compton-scheme scenarios • Compton sources • Compton linac (“pulsed”) • Compton ring – CR (“pulsed”), or • Compton ERL – CERL (“continuous”) • accumulation rings • ILC damping ring – optimized? • CLIC pre-damping ring - optimized • two CLIC stacking rings - dedicated

  3. ILC & CLIC parameters, differences & needs

  4. Compton source basics collide 1.3-1.8 GeV e- beam with laser pulse stored in optical cavity (l~1 mm); yield ~ 0.2 g/e-for single 600 mJ cavity* (CLIC) ~1 g/e-for several optical cavities (ILC) convert Compton-scattered photons to e+/e-, and capture e+:yield ~ 0.01 e+/g * example numbers: *Tsunehiko Omori, 11 October 2008

  5. stacking approach • most laser Compton sources (R-Ring, C-ERL) do not provide required e+ intensity / pulse • e+ must be accumulated over ~50-3000 “shots” in (pre-)damping or dedicated stacking ring • longitudinal stacking: - transverse emittance fills aperture - longitudinal aperture larger than injected emittance with low-a & high RF voltage - longitudinal damping rate is ~2x faster than transverse

  6. Compton Ring Scheme for CLIC L. Rinolfi Compton Ring: E = 1.06 GeV C = 46.8 m VRF = 200 MV fRF = 2 GHz CP = 0.05 m 1100 turns makes 312 bunches with 4.4x109 e+/bunch e+ DR 2.86 GeV 2.86 GeV e+ PDR and Accumulator ring 156 ns/turn, 312 bunches with 6.2x109 e-/bunch RF gun Injector Linac 2.66 GeV Drive Linac 1 GeV 2 GHz Compton ring 2 GHz Laser pulse: E = 1.164 eV r = 0.005 mm l = 0.9 mm g/e+ Target Pre-injector Linac for e+ 200 MeV g 156 ns x1100 turns => 170 ms pulse length for both linacs  4x108 photons /turn/bunch Stacking cavity 2 GHz YAG Laser  4x106 pol. e+/turn/bunch

  7. Compton ERL Schemefor CLIC L. Rinolfi (CERN) and T. Omori (KEK) ILC-CLIC e+ studies 14-May-2009

  8. stacking scheme / simulation ingredients • stacking in longitudinal phase space RF bucket >> longitudinal edge emittance of injected e+ • ingredients: sinusoidal rf, momentum compaction, 2nd order momentum compaction, radiation damping, quantum excitation, initial e+ parameters • injection septum placed at location with large dispersion; septum blade << transverse beam size • inject every Nth turn into same (P)DR bucket (large bunch spacing for e- beam; arranged by suitable CR/CERL-PDR circumference difference, e.g. 0.15 m) • either fast septum bump/kick or static injection

  9. initial e+ parameters (A.Vivoli’s ILC simulation,’08) ERLScheme e+ e- e-,g → germs init = 72 meV-s e- g e+ I assume this longitudinal emittance Compton cavities up to 2.424 GeV Superconducting Linac with quadrupole focusing Target 1.3 to 1.8 GeV superconducting ERL Capture Section with solenoid (+ Chicane & Bunch Compressor) Up to 150 MeV Pre-Damping Ring e-injector + Bunch Compressor need similar simulation for CLIC

  10. Tb-to-b(CR)=20ns (50MHz): 1st turn of PDR stacking 20 ns (1) 1st turn begin 0.5 ns e+ bunches from ERL or CR PDR 20 ns (2) 1st turn end 0.5 ns e+ bunches from ERL or CR PDR Omori-san style plot (only rough schematic here; take ring circumference = c x 39.5 ns)

  11. Tb-to-b(CR)=20ns (50MHz): 2nd turn of PDR stacking 20 ns (1) 2nd turn begin 0.5 ns e+ bunches from ERL or CR PDR 20 ns (2) 2nd turn end 0.5 ns e+ bunches from ERL or CR PDR Omori-san style plot

  12. Tb-to-b(CR)=20ns (50MHz): 40th turn of PDR stacking 20 ns (1) 40th turn begin 0.5 ns e+ bunches from ERL or CR PDR 20 ns (2) 40th turn end 0.5 ns e+ bunches from ERL or CR PDR Omori-san style plot

  13. CLIC PDR stacking simulation, example, doff=11.5% septum at d=doff-2sd0 septum at d=doff+2sd0 septum bump 1st turn, 1 bunch 2nd turn, 1 bunch septum at d=doff+2sd0 septum at d=doff+2sd0 7th turn, 1 bunch 20th turn, 1 bunch

  14. CLIC PDR stacking simulation, example, doff=11.5% 2nd bunch septum at d=doff-2sd0 septum at d=doff+2sd0 41st turn, 2 bunches 400th turn, 10 bunches 1st bunch septum at d=doff+2sd0 septum at d=doff+2sd0 2400st turn, 60 bunches 17.3 ms after last inj.

  15. treatment of synchrotron radiation R. Siemann, HEACC 1988 model A model B

  16. simulated stacking efficiency vs. initial d offset tracking model A maximum efficiency ~86% for d~11.5%

  17. simulated stacking efficiency vs. initial d offset zoff=1 cm tracking model B model A gives about the same result as model B efficiency boosted by injection offset in d and z maximum efficiency ~84.3% for d~11.5%

  18. simulated stacking efficiency vs. a2 tracking model B

  19. Compton source megatable - 2008

  20. stacking is helped by: • short damping time • small longitudinal emittance • large ring momentum acceptance • (low a, low a2, large VRF, higher harmonic rf) • energy pre-compression • off-phase off-energy injection • long time between injections • long time for final damping

  21. longitudinal phase space of CLIC PDR optimized for stacking [F.Z. et al, PAC2009] PDR design [F. Antoniou, Y. Papaphilippou]

  22. condition for fast septum-bump scheme: DEloss(1 synchrotron period) > 4 sE0 or DEloss > 4 (sE0+E sz0 Qs/(acC)) (conservative) in our example for CLIC PDR: 328 MeV (80 turns) > 8 MeV easily fulfilled no septum bump needed if: static injection DE (1 turn) > 4 sE0

  23. conditions for static injection scheme : DEloss(1 synchrotron period) > 4 (sE0+E sz0 Qs/(acC)) [e.g. ~ 0.02 E] no septum bump needed if example for CLIC-ERL SRs: DEloss/turn =3.5MeV, sE0/E =0.0028, sz0~7 mm,Qs~0.05, dEinj/E~0.081 (!) both conditions fulfilled DEsync.osc.(1 turn) ~ 2p QsdEinj> 4 sE0

  24. CLIC ERL scheme detail 312 bunches / train 1 train / ring e+ PDR 400 m 50 Hz 0.5 ns throw away 2 bunches 312 bunches spaced by 0.5 ns => 156 ns / turn Stack in the same bucket every 63th turn Number of stacking in the same bucket: 2035 63 x 2035 = 128 205 turns (64x2003=128192) 128 205 x 156 ns = 20 ms (314 bunches, every 63th turn) SR 1 SR 2 25 Hz 47.1 m 47.1 m ERL 32 ns Updated scheme

  25. phase space of stacking ring injected bunch (±2 s)

  26. the first few turns after injection bunch #1

  27. injecting bunches # 2, 3 and 6

  28. after injecting the last bunch (# 1864)

  29. simulations summary

  30. “Face-to-face” meeting on polarized e+ source for CLIC with Urakawa san and Omori san, 8 July 2010, 14:00

  31. white board writings by Omori san

  32. face-to-face discussion with Omori san and Urakawa san - highlights: • use stacking-ring ring circumference equal to 63x5-1=314 [0.5 ns] (throwing away two bunches) instead of 64x5+1=321 (throwing away nine bunches) • use two stacking rings with alternating injections (turn by turn) to relax the damping-time requirement by a factor of 2 • electron charge in Compton ERL is a free parameter, keeping ERL beam current constant – this may be used to relax damping time! • After the meeting Junji Urakawa asked the Ukrainian collaborators Eugene Bulyak and Peter Gladkikh to design a CLIC (laser) stacking ring with the required short damping time (~100 ms). • They have made progress ever since • (several emails with Louis Rinolfi / week).

  33. conclusions fast bump and static injection schemes simulated longitudinal stacking efficiency > 95% for all cases (ILC, CLIC; C-ERL, C-Ring; (P)DR, SRs) large off-momentum dynamic aperture up to dinj~10% (!) is required - off-momentum transverse dynamic aperture !? - E pre-compression [R. Chehab] and/or fast damping (~50 ms for CLIC SRs)

  34. open questions lattice design for stacking rings (FFAG option?) wiggler or laser and RF for stacking ring stacking-optimized parameters for P(DR)s impedance & stability for 10s of MV RF? (K. Yokoya) nonlinear wigglers damping large amplitudes? laser-collision with dispersion (E. Bulyak) → “Maxwell's demon”!

  35. thank you for your attention!

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