The Accumulator/Pre-Booster

1. The Accumulator/Pre-Booster Bela Erdelyi Department of Physics, Northern Illinois University, and Physics Division, Argonne National Laboratory

2. Joint Work with Shashikant Manikonda (ANL) Peter Ostroumov (ANL) Sumana Abeyratne (NIU student) With assistance from JLab staff (Y. Derbenev, Y. Zhang, G. Krafft, etc.) Acknowledgements

3. ELIC Conceptual Layout • Three compact rings: • 3 to 11 GeV electron • Up to 12 GeV/c proton (warm) • Up to 60 GeV/c proton (cold)

4. Purpose: Inject from linac Accumulate ions Accelerate them Extract and send to large booster Concepts: Figure-8 shape for ease of spin transport, manipulation and preservation Modular design, with (quasi)independent module design optimization FODO arcs for simplicity and ease of implementation of optics correction schemes No dispersion suppressors Matched injection insertion Triplet straights for long dispersion-less drifts and round beam Matching/tuning modules in between Accumulator/Pre-Booster Concept

5. Figure-8 shaped; circumference 200-300 m Maximum bending field: 1.5 T Maximum quadrupole gradient: 20 T/m Momentum compaction smaller than 1/25 Maximum beta functions less than 35 m Maximum full beam size less than 2.5 cm, and 1 cm vertically in dipoles 5m m long dispersion-less sections for RF cavities, electron cooling, collimation, extraction, and possibly decoupling Sizable (normalized) dispersion for/at injection Working point chosen such that tune footprint does not cross low order resonances (tunability) Constraints

6. Protons (and possibly light ions) Stripping injection Heavy ions Repeated multi-turn injection Transverse (horizontal and possibly also vertical) and longitudinal painting Electron cooling for stacking/accumulation Injection

7. Heavy-Ion Injection and Accumulation

8. Electron Cooling

9. Intensities needed to achieve design luminosity, with some safety factors included for possible losses during Stripping Capturing, re-capturing Transfers Proton current: ~ 1A (6x1012 total particles in the ring) Heavy-ion current: ~0.5 A (1x1011 total particles in the ring) => ~10 linac pulses of ~ 250 μs length (subject to optimization) Accumulated Beam

10. h=1 RF swing necessary is [0.4,2] MHz 4 kV per cavity 50kV/turn => 12-13 cavities Synchronous phase ~ -30˚ 65000 turns for 200MeV -> 3 GeV ~100 ms acceleration time Allows acceleration with h=2 with the same cavities, if needed Acceleration

11. Finemet cavities 0.5 m long 4kV/cavity [0.35,5] MHz frequency swing Practically no maintenance needed LEIR-Type Cavities

12. Conventional single-turn fast extraction To minimize heavy-ion loss, strip once in linac and once after the pre-booster to maximize fully stripped fraction Advantages: Less beam-loss to reach fully stripped state Less severe space charge in pre-booster Drawback: lose some energy gain Extraction and stripping

13. Layout To Large Booster ARC 1 Collimation Electron Cooling Extraction Non dispersive section 1 Injection Insertion section ARC 3 Non dispersive section 2 ARC 2 RF Cavities Beam from LINAC Solenoids for Electron Cooling and Decoupling

14. Circumference Total length of the long drifts in the straights = 20m

15. Linear Optics Arc 2 Arc 1 Straight 2 Arc 3 Injection Straight 1

16. Optical modules ARC3 FODO ARC1&2 FODO INJECTION INSERT STRAIGHT TRIPLET

17. Matching/Tuning modules

18. Tunability

19. Main Parameters

20. Magnets 20

21. Beam Parameters at the End of the Pre-Booster Cycle

22. Assuming 1x1011 lead ions need to be accumulated One 250 μs long linac pulse (subject to optimization) delivers ~ 0.5 mA Assume ~50% injection efficiency (CERN experience) => 9 linac pulses Cooling time estimated to be ~130ms => Total time = 9x 250 μs (injection) + 9x130 ms (cooling) + 2x100 ms (acceleration and de-ramping) ≈ 1.4 s Assuming factor of 4 ratio between circumferences between pre-booster and large booster, and acceleration with -30˚ => 16 cycling times needed to fill the large booster => 22s (~3s for p) Large booster starts with coasting beam Pre-Booster Cycle Time

23. Design of the accumulator/pre-booster is well underway Satisfies the constraints while providing superior performance Fine tuning first order optics Space charge simulations; limits on current and emittance Spin tracking, polarization preservation studies Dynamic aperture estimation Summary and Work in Progress

24. BACKUP SLIDES

25. Assuming: 3 m long cooling section 300 mA electron current 2.5 cm beam radius ± 5 mrad beam divergence ±0.004 momentum dispersion Cooling for 3 time constants Transverse cooling time: ~ 130 ms Longitudinal cooling time: ~ 67 ms Cooling electron energies: @ injection: { 0.55394 MeV, γ=2.0840 } @ extraction: { 1.15511 MeV, γ=3.2605 } Cooling times

26. @ injection Q (0) Q (1) Q (2) Q (3) Q (4) 0 4% 70% 22% 3% @ extraction Q (0) Q (1) 80% 20% Lead Charge Distributions

27. Shorter Version (C=250m)

28. Linear Optics

29. Optical Modules

30. Main Parameters

31. Magnets

32. Laslett Tune Shift (protons) Beta=0.57 Gamma=1.21 Nt(total)=5.36E+12 rc = 1.53E-18m EN(normalized)=Beta*Gamma*9E-6 m.rad BF=1 (Peak to average current radio) laslett_tune_shift=-(Nt*rc*Bf)/(4*pi*EN*beta*gamma^2) laslett_tune_shift=-0.071.

33. Laslett Tune Shift (Lead) Beta=0.37 Gamma=1.08 Nt(total)=4.33E+10 rc = 1.53E-18m EN(normalized)=Beta*Gamma*17.5E-6 m.rad BF=1 (Peak to average current radio) laslett_tune_shift=-(Nt*rc*Bf*Q^2)/(4*pi*EN*M*beta*gamma^2)* laslett_tune_shift=-0.015.