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LHeC Recirculator with Energy Recovery – Beam Optics Choices

LHeC Recirculator with Energy Recovery – Beam Optics Choices. Alex Bogacz in collaboration with. Frank Zimmermann and Daniel Schulte. Energy Recovery Recirculating Linacs - Motivation.

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LHeC Recirculator with Energy Recovery – Beam Optics Choices

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  1. LHeC Recirculator with Energy Recovery – Beam Optics Choices • Alex Bogacz • in collaboration with Frank Zimmermann and Daniel Schulte Accelerator Seminar, CERN, Oct. 7, 2010

  2. Energy Recovery Recirculating Linacs - Motivation • Future high energy (multi-GeV), high current (hundreds of milli-Amperes) beams would require gigaWatt-class RF systems in conventional linacs - a prohibitively expensive proposition. However, invoking energy recovery alleviates extreme RF power demands; required RF power becomes nearly independent of beam current, which improves linac efficiency and increases cost effectiveness. • Energy recovering linacs promise efficiencies of storage rings, while maintaining beam quality of linacs: superior emittance and energy spread and short bunches (sub-pico sec.). • RLAs that use superconducting RF structures can provide exceptionally fast and economical acceleration to the extent that the focusing range of the RLA quadrupoles allows each particle to pass several times through each high-gradient cavity. • GeV scale energy recovery demonstration with high ratio of accelerated-to-recovered energies (50:1) was carried out on the CEBAF RLA (2003) Accelerator Seminar, CERN, Oct. 7, 2010

  3. Overview - Design Choices • Recirculating Linear Accelerator (RLA) configurations • p-60, p-140 (100), erl • Existing ER RLA’s (Jlab’s FEL & CEBAF ER Exp) • Multi-pass linac Optics in ER mode • Choice of linac Optics - 1300 FODO (1300vs1500) • Choice of quad gradient profile in the linacs (wake-field effects) • Linear lattice: 3-pass ‘up’ + 3-pass ‘down’ • Arc-to-Linac Synchronization - Momentum compaction • Quasi-isochronous lattices • Choice of Arc Optics -1350FODO vsFMC (Flexible Momentum Compaction ) • Arc Optics Choice - Emittance preserving lattices • Various flavors of FMC lattices in the second stability region (Im. gt, DBA, TEM) • Emittance dilution & momentum spread due to quantum excitations • Magnet apertures Accelerator Seminar, CERN, Oct. 7, 2010

  4. RLA Configurations . Accelerator Seminar, CERN, Oct. 7, 2010

  5. LHeC Recirculator with ER Linac 1 0.5 GeV 10 GeV/pass Arc1, 3, 5 Arc 2, 4 Arc 6 Linac 2 10 GeV/pass IP 60.5 GeV LHC Accelerator Seminar, CERN, Oct. 7, 2010

  6. CEBAF - ER Experiment (2003) Modifications include the installation of: lRF/2 path length delay chicane Dump and beamline with diagnostics Accelerator Seminar, CERN, Oct. 7, 2010

  7. Inject 55 MeV 555 MeV 1055 MeV 555 MeV Dump 555 MeV 55 MeV lRF/2 phase delay 1055 MeV 555 MeV “1 pass-up / 1 pass-down” Operation North Linac South Linac Accelerator Seminar, CERN, Oct. 7, 2010

  8. Phase-space degradation? • In an effort to gain a quantitative understanding of the 6D phase space, the following measurements were taken: • Measuring the transverse emittance of the beam in the injector, in each Arc and immediately before being sent to the dump • To characterize the longitudinal phase space, the momentum spread was measured in each Arc • Measure energy recovered beam profiles with a large dynamic range as a way to quantify beam loss and the effect of energy recovery on beam preservation • Measured the RF’s response to energy recovery Accelerator Seminar, CERN, Oct. 7, 2010

  9. ~ 1 GeV Accelerating beam 500 400 300 Arbitrary Units 200 100 0 0 5 10 15 20 25 30 35 ~ 55 MeV Decelerating beam Distance (mm) Transverse beam profiles Beam viewer near the exit of the South Linac 3-wire scanner x 2 beams = 6 peaks Accelerator Seminar, CERN, Oct. 7, 2010

  10. Beam Profiles of ER Beam • Beam profiles (55 MeV, 1mA beam) measured with a wire scanner and 3 downstream PMTs • Each profile (X and Y) is fit with a function of the form: • F = Gaussian(Core) + Gaussian(“Halo”) + Background • Quantify beam loss by: • Ratio for X-profile is 1x10-4 • Beam loss for Y-profile is below the noise level 5 orders of dynamic range Y-profile X-profile (courtesy A. Freyberger) Accelerator Seminar, CERN, Oct. 7, 2010

  11. Gradient modulator drive signals with and without energy recovery in response to 250 sec beam pulse entering the RF cavity (SL20 Cavity 8) RF Response to Energy Recovery 250 ms without ER with ER Accelerator Seminar, CERN, Oct. 7, 2010

  12. JLAMP 2-pass FEL with ER Accelerator Seminar, CERN, Oct. 7, 2010

  13. LHeC Recirculator with ER Linac 1 0.5 GeV 10 GeV/pass Arc1, 3, 5 Arc 2, 4 Arc 6 Linac 2 10 GeV/pass IP 60.5 GeV LHC Accelerator Seminar, CERN, Oct. 7, 2010

  14. 5 150 0.5 BETA_X&Y[m] PHASE_X&Y DISP_X&Y[m] 0 0 0 0 BETA_X BETA_Y DISP_X DISP_Y 56 0 Q_X Q_Y 56 Linac Optics - 1300 FODO Cell E = 0.5 GeV phase adv/cell: Dfx,y= 1300 2×9 cavities 2×9 cavities 700 MHz RF: Lc =100 cm 5-cell cavity Grad = 17.361 MeV/m DE= 555.56 MV linac quadrupoles Lq=100 cm GF= 0.103 Tesla/m GD= -0.161 Tesla/m Accelerator Seminar, CERN, Oct. 7, 2010

  15. 5 200 BETA_X&Y[m] DISP_X&Y[m] 0 0 0 BETA_X BETA_Y DISP_X DISP_Y 1008 Linac 1 - Focusing profile E = 0.5 - 10.5 GeV quad gradient 18 FODO cells (18 ×18 = 324 RF cavities) Accelerator Seminar, CERN, Oct. 7, 2010

  16. 5 500 BETA_X&Y[m] DISP_X&Y[m] 0 0 0 BETA_X BETA_Y DISP_X DISP_Y 1008 0.5 PHASE_X&Y 0 0 Q_X Q_Y 1008 Linac 3 (Linac 1, pass 2) - Optics E = 20.5 - 30.5 GeV betatron phase advance Accelerator Seminar, CERN, Oct. 7, 2010

  17. 800 800 0.5 0.5 BETA_X&Y[m] BETA_X&Y[m] DISP_X&Y[m] DISP_X&Y[m] -0.5 -0.5 0 0 0 BETA_X BETA_Y DISP_X DISP_Y 1008 0 BETA_X BETA_Y DISP_X DISP_Y 1008 800 0.5 800 0.5 BETA_X&Y[m] DISP_X&Y[m] BETA_X&Y[m] DISP_X&Y[m] -0.5 -0.5 0 0 0 BETA_X BETA_Y DISP_X DISP_Y 1008 0 BETA_X BETA_Y DISP_X DISP_Y 1008 800 0.5 800 0.5 BETA_X&Y[m] BETA_X&Y[m] DISP_X&Y[m] DISP_X&Y[m] -0.5 -0.5 0 0 0 BETA_X BETA_Y DISP_X DISP_Y 1008 0 BETA_X BETA_Y DISP_X DISP_Y 1008 Linac 1 - multi-pass + ER Optics 50.5 GeV 10.5 GeV 0.5 GeV 60.5 GeV 30.5 GeV 40.5 GeV 20.5 GeV 30.5 GeV 40.5 GeV 10.5 GeV 50.5 GeV 20.5 GeV Accelerator Seminar, CERN, Oct. 7, 2010

  18. 5 200 BETA_X&Y[m] DISP_X&Y[m] 0 0 0 BETA_X BETA_Y DISP_X DISP_Y 1008 Linac 2 - Focusing profile E = 10.5 - 0.5 GeV (ER) quad gradient 18 FODO cells Linac 2 multi-pass optics with ER - mirror symmetric to Linac 1 (see previous slide) Accelerator Seminar, CERN, Oct. 7, 2010

  19. Arc Optics - 1350 FODO Cell 50.5 GeV phase adv/cell: Dfx,y= 1350 Arc dipoles: $Lb=400 cm $B=2.2 kGauss $ang=0.3 deg. $rho = 764 meter Arc quadrupoles $Lq=100 cm $G= 1.2kG/cm Accelerator Seminar, CERN, Oct. 7, 2010

  20. 1350 FODO Cell Emittance dispersion 〈H〉 averaged over bends Momentum compaction Accelerator Seminar, CERN, Oct. 7, 2010

  21. Emittance growth due to quantum excitations Accelerator Seminar, CERN, Oct. 7, 2010

  22. Momentum spread due to quantum excitations Accelerator Seminar, CERN, Oct. 7, 2010

  23. Quasi-isochronous condition – Arc into Linac Momentum compaction Accelerator Seminar, CERN, Oct. 7, 2010

  24. Quasi-isochronous FMC Cell Emittance dispersion 〈H〉avereged over bends Momentum compaction factor of 2.5 smaller than FODO factor of 27 smaller than FODO Accelerator Seminar, CERN, Oct. 7, 2010

  25. Arc Optics – 1350 FODO vs FMC Cell FMC Cell 1350 FODO Accelerator Seminar, CERN, Oct. 7, 2010

  26. Quasi-isochronous condition – Arc into Linac Momentum compaction factor of 27 smaller than FODO Accelerator Seminar, CERN, Oct. 7, 2010

  27. FMC ‘Imaginary gt’ Cell 50.5 GeV second stability region: Dfx,y > 1800 Arc quadrupoles $G0= -1.53kG/cm $G1= 5.06kG/cm $G2= -5.32 kG/cm $G3= 5.07 kG/cm Arc dipoles: $Lb=400 cm $B=2.2 kGauss $ang=0.3 deg. $rho = 764 meter Accelerator Seminar, CERN, Oct. 7, 2010

  28. FMC ‘Double Bend Achromat’ Cell 50.5 GeV second stability region: Dfx > 1800 Arc quadrupoles $G0= 2.05 kG/cm $G1= 2.90kG/cm $G2= -4.07 kG/cm $G3= 2.97 kG/cm Arc dipoles: $Lb=400 cm $B=2.2 kGauss $ang=0.3 deg. $rho = 764 meter Accelerator Seminar, CERN, Oct. 7, 2010

  29. FMC ‘Theoretical Emittance Minimum’ Cell 50.5 GeV second stability region: Dfx > 1800 Arc quadrupoles $G0= 2.92kG/cm $G1= 2.89kG/cm $G2= -4.08 kG/cm $G3= 2.97 kG/cm Arc dipoles: $Lb=400 cm $B=2.2 kGauss $ang=0.3 deg. $rho = 764 meter Accelerator Seminar, CERN, Oct. 7, 2010

  30. Arc Optics – Cumulative emittance growth Arc 1 , Arc2 Arc 3 Arc 4 , Arc5 Imaginary gt Optics TEM-like Optics DBA-like Optics total emittance increase (all 5 arcs): DexN = 1.25 × 4.5 mm rad =5.6 mm rad Accelerator Seminar, CERN, Oct. 7, 2010

  31. Highest Arc Optics – Emittance growth 50.5 GeV, g = 105 TEM-like Optics emittance increase (last arc): DexN = 4.5 mm rad RMS fluctuations of DE/E0 = 2.7 × 10-4 total emittance increase (all 6 arcs): DexN = 1.25 × 4.5 mm rad =5.6 mm rad Accelerator Seminar, CERN, Oct. 7, 2010

  32. Arc 5 – Beam envelopes 50.5 GeV, g = 105 exN = 50 mm rad Dp/p= 2.7 × 10-4 TEM-like Optics Accelerator Seminar, CERN, Oct. 7, 2010

  33. Arc 1 – Beam envelopes exN = 200 mm rad 10.5 GeV Dp/p= 5 × 10-4 Imaginary gt FMC Optics Accelerator Seminar, CERN, Oct. 7, 2010

  34. Conclusions • Proof-of-existence ER RLAs: Jlab FEL, CEBAF • Solution for Multi-pass linac Optics in ER mode • Choice of linac Optics - 1300 FODO • Linear lattice: 3-pass ‘up’ + 3-pass ‘down’ • Optimized quad gradient profile in the linacs (wake-field effects) • Arc-to-Linac Synchronization - Momentum compaction • Quasi-isochronous lattices • Choice of Arc Optics - Flexible Momentum Compaction • Arc Optics Choice - Emittance preserving lattices • Arcs based on variations of FMC optics (Im. gt, DBA, TEM) • Acceptable level of emittance dilution & momentum spread • Magnet apertures Accelerator Seminar, CERN, Oct. 7, 2010

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