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eRHIC Main Linac Design

eRHIC Main Linac Design. E. Pozdeyev + eRHIC team BNL. Outline and Design Parameters. e-ion detector. Possible locations for additional e-ion detectors. eRHIC. PHENIX. Main ERL (1.9 GeV). STAR. Beam dump. Low energy recirculation pass. Four recirculation passes. Electron

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eRHIC Main Linac Design

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  1. eRHIC Main Linac Design E. Pozdeyev + eRHIC team BNL

  2. Outline and Design Parameters e-ion detector Possible locations for additional e-ion detectors eRHIC PHENIX Main ERL (1.9 GeV) STAR Beam dump Low energy recirculation pass Four recirculation passes Electron source • Npass = 5 up + 5 down • dE/ds = 8 – 8.5 MeV/m • L = 230 m E. Pozdeyev, BNL

  3. Linac Design cryomodule F D F D F D F 11.9 m 1m quads • Nfc = 6 (per module) • N3h = 2 (per module) • N modules = 18 • dE/ds = 8 – 8.5 MeV/m • Ef = 19.5 MeV/m • E3h = 19.0 MeV/m • G = 340 Gauss/cm • Lq=20 cm • μ0 = 90º Cryomodule 703.75 MHz 5 cell, 1.4 m with dampers 2.1 GHz 5 cell, 0.75 m with dampers E. Pozdeyev, BNL

  4. Optical Functions and Beam Size -functions in the linac (m) 5 up + 5 down, unity recirculations (not shown) Beam size in the linac (mm) 5 passes up unity recirculations (not shown) E. Pozdeyev, BNL

  5. Multipass transverse BBU I=270 mA • Beam Breakup as a function of the HOM frequency spread • 72 modes per cavity • simulated and measured modes in copper model with HOM absorbers • 5 random seeds x 2 HOM orientations = 62 fHOM distributions • no specific optimization of beam optics to maximize BBU threshold E. Pozdeyev, BNL

  6. Energy Loss / Spreadcaused by the longitudinal wake Loss factor (no fundamental wake): k|| = 0.57 V/pC Average energy loss per e: dEloss = -12.3 MeV Full energy spread: dEspread = 21.3 MeV Monopole wake field simulated by ABCI. Fundamental wake is the convolution of the cosine wake with the charge distribution. Supposedly, the fundamental wake is recovered. E. Pozdeyev, BNL

  7. Compensation of the energy spread Energy loss (12.3 MeV) can be compensated only by off-phasing or by an additional cavity without recovery. The energy spread can be reduced if the beam phase width is increased and beam is matched to the RF wave. Smal d, Large dE For Ei = 21.3 MeV and V=100 MeV estimated f~ 38º. The initial bunch phase width for the fundamental RF is ~ 35º. Longer wavelength RF is required to reduce the energy spread. dE compensation has to be done at lower energies (~100 MeV). The low frequency RF can be used up to E ~ 100 MeV. Large d, fits the RF wave -> small dE The optimized phase width can be estimated as The energy spread compression can be estimated as E. Pozdeyev, BNL

  8. Compensation of the energy spread λ = 1.7 m (~175 MHz) V = 100 MeV m56 = -60 m566 = -235 (in RF degrees) Energy spread compressed by 5.8 times (21.3 -> 3.68 MeV) Compensated energy spread as a function of RF frequency. Note 3rd harmonic RF can increase the suppression ratio. E. Pozdeyev, BNL

  9. Minimum Turn-On time Assuming the maximum current ramp rate is limited by the available RF power Assuming V=20 MV, PRF=10 kW, Trev=13 μs, Ibeam=280 mA, nap=5 E. Pozdeyev, BNL

  10. R&D items • Strong ions beam cooling (CEC, for example) can reduce the required electron current and alleviate intensity related effects - R&D on the ion beam that can benefit e-linac design • Compact, multi-cell cryomodule without sacrificing HOM damping efficiency • Other linac optics options (smaller -function, “concentrated” 3rd harmonic in designated cryomodules, etc. ) • Increase BBU threshold • Lower frequency RF to increase the bunch length and possibly drop the 3rd harmonic E. Pozdeyev, BNL

  11. Other Linac Setup scenarios New tunnel construction can be expensive. Linac can be constructed in RHIC tunnel. 2 x 200 m SRF linac 10-12.5 MeV/m 4-5 GeV per pass 5 (6) vertically separated passes ePHENIX eSTAR E. Pozdeyev, BNL

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