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Recirculating pass optics

This study focuses on optimizing the optics design for recirculating passes in the eRHIC accelerator, enhancing control over beam parameters and minimizing dispersion at the interaction point. The development includes modifications from FODO cell to FMC-cell-based optics, enabling an isochronous lattice. Ongoing work involves finalizing the interaction region straight design and conducting tracking studies to assess tolerances in magnet errors and misalignments.

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Recirculating pass optics

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  1. Recirculating pass optics V.Ptitsyn, D.Trbojevic, N.Tsoupas

  2. 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 Recirculation passes in eRHIC design At present design of eRHIC the beam passes the main linac five times during acceleration. Four of the beam recirculation passes will be placed in the tunnel. Lower energy pass can be put locally. Possible location of the recirculation passes in the tunnel

  3. The RHIC tunnel curvature defines average orbit radius for the passes. The dipole magnet strength is limited by synchrotron radiation loss power. Beam power loss due to synchrotron radiation for 0.26 A beam at 10 GeV versus dipole filling factor.

  4. Longitudinal transport For acceleration on the crest the recirculating passes should be isochronous enough in order to have acceptable momentum spread after deceleration dp/p, 1e-3 dp/p, 1e-3 z, mm z, mm R56=500 mm R56=20 mm 3rd harmonic cavities are used in both main and pre-accelerator linacs

  5. Basic cell for the recirculating passes 81 m FMC cell (D.Trbojevic) Dipole filling factor: 54% Reduced length Tuned to ~0 momentum compaction For 10GeV: Largest gradient: 7.7 T/m Dipole field: 1.6 kGs Dipole length: 5.5 m Quad length: 0.6 m

  6. Summary of synchrotron radiation

  7. Tunable R56 parameter R56 versus gradient of QD2 quad (central quad) Should give at least +-0.3m tuning range for R56 on the whole pass. Beta_max change within 15%. For this basic cell there are also some other ways to tune R56.

  8. Basic cell: beta-functions Phase advances: m_x = 1.6p m_y = 1.4p

  9. Arc lattice 4 basic FMC cells + matching sections The whole arc transfer is achromatic. R56=0 and adjustable.

  10. One sextant Arc+ straights with no IR • Separated functions: • R56 tuning: arcs • Phase trombone: straights • Path length tuning: in • area of IR insertion (IR12)

  11. Achromatic Spreader N.Tsoupas

  12. Beam parameters and dispersion for each line of the separator

  13. Interaction Straight Layout H-plane V-plane Presently considered geometry of the interaction region straight. Ongoing work on the optics to minimize (or eliminate) dispersion at the IP.

  14. Summary • Optics of recirculation passes has been modified, from FODO cell to FMC-cell based optics. Isochronous lattice. Provides the flexible control of R56 parameter. • Initial separator/merger design has been developed. • Ongoing work: • Finalizing interaction region straight design. • Tracking with magnet errors/misalignments to study tolerances.

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