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RHIC upgrade plans

This article discusses the upgrade plans for the Relativistic Heavy Ion Collider (RHIC), including the implementation of stochastic cooling and the use of an IBS suppression lattice. Other upgrades mentioned are reduced beta*, 56 MHz EBIS scrubbing, transverse damper, low energy cooling, and longitudinal stochastic cooling. The article also explores the evolution of a 5-hour RHIC store with 1E9 Au/bunch and the topological features of a 56 MHz superconducting RF cavity. The potential use of an electron lens and coherent electron cooling for cooling protons is also discussed.

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RHIC upgrade plans

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  1. RHIC upgrade plans Au-Au upgrades: Stochastic cooling IBS suppression lattice Reduced * 56 MHz EBIS Scrubbing and Transverse damper Low energy cooling p↑-p↑: Reduced * 9 MHz cavity (56 MHz cavity) Nonlinear chromaticity Near integer working point (10 Hz) Electron lens

  2. LongitudinalStochastic Cooling Evolution of a 5 hour RHIC store with 1.E9 Au/bunch. Top, wall current monitor profiles taken one hour apart without cooling. IBS causes significant loss from the RF bucket. Bottom, cooling on. Beam loss is consistent with burn off in the interaction regions.

  3. Simulation is close enough to trust for design. Data Simulation

  4. Longitudinal and vertical systems in both rings mm

  5. IBS Suppression Lattice (Litvinenko… Increased phase advance per cell in the arcs. Increase transverse spring constant. Reduce closed orbit dependence on energy. Worked out quite well.

  6. Reduced * (Ions and p↑) (Tepikian, Pilat, Trbojevic… Beam in a drift travels in straight lines. Tight focus implies large size in triplet quads. Large beam size increases Susceptibility to lattice Imperfections

  7. 56 MHz superconducting rf cavity (ions and p↑) Topologically like a piece of coax shorted on one end and open on the other. Courtesy Ilan Ben-Zvi

  8. 56 MHz continued Beam current drives the cavity. Voltage controlled via cavity resonance frequency. These are standard fair in light sources. RHIC doesn’t have appreciable radiation damping. We are designing a feedback loop to make up the difference. Current plan is to use one cavity in a common pipe to longitudinally focus both beams.

  9. EBIS (Alessi, Beebe, Pikin, Okamura, … Electron beam ion source. Not limited to starting with negative ions like the tandem. Alessi et al

  10. What we can expect

  11. Scrubbing and transverse damper (Brennan, Fischer,Iriso,Zhang Electron clouds cause pressure rises and uncontrolled forces Scrubbing reduces pressure rise by removing adsorbed gas. Reducing secondary yield requires 0.1C/cm2 at keV energies

  12. Transverse Damper Pickup beam signal and feed back. 10 ms rise time. Estimate 0.1-3 GHz frequency range 12 ns variation in revolution frequency between transition and flattop. 1/GHz = ns so a trombone is needed for damping over a range in energies. Broad band (stripline?) kicker. One can imagine doubling the charge through transition. Number of bunches versus charge per bunch?

  13. Low Energy Run (Satogata, Fedotov, Pozdeyev,… Intrabeam scattering rates are very fast u is proportional to  for fixed beam size. Electron cooling adds a cold species to collide with. Fermilab cooler runs at =8.4. Lower is easier The RHIC magnets were built for high fields.

  14. Polarized Protons 9 MHz cavity

  15. Why do it? Matching stable spin direction from AGS to RHIC best at G=45.5, =25.4 is close to transition 22.5

  16. Nonlinear Chromaticity (Luo, Tepikian, Ptitsyn,Malitsky Individual particles see the other beam each turn Optimizing the lattice to get rid of momentum dependence allows for a larger beam-beam term Correction algorithm uses sextupole families Relative correction of chromaticity to nonlinear chromaticity is different for the families, allowing both to be cancelled.

  17. Near Integer (Montag… Resonances occur at Non-negative n,m lead to growth clearest space is near the integer Beam-beam spread can be largest. However, periodic drive for Q near an integer gives large closed orbit. “10 Hz” triplet vibrations yield orbit oscillations

  18. Electron Lens (Fischer, Luo, Abreu,Montag, Robert-Demolaize, Beebe, Okamura, Pikin

  19. Longer term • Coherent electron cooling (Litvinenko, Wang … Basic idea is similar to stochastic cooling. A pickup signal is amplified and applied as a kick. The pickup is an electron beam imprinted with the Debye spheres of the proton beam. The amplifier is a longitudinal instability (FEL) The kicker is the Coulomb interaction between the amplified electron beam and the ion beam. Huge effective bandwidth looks possible. We can probably cool protons with this. Significant R&D effort is underway Demonstration experiment at 40 GeV/nucleon being considered.

  20. One page treatment of stochastic cooling theory

  21. Equivalent Fokker-Planck approach is several pages.

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