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Hadron beam intensity limits

Wolfram Fischer Thanks to: M. Blaskiewicz, A. Fedotov, C. Montag, L. Merminga, V. Ptitsyn eRHIC ZDR authors EIC2006, Brookhaven National Laboratory, 17 July 2006. Hadron beam intensity limits. Outline. Parameters for ELIC and eRHIC Electron clouds Beam-beam effects Instabilities

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Hadron beam intensity limits

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  1. Wolfram Fischer Thanks to: M. Blaskiewicz, A. Fedotov, C. Montag, L. Merminga, V. Ptitsyn eRHIC ZDR authors EIC2006, Brookhaven National Laboratory, 17 July 2006. Hadron beam intensity limits

  2. Outline • Parameters for ELIC and eRHIC • Electron clouds • Beam-beam effects • Instabilities • Intrabeam scattering • Space charge • Resistive wall heating

  3. Not covered • Cooling of high energy ion beams[Talks by V. Lebedev, A. Zholents] – total p-beam currents in ELIC and eRHIC are comparable (~1A) • Polarization issues of protons and light ions • Injection, acceleration • IR, stored energy issues, beam loss at bmax[Talk J. Seeman, Tue 5:00-6:00pm Discussion] • Radiation safety • Technical challenges of crab cavities in ELIC[Session 3A, Tue 1:30-3:00pm Discussion]

  4. ELIC (linac-ring) Linac 200 MeV, pre-booster 3 GeV, booster 20 GeV

  5. EBIS BOOSTER AGS LINAC eRHIC (linac-ring) eRHIC detector beam dump e-cooling Place for doubling energy linac ERL (5-10 GeV e-) PHENIX RF STAR STAR For multiple passes: vertical separation of the arcs Wolfram Fischer

  6. ELIC and eRHIC parameters Use only limited number of parameter sets: • A linac-ring and a ring-ring version for both machines • Protons, mostly at highest energy (p bunches have largest no of charges, largest beam-beam parameter) • Beam parameters for highest luminosity

  7. with cooling without cooling ELIC and eRHIC parameters (p-beam only) [ELIC parameters courtesy of L. Merminga.]

  8. ELIC and eRHIC Both ELIC and eRHIChave versions with 10higher luminosity

  9. Selected machines with electron clouds [ECLOUD04 proceeding.]

  10. Selected machines with electron clouds less e-cloud more e-cloud

  11. RHIC e-clouds caused dynamic pressure rise S.Y. Zhang et al., EPAC06 • Dynamic pressure rise caused by electron clouds • Upgraded warm and cold vacuum system: • installed 430m of NEG pipes (~700m warm sections) • reduced pressure in cold section to 1e-7 Torr before cool-down • Dynamic pressure currently not a concern in operation

  12. Crossing transition with slowly ramping sc. Magnets(all ions except protons) Instability limits bunch intensities for ions (~1.5 – 2.01011 e ) Instability is fast (t =15 ms), transverse, single bunch gt-jump implemented Octupoles near transition Chromaticity control(need x-jump for higher bunch intensities)  Electron clouds can lower stability threshold, will gain more operational experience in next ion run J. Wei et al., HB2006 Longitudinal distribution after transverse instability (courtesy C. Montag) RHIC e-clouds can lower stability threshold

  13. E-cloud simulation for RHIC (2) CSEC (by M. Blaskiewicz) – requires cylindrical symmetry, faster than ECLOUD, POSINST RHIC warm, field free region, single beam Nb=2.01011, tb=108ns, lb=5ns, dmax = 2.1

  14. E-cloud simulation for RHIC (2) CSEC (by M. Blaskiewicz) – requires cylindrical symmetry, faster than ECLOUD, POSINST RHIC warm, field free region, single beam Nb=2.01011, tb=108ns, lb=5ns, dmax = 2.1

  15. Activated NEG E-cloud in current RHIC vs. eRHIC Nb=2.01011 36 ns (1 bucket) spacing Nb=1.01011 Nb=2.01011 108 ns (3 buckets) spacing Nb=1.41011 Expect serious e-cloud problems forNb=2.01011 and 36 ns bunch spacing (Analysis needed for warm double beam, and cold regions also.)

  16. Electron and ion effects in ELIC • CSEC shows no electron multipacting in ELIC • Bunches with short spacing and low bunch charge behave like coasting beam • ISR like problems possible • Electron accumulation from beam loss or rest gas ionization can lead to instabilities(need gaps and/or clearing electrodes) • Pressure instability(rest gas ionization, ion acceleration in beam potential, molecular desorption after ion impact on wall, etc.) [beam currents in ELIC 1A, ISR 60A]

  17. Slide from a talk by V. Dudnikov (2006) ISR, coasting proton beam, ~1972 (R. Calder, E. Fischer, O. Grobner, E. Jones) excitation of nonlinear resonances; gradual beam blow up similar to multiple scattering beam induced signal from a pick up showing coupled e-p oscillation; beam current is 12 A and beam energy 26 GeV 2x10-11 Torr, 3.5% neutralization, DQ=0.015 • Damped by extensive system of electrostatic clearing electrodes

  18. intensities beams go into collisions DQbb,tottunes split to avoidcoherent modes luminosity Beam-beam limitation (1) Current (Run-6) RHIC conditions • Current beam-beam induced tune spread in RHIC DQbb,tot = 0.012 • SPS, Tevatron reached DQbb,tot  0.025 • No hadron collider stores beam on resonances of order 10 or lower

  19. concurrent opswith p-collision could be beneficial 2 IPs is beyondexisting machines Beam-beam limitation (2)

  20. Beam-beam limitations (3) Coherent effects now observed in hadron rings (RHIC, Tevatron, HERA) could become operational problem for large x, few bunches beam-beam coupled First observationof coherent modesin hadron ring,RHIC, Jan 2002 More on coherent effects: J. Shi?

  21. Beam-beam compensation Head-on beam-beam compensation • Need electron beam (for p+), amplitude dependence of beam-beam force cannot be matched with magnets • 4-beam e+e machine DCI (~1970) not successful(failure usually attributed to coherent effects) • May become a task in US LARP Long-range compensation • E-lens in Tevatron (not yet used for bb compensation in ops)[V. Shiltsev et al.] • Wires (proposed for LHC, tested in SPS, planned tests in RHIC – US LARP)[J.-P. Koutchouk et al.] • Partial compensation with wire demonstrated in DAFNE[K. Milardi et al. EPAC06] More on beam-beam: J. Qiang, J. Shi

  22. Nb=2.01011 lb=15cm Growth time ~hrs(like current Au). Intrabeam scattering (1) Calculations byA. Fedotov, using Betacool. • Cooling of protons not yet fully assessed • [Did not find IBS calculations for ELIC.]

  23. Intrabeam scattering (2) IBS dominates lifetime over many other effects(competes with beam-beam + other nonlinearities): For p-beam in eRHIC: • Luminosity (burn-off): tL >> 100 h • Restgas inelastic scattering : tNb 200 h • Emittance growth from restgas scattering: te 15 h • Emittance growth from bb elast. scattering: te 2000 h Used RHIC II pp-calculations, BNL C-A/AP/235 (2006).

  24. Instabilities – single bunch Had stored p-bunches with Nb>21011 and Ip > 5A at injection. Most problematic at low energy, can use long bunches.Expect no fundamental problem.

  25. Instabilities – multi-bunch If no single-bunch instability, tune shifts from long-range wake fieldsmust be larger than tune shifts from short range wake fields • RHIC impedance model includes resistive wall, abort kickers, unshielded bellows. • May be too low by up to a factor 3 • Calculation for injection (worst case) tune shift relatively flat <5ms growth time, could be damped Expect no fundamental problem with multi-bunch instabilities in RHIC. [Can make similar argument for ELIC.] M. Blaskiewicz

  26. Space charge Parameters for low energy operation, keep bunch length ofhigh energy operation. May be problematic.

  27. Resistive wall heating [A. Ruggiero, S. Peggs, BNL RHIC/AP/46 (1994).] Heat load in beam pipe wall assuming same beam pipe as RHIC(stainless steel at 4K),could use Cu for reduction +possible e-cloud heat load, current capacity  0.5 W/m

  28. Summary Considered hadron beam limitations from: • Electron cloud • Beam-beam • Instabilities • Intrabeam scattering • Space charge • Resistive wall heating Of concern appear: • Electron cloud in RHIC for Nb=2.01011 and 36 ns bunch spacing • Beam-beam in ELIC with more than 2 IPs • Intrabeam scattering in RHIC (ELIC?) • Possibly space charge at low energies Significant challenges for cooling, crab cavities (ELIC)

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