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Accelerator Design Summary

Accelerator Design Summary. There are presently two designs, eRHIC and ELIC. For eRHIC, the Ring-Ring option with an electron ring 1/3 the size of RHIC is the present point design, however, the Ring-Linac option will be maintained and developed.

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Accelerator Design Summary

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  1. Accelerator Design Summary • There are presently two designs, eRHIC and ELIC. • For eRHIC, the Ring-Ring option with an electron ring 1/3 the size of RHIC is the present point design, however, • the Ring-Linac option will be maintained and developed. • ELIC is a “green-field” design being optimized for spin preservation & handling and for potentially higher luminosity than eRHIC.

  2. eRHIC Ring-Ring e-cooling 5-10 GeV static electron ring recirculating linac injector RHIC EBIS BOOSTER AGS LINAC V. Ptitsyn, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  3. eRHIC Ring-Linac V. Litvinenko, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  4. Ion Linac and pre - booster IR IR Snake Solenoid 3 - 7 GeV electrons 30 - 150 GeV light ions CEBAF with Energy Recovery Beam Dump ELIC Layout L. Merminga, Jlab Ion Linac and pre Ion Linac and pre Electron Cooling - - booster booster IR IR IR IR Snake Snake Solenoid Solenoid 3 3 - - 7 GeV 7 GeV electrons electrons 30 30 - - 150 GeV light ions 150 GeV light ions Electron Injector CEBAF with Energy Recovery CEBAF with Energy Recovery Beam Dump Beam Dump U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  5. Design Parameter comparison U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  6. Presentations • We heard presentations on • Electron and ion sources and polarization (Farkondeh, Poelker, Roser, Derbenev & Dudnikov, Barber) • Cold and intense beams (Skrinsky, Kroc, Derbenev, Dudnikov) • Energy recovering linacs (Litvinenko, Calaga, Krafft) • “Luminosity” (Hoffstaetter, Wei, Lebedev, Montag, Hyde-Wright, Wang, Masuzawa) • I will emphasize the WG contributions U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  7. Sources • Polarized Proton & ion sources • BNL has the KEK-TRIUMF-BNL OPPIS • 1.6 mA (1E12 pp) H– @ 90% polarization • EBIS for 3He++ under development at BNL, 2E11, 70…75% polarization • Atomic-beam Ion Sources (ABS) may yield somewhat higher polarization at lower current • 2D source: 90% Pz and Pzzvs 50…60% • a 6Li+++ source also may be feasible. U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  8. Polarized D- and He++ ion sources EBIS test stand • Vector spin polarized D- ion beam in excess of 1.0 mA can be produced in the OPPIS, as well as in the atomic beam source with resonant plasma ionizer. • J.Alessi and A.Zelenski proposed to use an EBIS (Electron Beam Ion Source under development at BNL) for nuclear polarized 3He gas ionization to 3He++ ions. The polarized 3He will be produced by conventional technique of optical pumping in metastable states. The expected beam intensity is about 2•1011 3He++ ions/pulse, polarization 70-75%. T. Roser, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  9. Sources (cont’d) • Electron Sources • Irradiate a GaAs cathode with circular polarized laser light (≈800 nm) & collect pol e–. • Strained lattice & superlattice cathodes have largely overcome the surface charge limit (e.g. SLAC), => no issue for eRHIC ring-ring • For ring-linac, ELIC at issue are rep. rates for the laser, up to 100 MHz lasers now available, combination of power & rep. rate not yet. • Increase area on cathode to increase charge • eRHIC: using FEL => large-scale project U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  10. ELIC e-Beam Specifications 1/f C /c /c ~100 C c I CR CR Injector C = 1.5 km t I CR Circulator Ring t • Typical parameters; • Ave injector gun current 2.5 mA (and then 25 mA) • Micropulse bunch charge 1.6 nC • Micropulse rep rate 150 MHz (and then 1.5 GHz) • Macropulse rep rate ~ 2 kHz, 0.5 ms duration. M. Poelker, Jlab U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  11. Continuing Trend Towards Higher Average Beam Current JLab FEL program with unpolarized beam ELIC with circulator ring Ave. Beam Current (mA) First low polarization, then high polarization at CEBAF Year Source requirements for ELIC less demanding with circulator ring. Big difference compared to past talks. Few mA’s versus >> 100 mA of highly polarized beam. First polarized beam from GaAs photogun M. Poelker, Jlab U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  12. Polarization, e– • Electron polarization (eRHIC): • Significant progress has been made (10 GeV): • Feasible design for spin rotators incl. spin matching. • eRHIC electron ring spin tracking studies(incl. spin rotators, excl. detector) • may produce >80% polarization, pol≈20 min (small e– ring helps!) • will require excellent alignment & orbit correction (50µm rms) • at lower energy: some shift of pol. vector U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  13. ELIC Polarization vs Energy D. Barber, DESY U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  14. Polarization: ELIC, e– • “Figure 8” design elegant way to control spin • Polarization axis given by “controlled imperfection” (e.g. solenoid). • Smaller no. of snakes required • Potentially up to 4 IPs with longitudinal poln. U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  15. (Slide of Fig. 8 ring with snake) U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  16. Polarization:p • Polarized protons demonstrated in RHIC (30%) • dominated by AGS depolarization • AGS upgrade program to increase polarization • Development of helical spin rotators/snakes U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  17. Polarization survival in RHIC (store # 3713) T. Roser, BNL Acceleration and squeeze ramp Spin rotator ramp Some loss during accel/squeeze ramp (Tune too close to ¼) No loss during spin rotator ramp and during store U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  18. e-Cooling • eRHIC ring-linac and ELIC proposals require e-cooling to work. eRHIC ring-ring would profit • e-Cooling is necessary to • combat IBS (beam emittance) • shorten the bunches (5 mm for ELIC) • Can make flat beams (ELIC) • effect of IBS greatly reduced • All cooling schemes require high power electron beams (50…75 MeV, ≈1 A) • Factor 10 beyond FNAL Recycler cooler U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  19. Electron Cooling (cont’d) • Because of the high beam power involved • Electron ring & energy recovery are required. • Stringent requirements on beam quality & collinearity of e and p beams • “Hollow” electron beams may help reduce recombination rates (Skrinsky). • Highly ambitious R&D projects, Recycler experience will be invaluable. • BNL is launching R&D project to demonstrate feasibility for RHIC upgrade. U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  20. R. Calaga, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  21. Schematic Layout of the Recycler Electron Cooling T. Kroc, FNAL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  22. Energy Recovering Linacs • ERLs are essential in most scenarios • Directl: ELIC, eRHIC ring-linac • Indirect: in the electron cooler • Principle demonstrated in Jlab FEL at low energy, recently at CEBAF at 1 GeV, 80 µA. • High-current high-energy operation remains to be demonstrated • Cavities for high-current ERL are being designed. U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  23. R. Calaga, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  24. Luminosity Considerations • Everything else being equal, luminosity is prop. to I•/ß*. • The linac scenarios gain on e by allowing high tune shift (disruption) of the e– beam. • The ring-ring scenario somewhat makes up by higher I. • However, how much beam loss (e.g. from halo generation) can the energy recovery replenish? U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  25. Gedanken Experiment For round, equal sized beams, the following scaling applies: G. Krafft, Jlab • Comparing linac-ring colliders and ring-ring colliders, what can change for the better? • Maximum Ie/e is set by ION ring stability. The same in the two cases • eset by the physics. The same in the two cases • Minimum ß* is set by IR region design issues. Can it be too much better for linac-ring? Should not be any worse than for ring-ring • re is set by (God, Yahweh, Allah, …); YOU cannot change it • If there are to be luminosity enhancements to be found for linac-ring designs compared to ring-ring designs, they must arise because one is allowed to make the equivalent tune shift e bigger for linac-ring colliders. • Finding the physical phenomena that determine the maximum e are extremely important for evaluating the linac-ring idea. U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  26. Luminosity (cont’d) • Beam-beam simulations are underway to reach insight • Two approaches: • Coulomb Sum • PIC • Benchmark: HERA! U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  27. Simulated coherent modes G. Hoffstaetter, Cornell why? how ? + (From work with Jack Shi, KU) U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  28. Luminosity G. Krafft, Jlab U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  29. The electron beam parameters F. Wang, Bates U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  30. e-ring path length adj. requirement (with super-bends) *Total path length increase: ~4.47cm. * Linear rad. power at 10 GeV ~14kW/m -5 20cm 0 e-p(GeV) 5/250 10/250 10/50 Scratch of a “super-bend” for radiation enhancement at 5 GeV F. Wang, MIT Bates Red: normal bend Blue: center bend only y reduction ~ 20% (Compare to 10 GeV) U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  31. Intra-beam phenomena in RHIC • IBS: intra-beam small-angle Coulomb scattering  primary luminosity limiting factor in an heavy-ion storage ring Rutherford scattering cross section ~ Z4 / A2 J. Wei, BNL Luminosity degradation U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  32. Flat colliding beams equilibrium Multiple IBS Touschek scattering Ya. Derbenev, Jlab At low coupling, cooling results in flat beams x – emittance is determined by the IBS vs horizontal cooling y – emittance is limited by the beam-beam interaction ·Luminosityis determined by the beam area ·IBS effect is reduced by a factor of the beam size aspect ratio ·Cooling effect at equilibrium can be enhanced by flattening the electron beam in cooling section solenoid y x U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  33. IBS in the Tevatron V. Lebedev, FNAL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  34. Tevatron Measurements V. Lebedev, FNAL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  35. Crossing Angle • Non-zero crossing angle causes luminosity loss (geometry) and synchro-betatron coupling limiting intensity, thus luminosity. • “Crab crossing” aligns the bunches in space such that they collide head-on, albeit in a transversely moving system, thus allowing a crossing angle, simplifying IR design greatly. • 1st test of scheme likely at KEKB. • One cavity/ring only => c.o. for head of bunch is different than for tail, crabbing everywhere • Integral part of ELIC (100 mr crossing angle) U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  36. Superconducting Crab Cavity KEK Crab Cavity R&D Group K. Hosoyama, K. Hara, A. Kabe, Y. Kojima, Y. Morita, H. Nakai A. Honma, A. Terashima, K. Nakanishi MHI S. Matsuoka, T. Yanagisawa M. Masuzawa, KEK U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04 K.Hosoyama (MAC 2004)

  37. Short bunches also make feasible the Crab Crossing: SRF deflectors 1.5 GHz can be used to create a proper bunch tilt Crab Crossing for ELIC Ya. Derbenev, Jlab 2 U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  38. IR issues • IR design is critical for colliders • Electron beams esp. challenging due to handling of synchrotron radiation • It is imperative that detector and accelerator people work together to reach a feasible design • Physics equirements (e.g. small-angle detectors, low backgrounds) • Machine requirements (beam separation, focusing, vacuum) U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  39. C. Montag, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  40. C. Montag, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  41. V. Litvinenko, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  42. Physics Requirements • The IR design will need more physics input: • (C. Hyde-Wright, ODU) • Forward tagging • Hadron beam tagging • Recoil protons • Neutron detection • … • Most of these require detector access to small/zero angle, spectrometer magnets etc. U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  43. C. Hyde-Wright, ODU • First few elements in lattice should be designed with thought to detection of forward fragments • Compact detectors near 0deg can enhance physics program. U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  44. Electron-cloud effect • Positively charged beams are subject to electron-cloud formation & emittance blowup • ISR, PSR, B-Factories, RHIC, BINP rings,… • Solenoids work well in drift regions, but are unlikely to work in magnets. • Electron rings are not safe either: fast ion instability can affect even the linac scenarios. U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  45. Models of two-stream instability • The beam- induces electron cloud buildup and development of two-stream e-p instability is one of major concern for all projects with high beam intensity and brightness [1,2]. • In the discussing models of e-p instability, transverse beam oscillations is excited by relative coherent oscillation of beam particles (protons, ions, electrons) and compensating particles (electrons,ions) [3,4,5]. • For instability a bounce frequency of electron’s oscillation in potential of proton’s beam should be close to any mode of betatron frequency of beam in the laboratory frame. 1. http://wwwslap.cern.ch/collective/electron-cloud/. 2. http://conference.kek.jp/two-stream/. 3. G.I.Budker, Sov.Atomic Energy, 5,9,(1956). 4. B.V. Chirikov, Sov.Atomic.Energy,19(3),239,(1965). 5. M.Giovannozzi, E.Metral, G.Metral, G.Rumolo,and F. Zimmerman , Phys.Rev. ST-Accel. Beams,6,010101,(2003). V. Dudnikov, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  46. Instability in RHIC, from PAC03 V. Dudnikov, BNL U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  47. R&D issues for ELIC and LR-eRHIC • High intensity polarized and unpolarized electron gun • Currently a few mA • Up to 450 mA / 16nC • Currently a few 100 mA of polarized beam GaAs photo injector at 80% pol. • Up to 450 mA electron current at 80% pol. • Methods to overcome the surface charge limit for 16nC/bunch • Beam emittance control for 16nC/bunch and a large source diameter (14mm) • Test and improvement of cathode lifetimes • Electron Cooling at high energies • Currently a frew 100MeV, soon 8.9GeV/c pbar at the FNAL recycler • For LR-EIC: Cooling of Au or light ions up to 100GeV, p at 27GeV • New technology: ERL cooling + cooling with bunched e-beam • Limits to the ion emittance with e-cooling (especially vertically) and with all noise processes. • Allowable beam beam parameters for ions, especially with electron cooling G. Hoffstaetter, Cornell U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  48. R&D issues for ELIC and LR-eRHIC • IR design, detector integration, saturation in special magnets, optimization … • Halo development by beam disruption, especially at low electron energies • Impact of beam disruption on following IRs • Ion-beam dynamics with crab cavities • High current ERLs • Currently strong influence of small e-beam oscillations on p-emittance in HERA • Stabilization of the e-beam + influence on the ion beam • Current limits by multi-pass Beam-Breakup instability • CW operation of high filed cavities, stabilization, heat loss • Influence of HOMs with large frequencis (>2GHz) • R/Q and Q agreement with calculations including absorbers G. Hoffstaetter, Cornell U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  49. R&D specific to ELIC G. Hoffstaetter, Cornell • Spin resonances in Figure 8 rings • Stability of non-vertical polarization in figure 8 rings and in the ERL • Stable beam in a 100 turn circulator ring • Crab cavity R&D and crab cavity beam dynamics • Beam beam resonance enhancement when operating close to the hourglass effect • Limits to the bunch length, since this limits the beta function R&D specific to LR-eRHIC • 1kW FEL at 840nm • Heating of the cathod / problems associated with large spot size (14mm) • Production of very high polarized e-beam U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

  50. eRHIC Hirata-Keil coherent beam-beam modes Restriction on e- beam energy (pol, lumi) effect of different ion energy on electron orbit maximize no. of bunches in RHIC ELIC Parameters have been pushed into new territory… ß, lb, ring shape, crab crossing,… benefits of circulator ring vs “real” storage ring Issues for further Study • Both proposals: • Interaction region, at different energies, with spin rotators U. Wienands, 2nd EIC Wkshp, Jlab Accel. Design Summary, 15-Mar-04

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