MEIC Electron-Ion Collider - Space-Charge Issues

Transcription

1 MEIC Electron-Ion Collider - Space-Charge Issues on behalf of MEIC Collaboration 1

2 MEIC (Medium-energy Electron Ion Collider) Collaboration A. Bogacz, P. Brindza, A. Camsonne, E. Daly, Y. Derbenev, D. Douglas, R. Ent, D. Gaskell, J. Grames, J. Guo, L. Harwood, A. Hutton, K. Jordan, A. Kimber, G. Krafft, R. Li, F. Lin, T. Michalski, V. Morozov, P. Nadel-Turonski, F. Pilat, M. Poelker, R. Rimmer, Y. Roblin, T. Satogata, M. Spata, R. Suleiman, A. Sy, C. Tennant, H. Wang, S. Wang, H. Zhang, Y. Zhang, Z. Zhao, (JLab), Newport News, VA USA P. Ostroumov, Argonne National Laboratory, Argonne, IL USA S. Abeyratne, B. Erdelyi, Northern Illinois University, DeKalb, IL USA C. Hyde, K. Park, Old Dominion University, Norfolk, VA USA Y. Cai, Y. Nosochkov, M. Sullivan, M-H Wang, U. Wienands, SLAC National Accelerator Laboratory, Menlo Park, CA USA T. Mann, P. McIntyre, N. Pogue, A. Sattarov, Texas A&M University, College Station, TX, USA D. Barber, Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany A. Kondratenko, M. Kondratenko, Sci. & Tech. Laboratory Zaryad, Novosibirsk, Y. Filatov, Moscow Institute of Physics and Technology and Budker Institute, Dubna, Russia 2

3 Overview Collider design goals Physics case for Electron-Ion Collider High-luminosity design strategy for MEIC Accelerator complex overview Space-charge issues and mitigation schemes: Ion Linac Ion Booster Conclusions 3

4 MEIC Design Goals Energy Full coverage of s from 15 to 65 GeV Electrons 3-10 GeV, protons GeV, ions GeV/u Ion species Polarized light ions: p, d, 3 He, and possibly Li Un-polarized light to heavy ions up to A above 200 (Au, Pb) Luminosity to cm -2 s -1 per IP in a broad CM energy range Polarization At IP: longitudinal for both beams, transverse for ions only All polarizations >70% Figure-8 topology for all rings ease of spin manipulation Spin precessions in the left & right parts of the ring are exactly cancelled Net spin precession (spin tune) is zero, thus energy independent Spin is easily controlled and stabilized by small solenoids, or other compact spin rotators 4

5 Physics Case - Why We Need EIC The origin of nucleon spin and the distributions of quarks and gluons in nuclei remain mysteries after decades of study. A new facility, EIC, with a versatile range of kinematics, beam polarizations, and beam species, is required to precisely image the sea quarks and gluons in nucleons and nuclei, to explore the new QCD frontier of strong color fields in nuclei, and to resolve outstanding issues in understanding nucleons and nuclei in terms of QCD. Understanding the 99%, the glue that binds us Tomography of the nucleus Gluon and sea quarks spin orbital angular momentum EIC 3D imaging of sea quarks and gluons CEBAF 12 3D imaging of valence quarks 5

6 MEIC Complex - Baseline Layout Electron-Ion Collider Rings IP 8 GeV Booster SRF Linac to 285 MeV Ion Sources Future IP 3-10 GeV 8 to100 GeV Electron Injector 12 GeV CEBAF 5.5-pass CW RLA 3-10 GeV Hall D Halls A, B, C 6

7 Jefferson Lab Campus Layout 7

8 MEIC Design Strategy for High Luminosity High bunch repetition rate of CW colliding beams nn 1 2 ~ L f cm s * * 4 x y MEIC Beam Design Large number of bunches (high collision frequency f) Low bunch charge (n 1 and n 2 ) Short bunches Small beta-star Traditional Hadron Colliders Small number of bunches (low collision frequency f) High bunch charge (n 1 and n 2 ) Long bunches Large beta-star 8

9 MEIC Space-Charge Mitigation Strategy High bunch repetition rate (476 MHz) Limits bunch charge, while allowing higher average current Increased bunch length to store more charge in a bunch hour glass luminosity reduction Superconducting linac with a warm front-end to provide fast acceleration of ion beams, with individual velocity profiles for multiple-charge, light and heavy ions maximize individual injection energies of into the booster for variety of ion species: 280 MeV for H MeV/u for Pb 67+ Minimize direct space-charge effect (strongest for H - ) improved current and emittance of the injected beam into the booster Dn sc = r lc 0 Z 2 4pbg 2 e n A = r 0 Q Z 4pbg 2 e n A, Q = lcz 9

10 Collider Luminosity Parameters CM energy GeV 21.9 (low) 44.7 (medium) 63.3 (high) p e p e p e Beam energy GeV Collision frequency MHz Particles per bunch Beam current A Polarization % >70% >70% >70% >70% >70% >70% Bunch length, RMS cm Norm. emitt., vert./horz. μm 0.5/0.5 74/74 1/ /72 1.2/ /576 Horizontal and vertical β* cm 3 5 2/4 2.6/1.3 5/ /1.2 Laslett tune-shift small 0.01 small 0.01 small Hour-glass (HG) corr Lumi./IP, w/hg corr cm -2 s e d 3 He C Ca Pb 82+ Beam energy GeV Particles/bunch Beam current A Polarization >70% > 70% > 70% Bunch length, RMS cm Norm. emit., horz./vert. μm 144/72 0.5/ / / / /0.25 Laslett tune-shift Lumi/IP/nucleon, w/hg corr cm -2 s * Parameters are still evolving. 10

11 Ion Injector Complex 8 GeV Booster SRF Linac to 285 MeV Ion Sources Present status of the ion injector complex: Relies on demonstrated technology for injectors and ion sources Adopted an SRF linac design (al FRIB) 8 GeV Booster design avoiding transition crossing with all ion species (configured with super-ferric magnets) 11

12 Evolution of Beam Parameters: Polarized Protons (units) *ABPIS Source Linac Booster Entrance Injection Extraction Charge status H - H - H - H + H + Kinetic energy MeV ~ g b Pulse current ma Pulse length ms Charge per pulse μc Protons per pulse Pulses 1 *ABPIS - Atomic Beam Polarized Ion Source 12

13 Evolution of Beam Parameters: Ions (e.g. Pb) (units) *EBIS Source Linac After stripper Injection Booster After acceleration Charge status 208 Pb Pb Pb Pb 67+ Kinetic energy MeV/u ~ g b Pulse current ma Pulse length ms Charge per pulse μc Ions per pulse Pulses 28 * EBIS - Electron Beam Ion Source 13

14 Ion Source Options Ions Source Type Pulse Width Rep. Rate Pulsed Current Ions/pulse Polarization Emittance (90%) μs Hz ma π μm rad H - /D - ABPIS (10) 1000 > 90% 1.0 / 1.8 H - /D - ABPIS / / He ++ ABPIS % 1 3 He ++ EBIS (10) 70% 1 6 Li +++ ABPIS % 1 Pb 30+ EBIS (1.6) 0.3 (0.5) 0 1 Au 32+ EBIS (1.7) 0.27 (0.34) 0 1 Pb 30+ ECR (1) 0 1 Au 32+ ECR (0.6) 0 1 ABPIS - Atomic Beam Polarized Ion Source EBIS - Electron Beam Ion Source ECR - Electron Cyclotron Resonance 14 14

15 Warm/Cold Ion Linac - Current Baseline RFQ QWR QWR HWR Ion Sources IH 4 cryostats 2 4 cryos 2 cryos cryostats MEBT Optimum stripping energy: 13 MeV/u Linac design based on the ANL linac for FRIB Pulsed linac capable of accelerating multiple charge ion species (H - to Pb 67+ ) Warm Linac Sections (115 MHz): RFQ (3 m) MEBT (3 m) IH structure (9 m) Cold Linac Sections: QWR + QWR (24 m + 12 m) stripper, chicane (10 m) HWR section (60 m) 115 MHz 115 MHz 230 MHz Ion species: p to Pb Ion species for the reference design Kinetic energy (p, Pb) Maximum pulse current: Light ions (A/Q<3) Heavy ions (A/Q>3) Pulse repetition rate Pulse length: Light ions (A/Q<3) Heavy ions (A/Q>3) Maximum beam pulsed power Fundamental frequency Total length 208 Pb 285 MeV 100 MeV/u 2 ma 0.5 ma up to 10 Hz 0.50 ms 0.25 ms 680 kw 115 MHz 121 m 15

16 Radio Frequency Components RFQ Segment IH Structure SRF Cavities QWR HWR 16

17 Medium Energy Beam Transport (MEBT) x x y x Q1 Q2 Q3 Q4 Buncher y x Df y L= 995 mm Df y DW/W Quadrupole Parameters Eff. Length (mm) Gradient (T/m) Q Q Q Q rms beam envelope matching required Cavity Voltage Frequency Length Buncher Parameters Quarter Wave 0.8 MV 115 MHz 340 mm DW/W 17

18 Superconducting Ion Linac SC linac provides superior flexibility to maximize energies for multiple charge ion beams (from H - to 208 Pb 67+ ). SC linac can provide 100 MeV/u for lead ions. In the same SC linac, an H - beam can reach 280 MeV, which is high enough to suppress space-charge in the booster (space-charge is most severe for the lowest mass-to-charge ratio, i.e. H - ) Single 2-gap SC cavity can provide significantly higher (factor of 10) voltage per cavity compared to room temperature cavities. High-Q (power ~ voltage 2 ) much higher peak fields available with SC cavities. 18

19 Voltage (MV) Voltage Gain per SC Cavity Final Energies Voltage (MV) Pb H b b Q ion source Energy at the stripper Q after the stripper Total energy MeV/u MeV/u Proton Dueteron Ar Xe Pb

20 Warm Ion Linac? If one built a room temperature linac with standard technology for 100 MeV/u lead ions (the same total voltage as for SC linac), one could only get 100 MeV protons. To achieve similar performance, as with SC cavities (compensate 10 times lower voltage per cavity), one would need to build factor of 10 more room temperature cavities and power amplifiers this will be quite expensive. In practice one could build 3-4 gap cavities to reduce their number. Even if one reduced number of cavities, one would still need higher power amplifiers to dissipate power in copper structures. The net length of cavity gaps sets the time-of-flight through the accelerating structure, so that ALL ion species have to be accelerated with the same velocity profile along the linac one will achieve the same energy per nucleon for all ions (including protons). 20

21 Ion Linac Space-Charge Issues The space-charge effects are significant only in the injection beam-lines from the ion sources. Usually, emittance after both ECR and EBIS are not simple ellipses, beam collimation is required before transferring ions into the linac. Following the RFQ there are no sizable space-charge effects especially, if ECR sources are used for ion beam generation. The peak current from ECR will be less than 1-2 ma. If EBIS is used, the peak current can reach ~5 ma. The above level of peak currents can be handled with standard rms matching except the beam-lines after the ECR or EBIS (collimation required). 21

22 0-7 BETA_X&Y[m] DISP_X&Y[m] 70 7 Booster (8 GeV, g t = 10) Ring circumference: 273 m ( 2200/8) E kin = 285 MeV GeV Injection: multi-turn 6D painting ms long pulses ~180 turns g t M 56 = S M ò 56 D r ds Crossing angle: 75 deg. RF cavity extraction injection Proton single pulse charge stripping at 285 MeV Ion 28-pulse drag-and-cool stacking at ~100 MeV/u Ion energies scaled by mas-to-charge ratio to preserve magnetic rigidity M cm 0 BETA_X BETA_Y DISP_X DISP_Y Inj. Arc (255 0 ) Straight Arc (255 0 ) Straight (RF + extraction) 22 22

23 0 0 BETA_X&Y[m] DISP_X&Y[m] 30 3 Arc Cell - Super-ferric Magnets 0 BETA_X BETA_Y DISP_X DISP_Y Bend Sextupole Dual-dipole Bend Half-cell cryomodule Magnet aperture radius: 6 rms = 42 mm Quad Bend: L b = 120 cm (magnetic length) Lead ends: 2 22 cm B = 2.73 Tesla bend ang. = 7.08 deg. Sagitta =1.8 cm Sextupole: L s = 10 cm S = 750 Tesla/m 2 Correctors BPM Quad Quadrupole: L q = 40 cm G = Tesla/m Correctors (H/V): 10 cm BPM can: 10 cm 23 23

24 Booster Ring Parameters Proton beam energy (total) GeV Circumference m Arc s net bend deg 255 Straights crossing angle deg 75 Arc length m 86.9 / 77.9 Straight section length m 53.8 Maximum hor. / ver. b functions m 60 / 38 Maximum hor. dispersion m 5.9 Hor. / ver. betatron tunes x,y 9.87 / 8.85 Hor. / ver. natural chromaticities x,y -28 / -24 Momentum compaction factor 10-2 Hor. / ver. normalized emittance x,y µm rad 2.7 / 2.7 Beam current Amp 0.2 Laslett tune shift at injection (protons)

25 0-5 BETA_X&Y[m] DISP_X&Y[m] 30 5 Ion Injection Transverse Phase-space Painting Doublet straight a la G. Rees D x b x Dp p >> e x e x» 10-3 m 1/2, D x b x = 4m 4m = 2m1/2 Dp p» m 31.8 BETA_X BETA_Y DISP_X DISP_Y 55 25

26 Adiabatic Capture and Acceleration (h =1) protons H Pb 67+ Energy GeV RF Frequency Range MHz Ramping Time sec lead ions 26

27 0-7 BETA_X&Y[m] DISP_X&Y[m] Tune Diagram Space-charge Footprint? Table 1 Dipole, multipoles in units of 10-4, reference radius at 1.5 cm Q y Q x/y = 9.87 / 8.85 I scale b 0 (T) b 2 b 4 b 6 b 8 b mod Q x Nominal current 15kA (I scale =1) Table 2 Quad multipoles, reference radius 3 cm I scale b 1 (T/m) b 5 b 9 B mod Tracking for turns BETA_X BETA_Y DISP_X DISP_Y

28 Booster - Space-Charge Issues Laslett tune shift at injection (285 MeV): Present baseline: 0.1 (for 0.2 Amp coasting beam) Consider more aggressive current ~ 0.3 Amp Resonance crossing and stop-band corrections I. Hofmann GSI G. Franchetti FAIR If the incoherent space-charge tune shift at injection is large, > 0.3, significant fraction of particles in the beam can move cross third-integer and quarter-integer resonance lines. Properly placed quadrupoles and sextupoles could be used to correct the stop-band width of those resonances to minimize the amplitude growth and hence the beam loss. Halo generation beam collimation required 28

29 Summary Space-charge mitigation by design MEIC high-luminosity strategy: High bunch repetition rate of CW beams limits bunch charge and allows higher average current. Ion Sources: ABPIS (polarized light ions), EBIS (un-polarized heavy ions) Superconducting Ion Linac with warm front-end (based on FRIB design) Injected ion emittance are not simple ellipses beam collimation required Following the RFQ and MEBT sections, where the rms matching technique is required, there are no sizable space-charge effects for the rest of the linac. 8 GeV Booster design avoiding transition crossing for all ion species Laslett tune shift at injection (present baseline): 0.1 (0.2 Amp coasting beam) If more aggressive current considered ~ 0.6 Amp, then the resonance stop-band corrections required for space-charge tune shift larger than 0.3. Thorough space-charge studies required to optimize the present design 29

30 Thank you! Collaborators Welcomed 30

31 Backup Slides 31

32 12 GeV Upgrade Project Upgrade is designed to build on existing facility: vast majority of accelerator and experimental equipment have continued use Add 5 cryomodules New Hall Upgrade arc magnets and supplies The completion of the 12 GeV Upgrade of CEBAF was ranked the highest priority in the 2007 NSAC Long Range Plan. 20 cryomodules Add arc CHL upgrade Add 5 cryomodules 20 cryomodules Maintain capability to deliver lower pass beam energies: 2.2, 4.4, 6.6. Enhanced capabilities in existing Halls Scope of the project includes: Doubling the accelerator beam energy New experimental Hall and beamline Upgrades to existing Experimental Halls 32

33 Beam Formation Cycle 1. Eject the expanded beam from the collider ring, cycle the magnet 2. Injection from the ion linac to the booster 3. Ramp to 2 GeV (booster DC cooling energy) 4. DC electron cooling 5. Ramp to 8 GeV (booster ejection energy) 6. Inject the beam into the collider ring for stacking 7. The booster magnets cycle back for the next injection 8. Repeat step 1 to 6 for 8 times for stacking/filling the whole collider ring 9. Cooling during stacking in the collider ring 10. Ramp to the collision energy (20 to 100 GeV) 11. Coasting/re-bunching (or bunch splitting) to the designed bunch repetition rate Total formation time: 30 min 33