1. EIC Users Meeting, SBU, 6/27/14 Polarized Electron Beams in the MEIC at JLab Fanglei Lin for MEIC Study Group EIC Users Meeting, Stony Brook University, June 27, 2014

2. EIC Users Meeting, SBU, 6/27/14 MEIC layout and electron polarization requirements MEIC electron polarization design ̶ Overview of strategies ̶ Initial Injection bunch pattern ̶ Polarization collision pattern and measurement ̶ Optimization of average polarization ̶ Continuous injection option Conclusions & Outlook Outline 2

3. EIC Users Meeting, SBU, 6/27/14 MEIC & e - Polarization Requirements 3 Three compact rings: 3 to 12 GeV electron Up to 25 GeV/c proton (warm) Up to 100 GeV/c proton (cold) Warm large booster (up to 25 GeV/c) Warm 3-12 GeV electron collider ring Medium-energy IPs with horizontal beam crossing Injector 12 GeV CEBAF Pre-booster SRF linac Ion source Cold 25-100 GeV/c proton collider ring Three Figure-8 rings stacked vertically Electron cooling Cross sections of tunnels for MEIC Ion Source Pre-booster Linac 12 GeV CEBAF 12 GeV 11 GeV IP MEIC collider rings Full Energy EIC Collider rings Electron cooling Electron polarization of 70% or above Longitudinal electron polarization at collision points Spin flipping

4. EIC Users Meeting, SBU, 6/27/14 Highly vertically polarized electron beams are injected from CEBAF –avoid spin decoherence, simplify spin transport from CEBAF to MEIC, alleviate the detector background Polarization is designed to be vertical in the arc to avoid spin diffusion and longitudinal at collision points using spin rotators Universal spin rotator rotates the electron polarization from 3 to 12GeV Desired spin flipping is implemented by changing the source polarization Compton polarimeter is considered to measure the electron polarization –Two long opposite polarized bunch trains (instead of alternate polarization between bunches) simplify the Compton polarimetry Polarization configuration with figure-8 geometry removes electron spin tune energy dependence Continuous injection of electron bunch trains from the CEBAF is considered to – preserve and/or replenish the electron polarization, especially at higher energies, and – maintain a constant beam current in the collider ring Spin matching in some key regions is considered if it is necessary Overview of e − Polarization Strategies 4 … … … … Empty buckets 1.33ns 748.5MHz Polarization (Up) Polarization (Down) bunch train & polarization pattern

5. EIC Users Meeting, SBU, 6/27/14 Initial Injection Bunch Pattern 5 …… 200 us I ave = 82.6 nA Macro bunch train 100 ms (~21740 turns) Beam energyGev3567912 Beam current A 332.01.10.40.13 Injection time min 2.8 1.91.00.40.12 Such injection bunch pattern needs no upgrade of CEBAF beyond 12 GeV upgrade …… 1.33 ns, 748.5 MHz 2.4 pC 2.3μs, ~1700 bunches (I ave = 1.8 mA) half ring injection 2.4 pC 1.33 ns, 748.5 MHz 2.3μs, ~1700 bunches …… half ring injection

6. EIC Users Meeting, SBU, 6/27/14 HERA: –Each ion bunch only sees the same electron bunch MEIC: –Each ion bunch sees all electron bunches –No non-colliding bunches Polarization Collision Pattern 6 ion electron ion electron Therefore, in the MEIC –Bunch-to-bunch variation does not contribute to the uncertainty –One can measure average polarization of each macro bunch train

7. EIC Users Meeting, SBU, 6/27/14 Polarization Measurement 7 Compton polarimetry: (next talk given by Alexandre Camsonne) –same polarization at laser as at IP due to zero net bend Spin dancing (using spin rotators): –Experimentally optimize (calibrate) longitudinal polarization at IP c Laser + Fabry Perot cavity e - beam Quasi real photon tagger Quasi real photon tagger Electron tracking detector Photon calorimeter IP forward ion detection forward e - detection final focusing elements e-e- ions IP Arc Schematic drawing of USR Illustration of spin rotation by a USR

8. EIC Users Meeting, SBU, 6/27/14 Optimization of Average Polarization 8 Average Pol. : Initial polarization : Injection time : Depolarization time : Measurement time Energy (GeV)  inj (min)  meas (min) (P ave /P i ) max * 52.8120.82 7150.83 90.42.30.85 120.120.60.85 * Includes duty factor

9. EIC Users Meeting, SBU, 6/27/14 Continuous Injection Option 9 Lost or Extracted P 0 (>P t ) PtPt …… 1.33 ns, 748.5 MHz 2.4 pC 2.3μs, ~1700 bunches 2.4 pC 1.33 ns, 748.5 MHz 2.3μs, ~1700 bunches …… 200 us I ave = 33 nA 250 ms P ave /P 0 = 92% Continuous injection principle Low injected current preserves high polarization One possible injection bunch pattern –Damping time at energy > 5 GeV << 250ms –No beam dump needed

10. EIC Users Meeting, SBU, 6/27/14 Electron polarization schemes have been developed –Initial injection bunch pattern –Polarization collision pattern and measurement –Optimization of average polarization –Continuous injection option Outlook –Scheme or technique optimization –Spin matching to improve polarization lifetime –Spin tracking with realistic errors Acknowledgements –Y.S. Derbenev, J. Grames, J. Guo, L. Harwood, V.S. Morozov, P. Nadel- Turonski, F. Pilat, R. Rimmer, M. Poelker, R. Suleiman, H. Wang, S. Wang, Y. Zhang, – JLab –D. P. Barber – DESY/Liverpool/Cockcroft –M. Sullivan  SLAC Conclusion and Outlook 10

11. EIC Users Meeting, SBU, 6/27/14 Thank You for Your Attention 11

12. EIC Users Meeting, SBU, 6/27/14 Injection Bunch Pattern 12 …… 200 us I ave = 82.6 nA Macro bunch train duty factor 4.3e-4 …… 1.33 ns, 748.5 MHz 2.4 pC 2.3μs, ~1700 bunches (I ave = 1.8 mA) 2.4 pC 1.33 ns, 748.5 MHz 2.3μs, ~1700 bunches …… 100 ms (~21740 turns) Beam energyGev3567911 vertical damping timems167.236.220.813.26.23.4 Beam energyGev3567911 Beam current A 332.01.10.40.18 Injection time min 2.8 1.91.00.40.2