1. Page 1 Review 09/2010 Overview of MEIC Electron Collider Ring Yuhong Zhang

2. Page 2 Review 09/2010 Electron Collider Ring Design Goals A storage ring is capable of providing the following features Overall Electron energy 3 to 11 GeV Accepting and accumulating full energy injected electron beam from CEBAF (No requirement of further upgrade of 12 GeV CEBAF) Option of “top-off” current operation Geometric Be large enough to accommodate 3 IPs (detectors) and all necessary components including RF system, spin manipulating, polarimetry, injection/ejection Sharing a same (figure-8 shape) footprint with the ion collider ring of 60 (30) GeV/u protons (ions) Beam qualities Be able to store a high average current (up to 3 A) and high bunch repetition rate (up to 1.5 GHz) CW electron beam Be able to maintain a reasonable long beam life time Small transverse emittance and short bunch length

3. Page 3 Review 09/2010 Electron Collider Ring Design Goals (cont.) Polarization high (>80%) polarization over a reasonable long period of time (>10 min) Longitudinal spin direction at all interaction points Capability of spin flipping beam Be able to accommodate and self-polarizing positron beam Technical and cost-wise Limiting synchrotron radiation power density below 20 kW/m, and also minimizing total radiation loss for requiring less RF power Constructed with warm magnets Stability or operability Achieving high stability & operability through modulation optics design Consideration of beam control and diagnostics Large momentum acceptance and dynamical aperture

4. Page 4 Review 09/2010 Figure-8 Electron Collider Ring Footprint 3 rd IR (60 m) Spin Rotator (8.8°/4.4°, 50 m) 1/4 Electron Arc (106.8°, 117.5 m) Figure-8 crossing angle: 2x30° Experimental Hall (radius 15 m) RF (20 m) Spin Rotator (8.8°/4.4°, 50 m) IR (60 m) Injection from CEBAF Compton polarimeter (28 m) 1/4 Electron Arc (106.8°, 117.5 m) Circumferencem1000 Figure-8 crossing angledeg60 Symmetric arc sections4 Quarter arc lengthm117.5 Quarter arc anglesdeg106.8 Length of Long straightsm240 Length of short straightm20 Length of Spin rotatorm50 Bending angle in spin rotator deg13.2 Interaction regionm60 Compton Polarimetrym28 Ions from big booster

5. Page 5 Review 09/2010 EnergyGeV511 Circumferencem995 Revolution Timeμsμs3.3 Revolution FrequencyMHz0.3 Beam CurrentA30.13 Bunch frequencyGHz1.5 Bunch spacingm0.2 Number of bunches4975 Electrons per bunch10 1.250.054 Arc lengthm118.5x4 Total arc angledeg240x2 Dipole lengthm1.5 Bending radiusm36.5 Bending angledeg2.35 LatticeFODO Cell lengthm4.8 Dipole packing factor%62.5 EnergyGeV511 Total radiation powerMW6.1 Radiation Power/mkW/m20 Energy loss per turnMeV243 Damping time, longitudinalMs8.250.78 Turns2475232 Horizontal Emitt., unnorm, uncoupled nm5.526.5 Horizontal Emitt., unnorm.nm5.526.5 Horizontal Emitt., norm.μmμm53.5570 Vertical Emitt., unnorm.nm1.15.3 Vertical Emitt., norm.μmμm10.7114 Vertical emitt. /horizontal. emitt. 0.2 Energy spread10 -3 0.711.6 Bunch lengthmm7.55.7 Comprehensive Parameter Table

6. Page 6 Review 09/2010 Figure-8 Electron Ring Design Parameters EnergyGeV511 Betatron tune, horizontal Betatron tune, vertical Synchrotron tune0.0450.133 Arc radiusm57 Straights, long (IR)m240 Straights, short (snake)m20 RF frequencyGHz1.5 Harmonic number4969 Momentum compaction10 -3 33 Transition gamma17.4 Integrated RF voltageMV4.872 Synchronous phasedeg2530 RF momentum acceptance10 -3 410.6 Acceptance/spread5.66.7 Natural chromaticity, y56 EnergyGeV511 Beta-star, horizontalmm100 Beta-star, verticalmm10 Horiz. beam size at IPμmμm23.5 Verti. Beam size at IPΜmΜm4.7 Beta max, horizontalM425 Beta max, verticalm612 Horiz. beam size at 1 st FFmm1.5 Vert. beam size at 1 st FF,mm0.82 Beam-stay-clear/RMS size15 Aperture, horizontalcm2.25 Aperture, verticalcm1.2 Beam-beam tune shift, horiz.0.03 Beam-beam tune shift, vert.0.03 Touschek lifetimemin76>2500 S-T self polarization timemin1112.2

7. Page 7 Review 09/2010 Formation of Stored Beam in the Collider Ring 40 s < 3.3 ps (1 mm) 0.2 pC 0.67 ns (20 cm) 1.5 GHz 10-turn injection 33.3 μs (2 pC) 40 ms (~5 damping times) 25 Hz Microscopic bunch duty factor 5x10 -3 Macroscopic bunch duty factor 8.5x10 -3 From CEBAF SRF Linac Stored beam in collider ring Full energy injection from CEBAF 10-turn injection followed by phase space damping RingStored currentA3 Bunch frequencyMHz1497 Ring circumferenceμsμs3.3 Number of bunches4975 Bunch chargenC2 Electrons/bunch10 1.25 Pulse train rep. rateHz25 Pulse train durations40 Total pulse train1000 cathodeBunch duration (FWHM)ps~70 Bunch chargepC0.2 Electron/bunch10 6 1.25 Peak currentmA2.86 LinacBunch lengthmm1 Microscope duty circle10 -3 5 Macro duty circle during fill10 -3 0.85 Macro pulse aver. currentμAμA300 Average current during fillnA250

8. Page 8 Review 09/2010 More Topics Electron collider ring optics designAlex Bogacz RF systems for electron collider ringHaipeng Wang Electron beam stabilityByung Yunn Electron beam polarizationVasiliy Morozov

9. Page 9 Review 09/2010 Backup Slides

10. Page 10 Review 09/2010 Compton Polarimeter Layout chicane separates polarimetry from accelerator scattered electron momentum analyzed in dipole magnet measured with Si or diamond strip detector pair spectrometer (counting mode) e + e – pair production in variable converter dipole magnet separates/analyzes e + e – sampling calorimeter (integrating mode) count rate independent Insensitive to calorimeter response Geometry: Total dipole chicane length = 28 m Dipoles = 3 m long, 2T Electron beam deflection between dipoles 1-2 = 94 cm  scattered electron 6.7 cm (3.3 cm) from beam at endpoint at asymmetry zero crossing (green laser) Photon detector 54 m from laser-electron interaction point David Gaskell