MEIC beam path change with e-ring bypass lines J. Guo

MEIC Sync Options Revisit If “gear switch” is allowed: Each half of e-ring path (from IP to IP) length changes continuously in the range of 0-31.5cm (total range 0-63cm) Yuhong/Vasily have a chicane design Keep e-ring harmonic constant (3416 for 476MHz), jump ion ring harmonic number by 2 (from 6832 to 6848); adjust RF frequency by ±1.5×10-4. Two IPs for 952MHz e-ring, lose one IP at certain ion energies for 476 e-ring when i-ring harmonic number is 4N+2 (such as 6834, 6838, etc). If “gear switch” is not allowed: Keep e-ring to i-ring harmonic ratio constant at 1:2 (or 1:1 after e-ring 952 upgrade), jump i-ring harmonic by 2 (from 6832 to 6848), adjust RF frequency by ±1.5×10-4 Requires change half of e-ring path in range of 0-2.8m, total 0-5.6m, for 12-100GeV/u ions Use Yuhong/Vasily’s chicane for 2X 0~31.5cm continuous change, plus 2X(8X31.5cm) discrete path changes using bypass lines, totally 0-5.67m continuous range The bypass lines can be installed after the 1st run of MEIC, during which we can experimentally confirm whether gear switch is allowed or not.

(29m longer than regular straight) Bypass Line Design 31.24m (29m longer than regular straight) 4.96m Line 4 3 2 1 Bending magnet 4, 3, 2, 1, 1, 2, 3, 4 Total length ~90m Assumes 2.2m between B-mags except for the long straights 110.5m bend radius (to keep SR same) and 5.4m B-mag length, 2.8° bending angle for the ring B-mags Bypass line B-mags and switch mags have same 5.4m length but different bending angle and sagitta Beam path width at B4 exit: ~25cm Improvement and optimization needed. Line # B4 bending Angle (°) Change in path length (m) Mag 1-3 bending angle Δx max (m) Long straight length (m) 2.8 31.24 1 0.315 2.14 2*16.88 2 0.74 0.63 3.49 3.23 2*17.04 3 -0.97 0.945 4.06 4.15 2*17.19 4 -2.47 1.26 4.56 4.96 2*17.35 Line 2-4 are likely to operate at lower electron energy, so smaller bending radius is allowed without higher max energy loss per turn and emittance. Need to confirm with physics.

Bypass I Bypass II Bypass III Bypass IV e- R=155m RF Spin rotator CCB Arc, 261.7 81.7 IP Tune trombone & Straight FODOs Future 2nd IP Bypass III Bypass IV 4 bypasses in 4 quadrants, can turn on by pair, minimum change 2*0.315m=0.63m, max change 4*4*0.315=5.04m (5.67m including the 2*0.315m chicane, good for 11.9 GeV/u ion) To reduce the number of bends, We only need line 0, 4 in bypass III and IV. Or we can build line 0, 1, 3, 4 in bypass I, II and line 0, 4 in III, IV to make the bends less crowded. Need 60 additional bends (31% of original arc) , including 8 switching bend (wider). Can be staged. Total arc length 116m (~8%) longer, ~5% of circumference, if we keep the bending radius the same. If the bypasses are right next to the spin rotators, it will reduce the length of the long straights, so the total circumference will increase less than 116m; if the bypasses are located close to the center of arcs, it will significantly increase the length of the long straights and the circumference.

Ion Energy range (GeV/u) Path length change range (m) Use of bypass lines at different ion energy, no gear switch Ion Energy range (GeV/u) Line in bypass Path length change range (m) Harmonic Number I II III IV E-ring I-ring 35.26-100 0-0.63 3416 6832 25.53-35.26 1 0.63-1.26 3417 6834 20.93-25.53 2 1.26-1.89 3418 6836 18.12-25.53 3 1.89-2.52 3419 6838 16.17-18.12 4 2.52-3.15 3420 6840 14.72-16.17 3.15-3.78 3421 6842 13.59-14.72 3.78-4.41 3422 6844 12.67-13.59 4.41-5.04 3423 6846 11.9-12.67 5.04-5.67 3424 6848

Ion Energy range (GeV/u) Path length change range (m) Non-pair-wise collision (one ion bunch collides with all electron bunches), two IPs Ion Energy range (GeV/u) Line in bypass Path length change range (m) Harmonic Number I II III IV E-ring I-ring 35.26-100 2 0.63-1.26 3417 6832 25.53-35.26 1 3 1.26-1.89 3418 6834 20.93-25.53 4 1.89-2.52 3419 6836 18.12-25.53 2.52-3.15 3420 6838 16.17-18.12 3.15-3.78 3421 6840 14.72-16.17 3.78-4.41 3422 6842 13.59-14.72 4.41-5.04 3423 6844