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

2. 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 cm (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 GeV/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 m 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.

3. (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.

4. Bypass I Bypass II Bypass III Bypass IVe-
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.

5. 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
0-0.63
3416
6832 1
3417
6834 2
3418
6836 3
3419
6838 4
3420
6840
3421
6842
3422
6844
3423
6846
3424
6848

6. 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 2
3417
6832 1 3
3418
6834 4
3419
6836
3420
6838
3421
6840
3422
6842
3423
6844