1. Vertical Dogleg Options for the Ion Collider Ring
V.S. Morozov, Y. Nosochkov
JLEIC Weekly R&D Meeting
September 8, 2016
F. Lin

2. General Considerations
Doglegs for vertically stacking the electron and ion collider beam lines in the arc sections
Constraints
Cannot interleave net rotations about different axis to avoid breaking the figure-8 spin symmetry
Have to manage horizontal and vertical dispersions
Minimize total length and magnet strengths for a given size of the vertical step (in the following assumed to be 1 m, need engineering feedback)
Dogleg options
Single step, e.g. bend down + ~2 vertical betatron phase advance + bend up
Two step (á la CEBAF), e.g. down/up dipole step +  vertical betatron phase advance + down/up dipole step
Combined vertical and horizontal bends, e.g. down/up dipole step + horizontally bending section with  vertical betatron phase advance + down/up dipole step

3. Dogleg Option I: Single Step
Achromatic
Can provide relatively large vertical step size
Size dominated by the space necessary to accumulate the 2 vertical betatron phase advance  to reduce it, use 1.6 m long (2 x regular) quadrupoles with maximum gradient of 52.3 T/m at 100 GeV/c
Yuri: it may be worth inserting another quadrupole

4. Dogleg Option II: Two Step
Achromatic
More efficient for a relatively small vertical step size
Lengths of the dipole pairs contribute significantly to the total size
Use 1.6 m long (2 x regular) quads with maximum gradient of 50.0 T/m at 100 GeV/c

5. Dogleg Option IIa: Two Step
Yuri’s suggestion: use standard 90 cells with periodic beta functions with the same polarity dipoles placed 2 cells apart (i.e. 180 deg apart)
Bigger step with regular optics but longer

6. Dogleg Option III: Combined
Achromatic for vertical dispersion, matched directly to a regular arc FODO cell and suppresses horizontal dispersion
(-) Involves a larger number of quadrupole families
Provides horizontal bend of one regular arc FODO cell
More efficient for a relatively small vertical step size
Lengths of the dipole pairs contribute significantly to the total size
(+) May be a better geometric match to the electron beam line  smaller tunnel
Use 1.6 m long (2 x regular) quads with maximum gradient of 46.1 T/m at 100 GeV/c

7. Conclusions
All three dogleg options have comparable lengths for 1 m vertical step size
Need engineering feedback
Smaller step size would favor options II and III while larger step size would favor option I
Despite its relative complexity, option III has an important potential benefit of providing a better geometric match to the electron beam line
Need to wait for the next-iteration electron ring layout to make a selection