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

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

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

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

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

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

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