JLEIC Collider Rings’ Geometry Options Fanglei Lin, Vasiliy Morozov

Electron Ring Design History 2011 September -2013 January : had a 1.3 km ring with one short in each arc for Siberian snakes. Developed and studied ion chromaticity compensation scheme and DA. 2013 January : completed a 1.2 km electron ring, shorts were removed from arcs. 2013 February : completed a 1.5 km (60 crossing angle) electron ring (considering to lengthen the polarization lifetime). 2014 June – December : studied various arc cell design options, decided to construct a FODO-arc-cell lattice reusing PEPII magnets. 2015 January : completed a 2.2 km (2154 m, 81.7 crossing angle) ring using PEPII magnets for the cost review. Dedicated CCB is included, but had a large emittance contribution. 2015 February – 2016 August : still a 2.2 (2185m) km ring but optimized optics to reduce the emittance, explored different chromaticity compensation schemes. 2016 September – 2017 April : studied DA for a TME-like lattice. 2017 April : completed a 2.3 km (2276 m) ring using new magnets with an optimum SuperB- like CCB design and studied DA (presented at JLEIC collaboration meeting spring 2017). 2017 October : completed a 2.3 km (2336m, 81.7 crossing angle) ring (the one in svn now). However, IP is very close to the figure-8 crossing point, ~35 m. 2018 March : completed a 2.5 km (2498 m, 69  crossing angle) ring and presented at JLEIC collaboration meeting spring 2018. The distance between IP and crossing point is ~100 m. 2018 March : geometrically completed a 2.4 km (2365m) ring at the JLEIC collaboration meeting spring 2018.

JLEIC Collider Ring Geometry 2.2 km : at cost review in Jan 2015 2.5 km : at JLEIC collaboration meeting spring 2018 2.4 km : quick modified version at JLEIC collaboration meeting spring 2018 2.5km 2.4km 2.2km Courtesy of Rusty Sprouse, David Fazenbaker

Exploration of Collider Ring Geometry Option Condition Circ. Figure-8 crossing angle Arc length Straight length IP to crossing angle To CEBAF m degree ft 1 Current spin rotator1 + current CCB + straight. CCB replaces the second dipole set in spin rotator. 2343 69 971 200 50 2 Current spin rotator, no CCB2. 2323 795 367 130 30 2.1 Current spin rotator, no CCB. 2232 77.4 818 298 100 3 New spin rotator3 + current CCB + straight. (see more info about new spin rotator in slide 6) 2327 67.8 986 178 40 20 4 New spin rotator, no CCB. 2273 825 312 120 5 New spin rotator + current CCB + straight. 2277 72 998 141 111 6 2186 76.2 848 245 70 Current spin rotator only rotates the spin. Vertical dogleg is still needed in the ion ring. Only global chromaticity compensation will be performed if no CCB. New spin rotator has two functions : i) rotating the spin ii) bringing the electron beam to the ion beam plane for collision. The total bending angles in the new spin rotator are zero in both horizontal and vertical planes.

1 (orange) 2 (green) 3 (blue) 4 (cyan) 5 (magenta) 6 (dark green) 2.154 km, 367ft to CEBAF Option 2.1 Option 6 and 2.1 (no CCB) are promising, but need nonlinear dynamic study. Option with CCB may deserve more exploration.

New Spin Rotator x : radial field y : vertical field z : longitudinal field Courtesy of Anatoly Kondratenko et al.

Summary of DA Study for a 2185m-long Ring (reuse PEP-II magnets) Chromaticity Correction Schemes x/x,0 DA: x/σx , y/σy Range of (p/p)/σ p/p=0 p/p=0.4% Linear correction: conventional 2-family arc sextupoles (v1) Non-linear: no dedicated correction 1 ±20, ±48 0, 0   9 Linear correction: conventional 2-family arc sextupoles Non-linear: interleaved –I sext pairs in regular arc cells (v1a) Non-linear: FODO type CCB with 2 non-interleaved –I sextupole pairs, optimized phase advance (v1b3) 2.1 ±15, ±40 ±4.5, ±10   9 Non-linear: FODO type CCB with 2 non-interleaved –I sextupole pairs, optimized phase advance, reduced beta functions for lower emittance (v1d2) 1.7 ±17, ±41 ±5, ±10 Non-linear: compact CCB with 3 interleaved sextupoles, optimized phase advance ±8.5, ±18 ±5, ±7.3 Non-linear: SuperB type scheme (SBCC) with regular length dipoles and large bending angles (scheme-3 ) 1.4 ±25, ±60 ±10, ±15 Non-linear: SBCC with short dipoles and small bending angles (scheme-6, optimized, ring geometry not yet matched) 0.93 ±23, ±72 ±7, ±26 11 Will consider chosen

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