Fanglei Lin JLEIC R&D Meeting, August 4, 2016 Alternate JLEIC Electron Collider Ring Designs --- Use New Magnets to Obtain a Small Emittance Fanglei Lin JLEIC R&D Meeting, August 4, 2016 F. Lin

Electron Ring Baseline Design Layout Circumference of 2154.28 m = 2 x 754.84 m arcs + 2 x 322.3 straights e- R=155m RF Spin rotator CCB Arc, 261.7 81.7 Forward e- detection IP Tune trombone & Straight FODOs Future 2nd IP 310 m 784 m

Summary of Baseline Design 2.2km electron collider ring was design reuse of PEP-II HER magnets mostly Two arcs are composed of 15.2m long FODO cells, dispersion suppression sections and spin rotators FODO cell and dispersion suppression (PEP-II magnets) dipole 5.4m, bending angle 2.8, bending radius 110.5m, sagitta 3.3 cm, 0.3 T @ 10 GeV, can reach 0.362 T @ 12 GeV with only ~0.2% saturation Quadrupole 0.56m, field gradient <13 T/m @ 10 GeV with saturation <0.4%, gradient ~14-15 T/m @ 12 GeV with saturation up to ~6% 108/108 x/y betatron phase advance in FODO cell Spin rotators have new dipoles, solenoids and quads (~25T/m @ 10 GeV). Straight FODO cells, tune trombone and matching sections use PEP-II 0.73m-long PEP-II quads and some new quads Chromaticity compensation block, RF sections and detector region use new dipoles and quads. Arcs contribute ~90% emittance and ~30-40% chromaticities.

Approaches of Reducing Emittance All following options have been investigated Optimizing of sections, such as matching section, spin rotator, etc., to reduce the emittance contribution (30%) Pros: do not change the optics of the rest of the ring, except some particular sections Cons: ~110m additional space and 16 quads are needed Adding (dipole) damping wigglers (50% @ 5 GeV) Pros: do not change the baseline design, fast damping Cons: need wigglers, more radiation power, larger energy spread (a factor of 2), high RF peak power if keep the same bunch length, not suitable at higher energies, may affect the polarization lifetime Offsetting the beam in quads (~ 7 to 8 mm) in arcs (48%) Pros: do not change the baseline design Cons: larger energy spread (a factor of 2), longer (maybe) bunch length, have to center the sextupoles New magnets (instead of PEP-II magnets) ring but still FODO cell arcs (50%) Pros: small dipole bending angle results in small emittance and no sagitta issue Cons: all new magnets, large chromaticities, strong sextupoles for chromaticity compensation due to small dispersion Different types of arc cell, such as DBA, TME (> 50%) Pros: much smaller emittance comparing to the FODO cell Cons: more quads, stronger quads, larger ring (possible), large chromaticities, chromaticity compensation scheme Need combine non-linear dynamic studies

New Magnet FODO Arc Cell e-Ring Complete electron collider ring optics circumference of 2181.89 m = 2 x 809.98 m arcs + 2 x 280.97 m straights

New Magnet FODO Arc Cell Arc FODO cell (Each arc has 54 such normal FODO cells) Length 11.4 m (half of ion ring arc cell) arc bending radius 155.45 m 108/108 x/y betatron phase advance Dipole Magnetic/physical length 3.6/3.88 m Bending angle 36.7 mrad (2.1), bending radius 98.2 m 0.34 T @ 10 GeV (0.41 @ 12 GeV) Sagitta 1.65 cm Quadrupoles Magnetic/physical length 0.56/0.62 m 17.5 T/m field gradients @ 10 GeV (21 T/m @ 12 GeV) 0.88 T @ 50 mm radius @ 10 GeV (1.06 T @ 12 GeV) Sextupoles Magnetic/physical length 0.25/0.31 m -624 and 262 T/m2 field strengths @ 10 GeV for chromaticity compensation of the whole ring 1.2 T and 0.5 T @ 60 mm radius @ 10 GeV (1.4 T and 0.6 T @ 12 GeV) BPMs and Correctors Physical length 0.05 and 0.3 m New Baseline

Comparison of e-Ring Parameters Baseline design (FODO arc cell) w/ PEP-II magnets Optimized baseline design (FODO arc cell) w/ PEP-II magnets New design (FODO arc cell) w/ new magnets Ring circumference m 2154 2186 2182 Bending angle per arc / figure-8 crossing angle deg 261.7 / 81.7 Beta stars at IP *x,y cm 10 / 2 Hor. / ver. chromaticities x,y -149 / -123 -113 / -120 -127 / -140 Momentum compaction factor  10-3 2.2 1.9 1.1 (reduce bunch length or V_peak ? ) Energy spread @ 5 and 10 GeV 10-4 4.6 / 9.1 4.5 / 9.0 4.6 / 9.3 Normalized emittance @ 5 and 10 GeV rad 137 / 1093 93 / 740 54 / 433 Hori. beam sizes at IP @ 5 and 10 GeV m 38 / 75 31 / 62 24 / 47 Arc FODO cell (2 dipoles, 2 quads per cell) length 15.2 (PEP-II cell length) 11.4 (half of ion ring arc cell) dipole length / sagitta m / cm 5.4 / 3.3 3.6 / 1.65 dipole bending angle / radius deg / m 2.8 / 110.5 2.1 / 98.2 quad length/strength @ 10 & 12 GeV m / T/m 0.56 / 13 / 15.6 0.56 / 17.5 / 21 cells per arc (including dispersion suppresser, no spin rotator) 42 44 58

Momentum Acceptance & Dynamic Aperture First look of momentum acceptance and dynamics aperture at 5 GeV by using 2 sextupole families for linear chromaticity correction only, no errors. Chromatic tunes and chromatic * Dynamic aperture (-7, +13)σp/p ±20 σx

New Magnet TME-like Arc Cell e-Ring Complete electron collider ring optics circumference of 2166.82 m = 2 x 786.08 m arcs + 2 x 297.33 m straights

New Magnet TME-like Arc Cell Arc TME-like cell (Each arc has 26 such normal TME-like cells) Length 22.8 m (same as ion ring arc cell) arc bending radius 155.45 m 270/90 x/y betatron phase advance Dipole Magnetic/physical length 4.0/4.28 m Bending angle 36.7 mrad (2.1), bending radius 109.1 m 0.31 T @ 10 GeV (0.37 @ 12 GeV) Sagitta 1.83 cm Quadrupoles Magnetic/physical length 0.56/0.62 and 1.0/1.06 m 20 T/m field gradients @ 10 GeV (24 T/m @ 12 GeV) 1.0 T @ 50 mm radius @ 10 GeV (1.2 T @ 12 GeV) Sextupoles Magnetic/physical length 0.25/0.31 m 400 and 604 T/m2 field strengths @ 10 GeV for chromaticity compensation of the whole ring 0.72 T and 1.08 T @ 60 mm radius @ 10 GeV (0.86 T and 1.3 T @ 12 GeV) BPMs and Correctors Physical length 0.05 and 0.25 m

Comparison of e-Ring Parameters Optimized baseline design (FODO arc cell) w/ PEP-II magnets New design (FODO arc cell) w/ new magnets New design (TME arc cell) w/ new magnets Ring circumference m 2186 2182 2167 Bending angle per arc / figure-8 crossing angle deg 261.7 / 81.7 Beta stars at IP *x,y cm 10 / 2 Hor. / ver. chromaticities x,y -113 / -120 -127 / -140 -152 / -150 Momentum compaction factor  10-3 1.9 1.1 (reduce bunch length or V_peak) 0.5 (reduce bunch length or V_peak) Energy spread @ 5 and 10 GeV 10-4 4.5 / 9.0 4.6 / 9.3 4.5 / 9.1 Normalized emittance @ 5 and 10 GeV rad 93 / 740 54 / 433 31 / 247 Hori. beam sizes at IP @ 5 and 10 GeV m 31 / 62 24 / 47 18 / 36 Arc TME-like cell (4 dipoles, 4 quads per cell) length 15.2 (PEP-II cell length) 11.4 (half of ion ring arc cell) 22.8 ( ion ring arc cell) dipole length / sagitta m / cm 5.4 / 3.3 3.6 / 1.65 4.0 / 1.83 dipole bending angle / radius deg / m 2.8 / 110.5 2.1 / 98.2 2.1 / 109.1 quad length/strength @ 10 & 12 GeV m / T/m 0.56 / 13 / 15.6 0.56 / 17.5 / 21 0.56, 1.0 / 20 / 24 cells per arc (including dispersion suppresser, no spin rotator) 44 58 28

Momentum Acceptance & Dynamic Aperture First look of momentum acceptance and dynamics aperture at 5 GeV by using 2 sextupole families for linear chromaticity correction only, no errors. Chromatic tunes and chromatic * Dynamic aperture (-12, +12) σp/p ±10 σx

Summary of Three Optics Designs ±20σx (-7.8, +5.6) σp/p Optimized baseline e-ring design with FODO arc cells (PEP-II magnets) ±20 σx (-7, +13)σp/p New magnet e-ring design with FODO arc cells ±10 σx (-12, +12)σp/p New magnet e-ring design with TME-like arc cells

Thank You for Your Attention !

Coupled Emittance In an electron storage ring without vertical bending and coupling, the natural horizontal emittance can be calculated by and the natural vertical emittance usually is a few orders of magnitude smaller than the horizontal one. A coupling effect can be introduced to a flat electron ring to obtain a non-flat beam. Assume the emittance coupling ratio k= y/x , then Here x,0 is the natural horizontal emittance. They satisfy x + y =x,0, and it has x/x,0=1/(1+k). JLEIC requires non-flat electron beams with k=y/x=1:5. Then x/x,0=0.83. I used the uncoupled natural horizontal emittance x,0 for the calculation of horizontal beam size, and x,0/5 for the calculation of vertical beam size. The beam sizes are overestimated by ~10%.