Progress in Testing a Hybrid Multi-Bend Achromat Lattice in JLEIC Electron Ring Fanglei Lin, Yuri Nosochkov Vasiliy Morozov, Yuhong Zhang, Guohui Wei JLEIC R&D Meeting, June 29, 2017 F. Lin

Outline Motivation Brief history of Hybrid Multi-Bend Achromat (HMBA) SuperB ESRF JLEIC HMBA design option Optics Emittance Estimated circumference Chromaticity budget Summary

Motivation / Application / Potential Issues Reduce the emittance of electron beam in the JLEIC electron collider ring Small emittance => reduce beam sizes at IP => boost the luminosity Small emittance => enlarge * => reduce maximum beta functions and beam sizes at FFQs => reduce FFQs’ apertures Hybrid Multi-Bend Achromat (HMBA) lattice Philosophy : dispersion bump for efficient chromaticity correction with less and relatively weak sextupoles Small dispersion and horizontal beta function on dipoles Application : SuperB and ESRF Expected potential issues Strong arc quadrupoles Long arc length

Super B From Yuri Nosochkov based on the latest SuperB HER lattice (per M. Biagini)

From Pantaleo Raimondi at IPAC’17

ESRF From Pantaleo Raimondi at IPAC’17

JLEIC HMBA Cell 1 HMBA cell 1 : L = 37.48 m,  = 225 mrad (12.89), HMBA cell bending radius is 166.58m ( 155.45 m in the baseline and short-arc-cell lattices) Dipole: total 8 dipoles Two 4.5m, 45mrad and six 2.25m, 22.5mrad All dipoles have the same bending radius of 100m (close to 110.5m in the baseline and 98.2 in the short-arc-cell lattices) Quadrupole, total 11 quadrupoles in 6 families Four 0.3 m and seven 0.5 m Maximum strength is ~17 T/m at 5 GeV with a pole tip field 0.83 T at 5cm radius Sextupole, total 4 in 2 families Two 0.15 m and two 0.3 m Strength will be determined BPM and Correctors Three 0.05m bpms and three 0.3 m H/V correctors Phase advances are H/V : 3 / 

Cell 1 Optics (H/V : 3 / ) SF SD

JLEIC HMBA Cell 2 HMBA cell 2 : L = 29.86 m,  = 135 mrad (7.74), HMBA cell bending radius is 221.19m ( 155.45 m in the baseline and short-arc-cell lattices) Dipole: total 6 dipoles Two 4.5m, 45mrad and four 1.125m, 11.25mrad All dipoles have the same bending radius of 100m (close to 110.5m in the baseline and 98.2 in the short-arc-cell lattices) Quadrupole, total 9 quadrupoles in 5 families Four 0.3 m, four 0.5 m and one 0.7 m Maximum strength is ~18 T/m at 5 GeV with a pole tip field 0.91 T at 5cm radius Sextupole, total 4 in 2 families Two 0.15 m and two 0.3 m Strength will be determined BPM and Correctors Three 0.05m bpms and three 0.3 m H/V correctors Phase advances are adjusted in two sets H/V : 2.5 / 0.5 (90) H/V : 2.6 / 0.6 (108)

Cell 2 Optics (H/V : 2.5 / 0.5) SF SD

Cell 2 Optics (H/V : 2.6 / 0.6) SF SD

Super HMBA Cell Optics Cell 1: 3 /  Cell 2: 2.5 / 0.5

Cell w/ Phase advance (H / V) Normalized Emittance (m) 3 GeV 5 GeV 10 GeV HMBA cell 1 : 3 /  2.2 10.1 80.9 HMBA cell 2 : 2.5 / 0.5 ( and 2.6 / 0.6 ) 1.4 (1.9) 6.5 (8.7) 51.6 (69.5) HMBA cell 1 + 2 1.9 (2.1) 8.7 (9.6) 69.9 (76.6) Short FODO cell : 0.6 / 0.6 10.0 46.4 371.6 Note that: The emittance is reduced by a factor of 5 for the HMBA cell. The total emittance will be finally determined (maybe dominated) by other sections (such as dispersion suppression, SBCCs, spin rotators) if they have relatively large contribution.

Estimated Geometry Super HMBA cell : cell 1 + cell 2 Length 67.34 m, bending angle 20.63 , average arc radius 187.06 m. Estimated one arc bending angle: 20.63x(8+2) + 17 + 26.4 = 249.7 then crossing angle is 69.7 Estimated one arc length: 67.34*10 + 104*2 + 75.2*2 = 1031.8 m IF each straight is ~220m, then the total circumference will be 2.5km. 2 spin rotators 2 SBCCs Disp. Supp. for injection and matching Sextupole pairs for chromaticity compensation 2 spin rotators 2 SBCCs

Optics of HMBA and FODO Cells

Cell w/ Phase Advance H / V Chromaticity Cell w/ Phase Advance H / V Chromaticity H / V HMBA cell 1 : 3 /  -2.27 / -1.44 HMBA cell 2 : 2.5 / 0.5 ( and 2.6 / 0.6 ) -1.64 / -1.59 (-1.85 / -1.39) HMBA cell 1 + 2 -3.91 / -3.03 (-4.12 / -2.83) Short FODO : 0.6 / 0.6 -0.44 / -0.44 Chromaticities per cell: HMBA/FODO ~ 9 Number of cells per arc : HMBA/FODO ~ 10/50 = 1/5 Number of sextupoles per arc : HMBA/FODO = ((4+4)*8)/((1+1)*40) =0.8 Beta functions * dispersion at sextupole locations (assume all sextupoles have the same length): SF : HMBA/FODO ~ 0.95 SD : HMBA/FODO ~ 0.8 Total chromaticity from cells only : HMBA/FODO ~ 1.8 Total optic compensation factor : HMBA/FODO ~ 0.64 - 0.76 The sextupole strengths in the HMBA cell will be 2.4 to 2.8 times stronger than those in the FODO cell. This may induce strong nonlinear motion and limit the dynamic aperture. Need study the chromaticity compensation scheme.

Summary A Hybrid Multi-Bend Achromat (HMBA) type optics design is explored for the JLEIC electron collider ring. The result, in term of reducing the emittance, is very promising. There is about a factor of 5 reduction, comparing to a FODO cell design. It requires strong quadrupole strengths and may, very possible, end up with a large circumference. It needs a chromaticity compensation study to demonstrate an adequate dynamic aperture.

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From Yuri on Jan 31, 2017

ρ = 61.5 m ρ = 61.3 m

ρ = 74.5 m ρ = 61.3 m