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Andreas Streun, PSI LER-3, Oxford, July 8-10, 2013

The A nti- B end C ell for low emittance up to factor 2 lower emittance without J x -manipulation. Andreas Streun, PSI LER-3, Oxford, July 8-10, 2013. Classical TME cell Theoretical Minimum Emittance:.

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Andreas Streun, PSI LER-3, Oxford, July 8-10, 2013

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  1. The Anti-Bend Cell for low emittance up to factor 2 lower emittance without Jx-manipulation Andreas Streun, PSILER-3, Oxford, July 8-10, 2013

  2. Classical TME cellTheoretical Minimum Emittance: ProblemGet minimum bo, ho at center andperiodic solution (a = h’ = 0 at ends)  cell phase advance: m = 284.5° long cell, strong quads, large chroma...  bxbyh h = 1 / r F, L, h

  3. Deviations from minimum conditions F = e / emin Ellipse equation: Cell phase advance real cells: Dm< 180° F ~ 3...6

  4. The anti-bend cell concept • TME cell: too weak focusing of dispersion  add a small negative dipole: anti-bendDh’ = sin < 0 • quads only for beta-matching at moderate phase advance m. • TME optics at lower m ! • Side effects on emittance: • main dipole angle increased by | | • anti-bend at large H

  5. Anti-bend vs. TME cell simplified anti-bend cell bxbyh thin quad anti-bend main bend F b d m ~ 150°: lower emittance due to lower dispersion at comparable beta. ideal TMEat 284.5° thick lines: anti-bend thin lines: TME

  6. Jx adjustment h = dipole curvature = 1/ r • push Jx ~2 to get half emittance (e ~ 1 / Jx ) • h>0 h > 0 b2 < 0defocusing gradient bend • h>0 h < 0 b2 > 0focusing gradient anti-bend • convenient magnet design:anti-bend = half quadrupole SLS booster half quad

  7. Anti-bend cell Example half quad anti-bend-0.54° tuning quads 6.43° cell 2.4 GeV mx = 154.2°( = 3 / 7 ) my = 25.7° ( = 1 / 14 ) Comparison ABC TME e 258 739 pm Jx1.97 1.32 e·Jx508 975 pm L 2.75 2.50 m se 9.7 7.7 10-4 DE 7.7 6.3 keV sext. 7.5°, 110 cm TME cell 6.4°, 94 cm

  8. Compact low-emittance ring - DRAFT - • 845°8BA (7 cells), 85 m straights. • 2.4 GeV, 246 m circumference. • e = 228 pm, Jx =2.24, se= 0.107 %, DE=367 keV. • Bpoletip (T) for R=15 mm: bends 1.0, quads 0.8, sext 0.5, oct 0.1 DA and 24 mm  beam pipe

  9. Orbit bump Anti-bend from dipole downfeed in quadrupole. (TRACY simulation) known from Dp < 0 orbits !

  10. Conclusion • A small anti-bend provides the dispersion matching missing in the standard TME cell. • Almost factor 2 lower emittance compared to TME cell of same tune and same Jx. • Disadvantage: requires rather highcell tune ~ 0.42..0.44 (150..160°). • Anti-bend as half quad: set Jx ~ 2, and convenient magnet design.

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