Present MEIC IR Design Status

1. Present MEIC IR Design Status Vasiliy Morozov, Yaroslav Derbenev MEIC Detector and IR Design Mini-Workshop, October 31, 2011

2. Achieving High Luminosity • MEIC design luminosity • L~ 6x1033 cm-2 s-1 for medium energy (60 GeV x 5 GeV) • Luminosity Concepts • Small β* (~5 mm) to reach very small spot sizes at collision points • Short bunch length (σz~ β*) to avoid hour-glass effect • Small bunch charge (< 3x1010 particles/bunch) for short bunches • High bunch repetition rate (0.5 GHz, can be up to 1.5 GHz) to restore high average current and luminosity • Crab crossing • Comparing to KEK-B and PEPII with already over21034cm-2 s-1 ( ): high-luminosity detector

3. IR Design Challenges • Low * is essential to MEIC’s high-luminosity concept • Large size of extended beam f * = F2 • Chromatic tune spread  limited momentum aperture • Chromatic beam smear at IP F ~ Fp/p >> *  limited luminosity  • Sextupole compensation of chromatic effects  limited dynamic aperture  compensation of non-linear field effects • High sensitivity to position and field errors

4. Compensation of 2nd-Order Terms • Consider parallel beam after extension, u describes the dominant (cos-like) parallel component of the trajectory while  is associated with the small remaining angular spread (sin-like trajectory), then, neglecting the angular divergence, one can approximate to obtain • In order to have the following conditions must be satisfied

5. Symmetry Concept • Modular approach: IR designed independently to be later integrated into ring • Dedicated Chromaticity Compensation Blocks symmetric around IP • Each CCB is designed to satisfy the following symmetry conditions • ux is anti-symmetric with respect to the center of the CCB • uy is symmetric • D is symmetric • n and ns are symmetric

6. Compensation of Main 2nd-Order Terms • 2nd-oder dispersion term and sextupole beam smear due to betatron beam size are automatically compensated. • Chromatic terms are compensated using sextupoles located in CCB’s attaining • local chromaticity compensation including contributions of both the final focusing quadrupoles and the whole ring • simultaneous (due to symmetry around IP) compensation of chromatic and sextupole beam smear at IP restoring luminosity

7. Effect of Angular Spread • Contribution of the angular spread to 2nd-order perturbation • Contribution to beam smear at IP is small compared to that of the parallel component u. However, it may dominate after compensation and its associated non-linear phase advance may affect the dynamic aperture. • Compensation conditions for the dominant sextupole terms • Considered CCB symmetry no longer helps. Possible approaches to compensation • additional symmetric sextupole families • compensation on a larger scale such over the whole IR or two IR’s

8. Interaction Region Geometry • Geometrical matching of electron and ion IR’s (MAD-X survey) • Weak bend for electrons to avoid emittance degradation • Strong bend for ions to generate large dispersion • Alternating bends in ion interaction region

9. Figure-8 Collider Rings • Geometrical matching of electron and ion rings (MAD-X survey) • Lion = 1340.92 m, Lele = 1340.41 m, can be adjusted • Ring separation < 4 m, can be reduced • Electron and ion IP’s coincide, crossing angle at IP’s = 60 mrad • Spin rotator geometry accounted for • Straight sections in the arcs for Siberian snakes

10. Designing CCB • Design system such that

11. Electron Final Focusing Doublet • Distance from the IP to the first quad = 3.5 m • Maximum quad strength at 5 GeV/c = 49.5 T/m

12. Electron Chromaticity Compensation Block • Meets symmetry requirements for the orbital motion and dispersion • Maximum quad strength at 5 GeV/c = 4.2 T/m

13. Electron Beam Extension Section • Matched to arc end on one side and to CCB on the other • Maximum quad strength at 5 GeV/c = 20.1 T/m

14. Electron Interaction Region • Total length = 125 m

15. Summary of Electron Optics Parameters

16. Electron Chromaticity Compensation • Two pairs of sextupoles placed symmetrically in each CCB • Sextupoles placed at points with large dispersion and large difference between horizontal and vertical beta functions • Sextupole polarity reverses together with dispersion • Maximum sextupole strength at 5 GeV/c = 281.4 T/m2

17. Electron Chromatic Tune Dependence • Electron ring’s momentum acceptance is not satisfactory • Small dispersion due to weak bends • Arc contribution to the chromaticity Optimization needed 5 p/p p/p = 0.710-3 at 5 GeV/c x,y < 0.02  2p/p

18. Ion Final Focusing Doublet • Distance from the IP to the first quad = 7 m • Maximum quad strength at 60 GeV/c = 175.1 T/m

19. Ion CCB • Meets symmetry requirements for the orbital motion and dispersion • Maximum quad strength at 60 GeV/c = 53.0 T/m

20. Ion Beam Extension Section • Matched to arc end on one side and to CCB on the other • Maximum quad strength at 60 GeV/c = 190.3 T/m

21. Ion Interaction Region • Total length = 140 m

22. Summary of Ion Optics Parameters

23. Ion Chromaticity Compensation • Two pairs of sextupoles placed symmetrically in each CCB • Sextupoles placed at points with large dispersion and large difference between horizontal and vertical beta functions • Sextupole polarity reverses together with dispersion • Maximum sextupole strength at 60 GeV/c = 391.8 T/m2

24. Ion Chromatic Tune Dependence 5 p/p p/p = 0.310-3 at 60 GeV/c x,y < 0.02  7p/p