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

Achieving High Luminosity MEIC design luminosity – L~ 6x10 33 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 (σ z ~ β*) to avoid hour-glass effect – Small bunch charge (< 3x10 10 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 over 2  cm -2 s -1 KEK BMEIC Repetition rateMHz Particles per bunch10 3.3/ /1.25 Beam currentA1.2/1.81/3 Bunch lengthcm0.61/0.75 Horizontal / vertical β*cm56/0.5610/2 (4/0.8) Luminosity per IP, cm -2 s (14.2) ( ): high-luminosity detector

IR Design Challenges Low  * is essential to MEIC’s high-luminosity concept Large size of extended beam  f  * = F 2 – 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

Compensation of 2 nd -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

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 –u x is anti-symmetric with respect to the center of the CCB –u y is symmetric –D is symmetric –n and n s are symmetric

Compensation of Main 2 nd -Order Terms 2 nd -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

Effect of Angular Spread Contribution of the angular spread to 2 nd -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

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

Figure-8 Collider Rings Geometrical matching of electron and ion rings (MAD-X survey) – L ion = m, L ele = 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

Designing CCB Design system such that

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

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

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

Electron Interaction Region Total length = 125 m

Summary of Electron Optics Parameters Electron beam momentumGeV/c5 Circumferencem Arc’s net benddeg240 Straights’ crossing angledeg60 Arc lengthm Straight section lengthm Maximum horizontal / vertical  functions m514 / 613 Maximum horizontal / vertical dispersion D x,y m0.745 / Horizontal / vertical betatron tunes  x,y 61.(501184) / 60. (526639) Horizontal / vertical chromaticities  x,y -226 / -218 Momentum compaction factor  0.57  Transition energy  tr Horizontal / vertical normalized emittance  x,y µm rad53.5 / 10.7 Maximum horizontal / vertical rms beam size  x,y mm1.68 / 0.82

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 = T/m 2

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

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

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

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

Ion Interaction Region Total length = 140 m

Summary of Ion Optics Parameters Proton beam momentumGeV/c60 Circumferencem Arc’s net benddeg240 Straights’ crossing angledeg60 Arc lengthm391.0 Straight section lengthm Maximum horizontal / vertical  functions m1864 / 2450 Maximum horizontal dispersion D x m1.78 Horizontal / vertical betatron tunes  x,y 25.(501184) / 21. (526639) Horizontal / vertical chromaticities  x,y -320 / -397 Momentum compaction factor  5.12  Transition energy  tr Horizontal / vertical normalized emittance  x,y µm rad0.35 / 0.07 At 20 GeV/c injection: Maximum horizontal / vertical rms beam size  x,y At 60 GeV/c: Maximum horizontal / vertical rms beam size  x,y mm 19 / / 1.6

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 = T/m 2

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