1. Thomas Jefferson National Accelerator Facility Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Issues for Formation of MEIC Ion Beam MEIC Ion Complex Design Mini-Workshop JLab, January 27-28, 2011 Ya. Derbenev

2. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 2 O u t l I n e Concept of high luminosity Required parameters, concepts and problems of : - High energy EC for EIC -Synchronization for EC- - Beam emittance injected in collider ring (required) - Luminosity lifetime (due to IBS and other) - Crab Crossing - Acceleration/rebunching in collider ring - Synchronization for collisions- - Emittance vs space charge at stacking - Beam loss at re-bunching - Microwave beam stability (wakes in SRF cavities and other) - Electron cloud - Gaps

3. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 3 Luminosity in colliders with Electron Cooling Decrease the bunch length  design low beta-star Decrease transverse emittances   design low beta-star Raise the beam-beam tune shift limit: large Q s (exceeding bb tune shift) Raise repetition rate by arrangement for crab crossing to eliminate the parasitic bb -Crab crossing is effective at HF- matches short bunches ! Decrease charge/bunch- receive MW stability, reduce IBS Diminish the IBS using flat beams (non-coupled optics) EC in cooperation with strong HF SC field allows one to obtain: Very short ion bunches (1cm or even shorter) Small transverse emittances

4. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 4 Forming the ion beam Main issues: Initial cooling time Bunch charge & spacing General recommendations: Prevent the emittance increase at beam transport (introducing a fast feedback) Use staged cooling Start cooling at possibly lowest energy Use the continuous cooling during acceleration in collider ring, if necessary Beam bunching, cooling and ramp agenda: After stacking in collider ring, the beam under cooling can be re-bunched by high frequency SC resonators, then re-injected for coalescence (if needed), more cooling and final acceleration & cooling The final focus could be switched on during the energy ramp, keeping the Q- values constant

5. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 5 Lifetime due to Intrabeam Scattering  IBS heating mechanism: Energy exchange at intra-beam collisions leads to x- emittance increase due to energy-orbit coupling, and y-emittance increase due to x-y coupling  Electron cooling is introduced to suppress beam blow up due to IBS, and maintain emittances near limits determined by beam-beam interaction.  Since L  1/  x  y, reduction of transverse coupling while conserving beam area, would result in decrease of impact of IBS on luminosity  Electron cooling then leads to a flat equilibrium with aspect ratio of 100:1.  Touschek effect: IBS at large momentum transfer (single scattering) drives particles out of the core, limiting luminosity lifetime.  A phenomenological model which includes single scattering and cooling time of the scattered particles has been used to estimate an optimum set of parameters for maximum luminosity, at a given luminosity lifetime.

6. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 6 High Energy Electron Cooling ERL based circulator electron cooler Initial cooling After bunching Colliding mode MomentumGeV/MeV12/6.660/33 Beam currentA0.6/3 Particle/bunch10 0.7/3.8 Bunch lengthmm 200/20 0 10/305/15 Energy spread10 -4 5/1 3/1 Hori. Emit. norm. mm410.56 Vert. emtt. norm.mm410.11 Laslett tune shift0.0020.0060.1 Cooling lengthm15 Cooling times921620.2 IBS growth time (longitudinal) s0.9 ERL/CR based staged EC in collider ring

7. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 7 Feasibility of High Energy Electron Cooling Beam adapters Allows one to flatten the e-beam area in order to reach the optimum cooling effect Advances on electron beam SRF energy recovering linac (ERL) Removes the linac power show-stopper Allows for two stages cooling or even cooling while accelerating Allows for fast varying the e-beam parameters and optics when optimizing the cooling in real time Delivers a low longitudinal emittance of e-beam Electron circulator-cooling ring Eases drastically the high current and energy exposition issues of electron source and ERL Beam transport with discontinuous solenoid Solves the problem of combining the magnetized beam transport (necessary for efficient EC) with effective acceleration

8. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 8 Beam-beam kicker for EC Kicker beam is not accelerated after the DC gun Both beams are flat in the kick section Flat beams can be obtained from magnetized sources (grid operated). Kicker beam is maintained in solenoid. It can be flatten by imposing constant quadrupole field Flat cooling beam is obtained applying round-to- flat beam adapters Circulating beam energyMeV33 Kicking beam energyMeV~0.3 Kicking frequencyMHz5 – 15 Kicking anglemrad0.2 Kicking bunch lengthcm15 – 50 Kicking bunch widthCm0.5 Kicking bunch chargenC2 Design parameters for beam-beam kicker A schematic of beam-beam fast kicker

9. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 9 Synchronization for EC Injector 5 MeVx25 mA ERL 75 MeV Fast kicker arc Fast kicker Cooling section Dumper 125 KWt i i

10. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 10 Short bunches make feasible the Crab Crossing SRF deflectors 1.5 GHz can be used to create a proper bunch tilt SRF dipole Final lens F F Crab Crossing Parasitic collisions are avoided without loss of luminosity R. Palmer 1988, general idea

11. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 11 Crab Crossing for EIC Short bunches also make feasible the Crab Crossing: SRF deflectors 1.5 GHz can be used to create a proper bunch tilt 22

12. Operated by the Southeastern Universities Research Association for the U.S. Department of Energy Thomas Jefferson National Accelerator Facility Page 12 Preliminary IP layout for ion beam CCB with inserted SRF for bunching and dispersive crabbing Dipoles bending the beam in addition to arcs Inserted SRF resonators are sufficient for required bunching and dispersive crabbing