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MEIC Electron Cooler Design Concept

MEIC Electron Cooler Design Concept. EC potential impact to colliders. Reaching a high start luminosity

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MEIC Electron Cooler Design Concept

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  1. MEIC Electron Cooler Design Concept

  2. EC potential impact to colliders Reaching a high start luminosity • Very short i-bunches achieved by longitudinal cooling in combination with SRF(cannot be attained with stochastic cooling!) make sense to design a super-strong focusing (low beta) at IP • Short bunches allow one toemploythe crab-crossing beams, thus avoiding the parasitic b-binteractions • Low transverse emittance + high rep. rate allow one to minimize charge/bunch Extending the luminosity lifetime • ECsuppresses beam heating and luminosity loss caused by multiple and Touschek IBS

  3. HEEC basics solenoid Co-moving “cold” electron beam serves as thermostat for a hot ion beam (i – e Coulomb collision exchange) ion bunch electron bunch Cooling section Magnetized e-gun Injector SRF linac Cooling conditions: Cooling time grows with Therefore: staged cooling

  4. Staged EC Initial electron cooling High luminosity colliding beams * norm. rms • ** max. amplitude * norm. rms

  5. Staged Cooling in Ion Collider Ring • Initial cooling after ions injected into the collider ring for reduction of 3d emittance before acceleration • After boost & re-bunching, cooling for reaching design values of beam parameters in colliding mode • Continuous cooling during collision for suppressing IBS, maintaining luminosity lifetime

  6. High Energy e-Cooler for Collider Ring • Design Requirements: • up to 10.8 MeV for cooling at injection energy (20 GeV/c) • up to 54 MeVfor cooling top proton energy (100 GeV/c) • Cooling e-beam current : • up to 1.5 A CW beam at 750 MHz repetition rate • About 2 nC bunch charge (possible space charge issue at low energy) • Solution: ERL Based Circulator Cooler (ERL-CCR) • Must be an SRF Linacfor accelerating electron beam • Must be Energy Recovery (ERL) to solve RF power problem • Must be Circulator -cooler ring (CCR) for reducing current from source/ERL • ERL-CCR is considered to provide • the required high cooling current while consuming • fairly low RF power and • reasonable current from injector

  7. Conceptual Design of Circulator e-Cooler (Layout A) solenoid ion bunch electron bunch Electron circulator ring Cooling section Fast beam kicker Fast beam kicker energy recovery path SRF Linac electron injector dump

  8. ERL Circulator Electron Cooler (Layout B) solenoid ion bunch electron bunch Cooling section (Fast) kicker (Fast) kicker dump injector SRF Linac

  9. Optimized Location of Cooling Channel (Layout C) 10 m Solenoid (7.5 m) injector SRF Center of Figure-8 dumper • Eliminating a long circulating beam-line could • cut cooling time by half, or • reduce the cooling electron current by half, or

  10. Cooler Design Parameters • Number of turns in circulator cooler ring is determined by degradation of electron beam quality caused by inter/intra beam heating up and space charge effect. • Space charge effect could be a leading issue when electron beam energy is low. • It is estimated that beam quality (as well as cooling efficiency) is still good enough after 100 to 300 turns in circulator ring. • This leads directly to a 100 to 300 times saving of electron currents from the source/injector and ERL.

  11. Issues Space charge limitations in CCR: • Coulomb interaction (non-linear Laslett detune) • CSR Intra- and Inter-Beam Scattering in CCR Source/Injector/ERL/CCR beam matching gymnastics • Magnetized cathode • Matching with cooling solenoids, straights and arcs • Beam size at cathode and related canonical emittance • Other agendas? (space charge dominated beam in axial optics…) Fast kicker (beam-beam or other) And more…

  12. Backup slides

  13. ERL-based EC with circulator ring

  14. Technology: Ultra-Fast Kicker Beam-beam kicker V. Shiltsev, NIM 1996 F • A short (1~ 3 cm) target electron bunch passes through a long (15 ~ 50 cm) low-energy flat bunch at a very close distance, receiving a transverse kick • The kicking force is • integrating it over whole kicking bunching gives the total transverse momentum kick • Proof-of-principle test of this fast kicker idea can be planned. Simulation studies will be initiated. surface charge density v≈c h D kicking beam σc v0 L An ultra-fast RF kicker is also under development.

  15. Estimates for Injector to ERL Electron source e-gun V 500 KeV Pulse duration 0.33 ns Bunch charge 2 nC Peak current 0.65 A Emittance, norm 1 mm.mrad Rep.rate15 MHz Averagecurrent30 mA 1st compressor • Prebuncher frequency 500 MHz • Voltage 0.2 MV • Energy gradient after prebuncher2x 10% 1st drift 2 m Bunch length after 1st compression 1 cm Beam radius (assumed value) 2 mm Coulomb defocusing length 30 cm 1staccellerator cavity Voltage 2 MV Frequency 500 MHz Beam energy 2.5 MeV 2nd compressor Buncher frequency 1.5 GHz Energy gradient 2 x 10% 2nd drift 1.8 m Bunch length, final 0.5mm Beam radius 2 mm Coulomb defocusing length 35 cm

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