MEIC Electron Cooling Simulation He Zhang 03/18/2014, EIC 14 Newport News, VA

He Zhang Outline Introduction MEIC Multi-phased Cooling Scheme MEIC Cooling Simulation Studies Case 1: Nominal Design (Three-Stage Cooling) Case 2: No Electron Cooling in the Collider Ring Case 3: With “Weak cooling” in the collider ring Conclusion and discussions

He Zhang Introduction The MEIC conceptual design aims for reaching ultra high luminosity up to cm -2 s -1 per interaction point The MEIC luminosity concept is based on high repetition rate crab- crossing colliding beams. This design concept relies on strong cooling of protons & ions Achieving small transverse emittance (small spot size at IP) Achieving short bunch (with strong SRF) Enabling ultra strong final focusing (low β*) and crab crossing Suppressing IBS, expanding high luminosity lifetime MEIC design adopts traditional electron cooling MEIC design adopts a multi-phase cooling scheme for high cooling efficiency We use computer simulations to validity the cooling design concept and beam parameters

He Zhang MEIC Three-Step Cooling Scheme Multi-phased scheme takes advantages of high electron cooling efficiency at low energy and/or small 6D emittance Step 1: Low energy DC cooling at the pre-booster Step 2: Bunched cooling at the ion injection energy (25 GeV) of the collider ring Step 3: Bunched cooling at the top ion energy (100 GeV) of the collider ring MEIC ion complex Yaroslav Derbenev Talk on Tuesday

He Zhang DC and ERL-Circulator Cooler for MEIC ion bunch electron bunch circulator ring Cooling section solenoid Fast kicker SRF Linac dump injector MEIC needs two electron coolers DC cooler (within state-of-art, a 2 MeV cooler is in commissioning at COSY) ERL circulator cooler need significant R&D High energy cooler – beyond state-of-the-art – there are significant challenges Cooling by a bunched electron beam Making and transport of high current/intensity magnetized electron beam Present design concept ERL + circulator ring To meet following challenges High RF power (up to 81 MW) High current ERL (up to 1.5 A) High current source (short lifetime) Yaroslav Derbenev Talk on Tuesday

He Zhang MEIC Cooling Simulation Assumptions for simulation Ion beam has Gaussian distribution. Electron beam is magnetized. Electron beam has uniform distribution in the DC cooler (pre- booster) and Gaussian distribution in the ERL circulator cooler (Collider ring). The shape and distribution of electron beam does NOT change during cooling. Misalignment is not considered. Cooler is modeled as thin lens. BETACOOL is used for the simulation.

He Zhang Simulation Parameters Key parameters for MEIC three-step cooling scheme Pre-BoosterCollider Ring Proton EnergyGeV32560/100 Proton Number2.52× × ×10 9 /bunch Proton Bunch LengthcmCoasting 1 Cooler TypeDCERL circulator Magnetic Field in CoolerT122 Cooler Lengthm102×30 Electron Beam CurrentA31.5 Electron Bunch Lengthcm11

He Zhang Step 1: Cooling in Pre-Booster (3 GeV) IBSECOOLIBS+ECOOL RHRH 1/s RVRV 1/s RLRL 1/s

He Zhang Step 2: Cooling in Collider Ring (25 GeV) IBSECOOLIBS+ECOOL RHRH 1/s RVRV 1/s3.47× RLRL 1/s

He Zhang Step 3: Cooling in Collider Ring (60 GeV) IBS no coupling IBSECOOLIBS+ECOOL RHRH 1/s RVRV 1/s RLRL 1/s

He Zhang Step 3: Cooling in Collider Ring (100 GeV) IBS no coupling IBSECOOLIBS+ECOOL RHRH 1/s RVRV 1/s4.99× RLRL 1/s

He Zhang No Cooling in The Collider Ring: Emittance Growth and Luminosity Decay Due to IBS The DC cooling in pre-booster (3 GeV) provides an initial emittance reduction to 0.8 and 0.55 mm mrad

He Zhang No Cooling in The Collider Ring: Emittance Growth and Luminosity Decay Due to IBS The DC cooling in pre-booster (3 GeV) provides an initial emittance reduction to 0.8 and 0.55 mm mrad

He Zhang No Cooling in The Collider Ring: Emittance Growth and Luminosity Decay Due to IBS The DC cooling in pre-booster (3 GeV) provides an initial emittance reduction to 0.8 and 0.55 mm mrad

He Zhang No Cooling in The Collider Ring: Emittance Growth and Luminosity Decay Due to IBS The DC cooling in pre-booster (3 GeV) provides an initial emittance reduction to 0.8 and 0.55 mm mrad

Cooling at High Energy w/ Existing Technologies Only for heavy ions Bandwidth: 4~9 GHz Lead ions: 5.1x10 7 per bunch Bunch length: 2 cm  effective ions in the ring: 1.37x10 12 Cooling time: ~ 14 min ion bunch electron bunch circulator ring Cooling section solenoid Fast kicker SRF Linac dump injector “Weak” ERL CoolerBunched Stochastic Cooling RHIC No circulating ring (no fast kicker) Electron current: ~ 100 mA Electron bunch charge: nC Electron beam power: 2.75 to 5.5 MW Needs ERL

He Zhang With “Weak” Cooling in Collider Ring (25 GeV) IBSECOOLIBS+ECOOL RHRH 1/s RVRV 1/s3.47× RLRL 1/s At 25 GeV, a “weak” cooling by 330 mA electron beam is strong enough to cool the coasting proton beam.

He Zhang With “Weak” Cooling in Collider Ring (60 GeV) At 60 GeV, reduce proton charge number to 3×10 9 /bunch to reduce IBS Luminosity is about 3×10 33 cm -2 s -1

He Zhang With “Weak” Cooling in Collider Ring (100 GeV) At 100 GeV, reduce proton charge number to 3×10 9 /bunch to reduce IBS Luminosity is about

He Zhang Luminosity of Strong Cooling, Weak Cooling and No Cooling in Collider Ring 60 GeV 100 GeV Nominal design: 6.5×10 33 cm -2 s -1 Weak cooling: 3×10 33 cm -2 s -1 No cooling: above 2×10 33 cm -2 s -1 in two hours. Nominal design: 5.4×10 33 cm -2 s -1 Weak cooling: 1.5×10 33 cm -2 s -1 No cooling: above 1.6×10 33 cm -2 s -1 in two hours.

He Zhang Conclusions Under ideal condition In Pre-booster, KE p =3GeV, ε reduced from 1.75 μm to 0.8/0.55 μm. (Similar with the DC cooler in COSY) In collider ring, KE p =25GeV, ERL circulator cooler, ε reduced to 0.3/0.25 μm. In collider ring, KEp=60~100GeV, ERL circulator cooler, maintain or further reduce ε. Design parameters of MEIC cooling system is achievable. Even without the cooling in the collider ring, the luminosity is above cm -2 s -1 in two hours A weak cooling (state of art) in the collider ring can keep the luminosity above cm -2 s -1

He Zhang Future Works Gaussian distribution of the ion beam is assumed during the cooling process, which is not necessarily true. Analytical formulas are used to calculate the friction force, and their accuracy in MEIC parameter range needs to be checked. How electron bunch distribution changes during the cooling process and the effects on cooling due to the changes need to be studied, since they are repeatedly used. More accurate models may need to be developed and applied.

He Zhang