MEIC Electron Cooling Simulation

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

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 1034 cm-2s-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 YaroslavDerbenev Talk on Tuesday MEIC ion complex He Zhang

DC and ERL-Circulator Cooler for MEIC Cooling section • 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 ion bunch electron bunch solenoid Fast kicker Fast kicker circulator ring • 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) dump SRF Linac injector YaroslavDerbenev 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 He Zhang

Step 1: Cooling in Pre-Booster (3 GeV) He Zhang

Step 2: Cooling in Collider Ring (25 GeV) 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

Cooling at High Energy w/ Existing Technologies ion bunch solenoid “Weak” ERL Cooler • Only for heavy ions • Bandwidth: 4~9 GHz • Lead ions: 5.1x107 per bunch • Bunch length: 2 cm effective ions in the ring: 1.37x1012 • Cooling time: ~ 14 min Bunched Stochastic Cooling electron bunch Cooling section RHIC Fast kicker circulator ring Fast kicker • No circulating ring (no fast kicker) • Electron current: ~ 100 mA • Electron bunch charge: 0.133 nC • Electron beam power: 2.75 to 5.5 MW • Needs ERL dump injector SRF Linac

With “Weak” Cooling in Collider Ring (25 GeV) • 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 3×109/bunch to reduce IBS • Luminosity is about 3×1033cm-2s-1 He Zhang

With “Weak” Cooling in Collider Ring (100 GeV) • At 100 GeV, reduce proton charge number to 3×109/bunch to reduce IBS • Luminosity is about He Zhang

Luminosity of Strong Cooling, Weak Cooling and No Cooling in Collider Ring • 100 GeV • 60 GeV • Nominal design: 6.5×1033cm-2s-1 • Weak cooling: 3×1033cm-2s-1 • No cooling: above 2×1033cm-2s-1 in two hours. • Nominal design: 5.4×1033cm-2s-1 • Weak cooling: 1.5×1033cm-2s-1 • No cooling: above 1.6×1033cm-2s-1 in two hours. He Zhang

Conclusions • Under ideal condition • In Pre-booster, KEp=3GeV, ε reduced from 1.75 μm to 0.8/0.55 μm. (Similar with the DC cooler in COSY) • In collider ring, KEp=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 1033 cm-2s-1 in two hours • A weak cooling (state of art) in the collider ring can keep the luminosity above 1033 cm-2s-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

He Zhang

MEIC Electron Cooling Simulation