Twoenergy Storage Ring Cooler Status Report Fanglei Lin

Two-energy Storage Ring Cooler --- Status Report Fanglei Lin on behalf of Bhawin Dhital, Slava Derbenev, Geoff Krafft, Vasiliy Morozov, Yuhong Zhang JLEIC R&D Meeting, June 27 th, 2019

Motivation • Cooling of ion beams to reduce the beam emittance and compensate the IBS emittance degradation is crucial to deliver high luminosity and extend luminosity lifetime in a collider in low or medium ion energy ranges (a few to a few hundred Ge. V). • ERL-based circulator ring is proposed to boost the electron beam and recover the large beam power, and reduce the average current from the cathode. But it required magnetized beam gun, injector and a fast kicker, which are still challenging. • We propose a storage cooler ring, where the electron beam is stacked and circulates. So no challenge on the lifetime of the source and a fast kicker. High cooling beam quality can be obtained through naturally-occurring synchrotron damping counteracting the heat of electron beam by the intra- and inter- beam scattering. JLEIC R&D Meeting, June 27 th, 2019 2

History • The concept was first considered by Budker. • Two groups (Derbenev&Skrinsky and D. Clines et al) re-investigated in 70 s －Proposed electron cooling for HERA and RHIC by Derbenev et al. in late 90 s (Nuc. Inst. and Meth. Phys. Res. A 424(1999)277 -295, FERMILAB-TM-2058). • Extensive discussion among S. Derbenev, D. Douglas, G. Krafft, R. Li and Y. Zhang in 2013 (mentioned in Yuhong’s slides in 2015). • Y. Zhang revisited the storage ring cooler concept in 2015 and suggested to use damping wiggler to enhance the SR damping with an energy jump (4 presentations between July and August 2015). • J. Guo and V. Morozov suggested a figure-8 design with an ERL loop. • F. Lin and V. Morozov completed an initial technical approach and designed a preliminary optics in 2015. JLEIC R&D Meeting, June 27 th, 2019 3

Design Parameters and Work Plan in FOA Proposal Year I: Parameter Unit Energy Me. V 20 -55 Current A 0. 5 -1 Repetition rate MHz 476 rms bunch length cm 3 Normalized emittance* m-rad 100 -500 Energy spread 10 -4 1 Solenoid field T 2 Solenoid length m 20 -30 JLEIC R&D Meeting, June 27 th, 2019 • Improvement of prototype linear optics of a storage-ring electron cooler, including properly including aspects of creating magnetized beam for the electron cooling section • Optimization of cooler parameters • Analytic estimation of intra-and-inter beam scattering and space charge effects Year II: • Estimation of equilibrium emittances • Initial single-particle tracking • Analysis of HOM impedance requirements for the SRF structure • Identify potential issues such as coherent synchrotron radiation and beam break up • Publish Journal paper on Recirculated Linac Coolers 4

Proposed Storage Ring Cooler • Technical approach (October 2015) chirp 3 cm, 3 e-4 Full energy injection 3 cm, 1 e-4 Flat to round beam transform 3 cm, 1 e-4 Cooling solenoid (i) (ii) compression arc dechirp decompression arc Round to flat beam transform 55 Me. V cooling ring (round beam) 1 cm, 3 e-4 (ix) Energy recovering SRF (viii) 1 cm, 3 e-4 (x) (xi) (iii) (vii) 3 cm, 3 e-4 1 cm, 1 e-4 dechirp (iv) (v) 1 cm, 1 e-4 1 cm, 3 e-4 155 Me. V damping ring (flat beam) decompression arc JLEIC R&D Meeting, June 27 th, 2019 Wigglers chirp 0. 3 cm, 3 e-4 (vi) compression arc 5

Current Status • Established design and simulation environments in codes MADX and Elegant. • Verified the longitudinal stability with accelerating and deaccelerating cavities in the two energy storage ring cooler. Analytical calculation and numerical simulation show stable solutions existing for both ”Storage Ring” (SR) mode and “Energy Recovery Linac” (ERL) mode (SR mode resembles the usual sing storage ring with strong synchrotron motion and ERL mode is the case where RF in two beam passes nearly cancels). The longitudinal acceptance of two-energy ring is large. • Understood momentum compaction, chirping and dechirping. Established chirping and dechirping simulations properly. • Exploring mechanisms to reach the desired bunch length and energy spread. • Initiating front-to-end numerical simulations for the longitudinal motion, including chirping, dechirping, accelerating and deaccelerating cavities in the two energy storage ring cooler. JLEIC R&D Meeting, June 27 th, 2019 6