High-Current ERL-Based Electron Cooling System for RHIC

Abstract

The design of an electron cooler must take into account both electron beam dynamics issues as well as the electron cooling physics. Research towards high‐energy electron cooling of RHIC is in its 3rd year at Brookhaven National Laboratory. The luminosity upgrade of RHIC calls for electron cooling of various stored ion beams, such as 100 GeV/A gold ions at collision energies. The necessary electron energy of 54 MeV is clearly out of reach for DC accelerator system of any kind. The high energy also necessitates a bunched beam, with a high electron bunch charge, low emittance and small energy spread. The Collider‐Accelerator Department adopted the Energy Recovery Linac (ERL) for generating the high‐current, high‐energy and high‐quality electron beam. The RHIC electron cooler ERL will use four Superconducting RF (SRF) 5‐cell cavities, designed to operate at ampere‐class average currents with high bunch charges. The electron source will be a superconducting, 705.75 MHz laser‐photocathode RF gun, followed up by a superconducting Energy Recovery Linac (ERL). An R&D ERL is under construction to demonstrate the ERL at the unprecedented average current of 0.5 amperes. Beam dynamics performance and luminosity enhancement are described for the case of magnetized and non‐magnetized electron cooling of RHIC.