Accurate setting of electron energy for demonstration of first hadron beam cooling with rf-accelerated electron bunches

Abstract

The world’s first electron cooling based on the rf acceleration of electron bunches was experimentally demonstrated at the Low Energy RHIC Electron Cooler (LEReC) at Brookhaven National Laboratory. The critical step in obtaining cooling of the Au ions in the collider with this new approach was matching the electron and ion relativistic γ-factors with a relative error of less than 5×10^{-4}. Since the electron beam kinetic energy was just 1.6 MeV, it was required to set the absolute energy of electrons with an accuracy better than 0.8 keV. The method of setting electron energy in conventional coolers was unsuitable for LEReC and a new technique had to be developed. In this paper we describe our experience with measuring the electron beam energy at LEReC and precisely matching electron and ion γ-factors, which resulted in demonstration of the cooling.