Obtaining Transverse Cooling With Nonmagnetized Electron Beam

The first electron cooling with rf-accelerated electron bunches was recently demonstrated at the low energy RHIC electron cooler (LEReC) at BNL. Successful cooling requires that the electrons in the cooling section have a small angular spread and are well aligned with respect to the copropagating ions. LEReC puts into practice a nonmagnetized cooling of the ions at Lorentz factors of gamma = 4.1 and 4.9. Hence, unlike in previous coolers, in which the transverse electron dynamics is constrained by longitudinal solenoid fields, the ion-electron focusing and steering strongly contribute to the average angular spread of the electron beam. In this paper we discuss the factors that affect the electron angles and describe the process of tuning the electron beam to maximize the cooling of ion bunches in RHIC.