Electron drift instability in storage rings with electron cooling

Transverse drift mobility of the cooling electrons allows them to respond to the transverse offset of the cooled beam. This electron dipole feedback introduces imaginary parts in transverse collective modes of the cooled beam. The sign of these imaginary parts is found to be dependent on the charge sign of the cooled particles, giving a coherent damping for protons and instability for antiprotons. A coupling between the transverse degrees of freedom of the stored cooled beam changes the result, causing an instability for any sign of the charge. For typical low-energy cooler parameters, these growth/damping times are found to be in the region 0.1–10 s.