Free electron lasers and high-energy electron cooling

Cooling intense high-energy hadron beams remains a major challenge in modern accelerator physics. Synchrotron radiation of such beams is too feeble to provide significant cooling: even in the Large Hadron Collider (LHC) with 7 TeV protons, the longitudinal damping time is about thirteen hours. Two cooling methods (or combination of them) - stochastic cooling (CS) based on broad-back RF feedback(s) and electron cooling (EC) driven by energy recovery linac (ERL) - are under development for cooling high energy hadron colliders. In this paper we focus on Coherent Electron Cooling (CEC), an unique technique which promising significantly better efficiency that the above-mentioned techniques, in a wide energy range. In the early 1980s, CEC was suggested as a possibility for using various microwave instabilities in an electron beam to enhance its interaction with hadrons (i.e., cooling them). The capabilities of present-day accelerator technology, ERLs, and high-gain Free-Electron Lasers (FELs), finally caught up with the idea and provided the all necessary ingredients for realizing such a process at energies typical for hadron colliders. In this paper, we discuss the principles, and the main limitations of the CEC process based on a high-gain FEL driven by an ERL. We also present, and summarize in Table 1, some numerical examples of CEC for ions and protons in RHIC and the LHC.