  The paper considers methods of particle cooling mostly concentrating on
cooling of high energy heavy particles in the high energy colliders. Presently,
there are two major methods of the cooling the electron cooling and stochastic
cooling. The latter can be additionally separated on the microwave stochastic
cooling, the optical stochastic cooling (OSC) and the coherent electron cooling
(CEC). OSC and CEC are essentially extensions of microwave stochastic cooling
operating in 1-10 GHz frequency range to the optical frequencies corresponding
to 30-300 THz frequency range. The OSC uses undulators as a pickup and a
kicker, and an optical amplifier for signal amplification, while the CEC uses
an electron beam for all these functions.
