O ct 1 99 6 NSF – ITP – 96 – 142 SLAC - PUB - 7337 October 1996 Laser cooling

A novel method of electron beam cooling is considered which can be used for linear colliders. The electron beam is cooled during collision with focused powerful laser pulse. With reasonable laser parameters (laser flash energy about 10 J) one can decrease transverse beam emittances by a factor about 10 per one stage. The ultimate transverse emittances are much below of that given by other methods. Depolarization of a beam during the cooling is about 5–15 % for one stage. This method is especially useful for photon colliders and open new possibilities for ee colliders and x-ray FEL based on high energy linacs. It is well known that due to the synchrotron radiation problem in ee storage rings the energy region beyond LEP-II can only be explored by a linear collider (LC). Such colliders for the center–of–mass energy 0.5–2 TeV are developed now in the main accelerator centers[1]. Beside ee collision at linear colliders one can ’convert’ electron to high energy photon using Compton backscattering of laser light and to obtain γγ and γe collisions with energies and luminosities close to that in ee collisions[2]-[7]. This possibility is included now in projects of the linear colliders. To obtain high luminosity, beams in linear colliders should be very tiny. At the interaction point (IP) in the current LC designs, beams with transverse sizes as low as σx/σy ∼ 200/4 nm are planned. Beams for ee collisions should be flat in order to reduce beamstrahlung energy losses during beam collision. For γγ collision beamstrahlung radiation is absent and to obtain high luminosity one can use beams with smaller σx [5, 6]. ∗Talk at the Int.Symposium New Modes of Particle Acceleration Techniques & Sources, ITP, UCSB, Santa Barbara, August 19–23, 1996