Radiation Reaction in a Continuous Focusing Channel

We show that the radiation damping rate of the transverse action of a particle in a straight, continuous focusing system is independent of the particle energy, and that no quantum excitation is induced. This absolute damping effect leads to the existence of a transverse ground state to which the particle inevitably decays and yields the minimum beam emittance that one can ever attain, γεₘᵢₙ0ex0ex=0ex0ex/2mc, limited only by the uncertainty principle. Because of adiabatic invariance, the particle can be accelerated along the focusing channel in its ground state without any radiation energy loss.