Concept of entropy in the realm of charged particle beams

Abstract

Stochastic phenomena occurring within charged particle beams can be handled using the Vlasov-Fokker-Planck generalization of the Vlasov equation. In particular, this non-deterministic approach can deal with effects due to Coulomb scattering between the beam particles. Moreover, stochastic phenomena also occur in computer simulations of charged particle beams. Both processes -- although different in their physical nature -- can be described by the Vlasov-Fokker-Planck equation, as in both cases the underlying stochastic process can be classified as a Markov process. This description is applied to beams in periodic focusing systems. We derive an equation relating the change of the $\mu$-phase space entropy to the change of rms-emittance and ``temperature weighted excess field energy''. This equation enables us both to improve our capability to interpret the results of computer simulations, as well as to identify the conditions needed to minimize scattering induced degradation of the quality of beams circulating in storage rings.