Publications

In this paper the concept of a stochastic electron beam is introduced. A stochastic electron beam is one for which the transverse dynamics is chaotic. Utilizing adiabatic orbits, the resonance overlap condition for transition to stochasticity in a particular electron beam system, the "triple-Bennett configuration," is derived. The tangent map is derived and used to state conditions for strong orbit instability and the resulting exponential decay of phase correlations. The dependence of the K entropy on the strength ε of the nonaxisymmetry of the triple-Bennett configuration is investigated numerically. Implications for the suppression of the ion-hose instability in the ion-focused regime are briefly discussed. © 1990 American Institute of Physics.

The ion-hose instability can catastrophically disrupt a classical electron beam propagating in the ion-focussed regime (IFR). Ion hose is driven by a resonant interaction between the smooth electron-betatron and ion-betatron orbits. In a classical beam phase correlations decay secularly in time c(t)/c(t{sub 0}) {approximately} (t{sub 0}/t){sup n} (0 < n {le} 2). In a stochastic electron beam the electron orbits are chaotic. Such a beam can be immune to resonant instabilities because phase correlations decay exponentially fast c(t)/c(0) {approximately} e{sup {minus}ht} thus destroying the coherence of the electron response on the growth time 1/{gamma}{sub g} if h {approximately} {gamma}{sub g}. Using the same principles we can also envision a stochastic damping cell in which electron phase correlations damp exponentially c(z)/c(0) {approximately} e{sup {minus}hz} thus centering and conditioning a beam more effectively than a classical phase-mixing cell in which c(z)/c(z{sub 0}) {approximately} (z{sub 0}/z){sup n}. A triple-Bennett'' IFR system and the analogous triple-wire'' damping cell are analyzed. The K-entrophy is introduced as a figure-of-merit for such stochastic electron beam systems. 16 refs., 7 figs.