Upper hybrid wave pumped free electron laser

Abstract

A large amplitude upper hybrid wave has potential to be employed as a wiggler for the generation of high frequency coherent radiation via free electron laser (EEL) instability. At a density fluctuation level of a few percent, due to the upper hybrid wave, the growth time of FEL instability, with electron beam current of a few kilo ampere, turns out to be of the order of a nanosecond. The growth rate of FEL instability depends sensitively on ω1 and this dependence comes through νosc the beam oscillatory velocity. νosc acquires large values at k0z≃[ω0-(ωe/γ 00)]νb≃ωc [1-(1/γ00)]νb. At this value of k0z,ω≃2γ002ω c[2-(1/γ00)]. However, this scheme of FEL operation suffers from a severe limitation due to the parametric instability of the upper hybrid wave. The process of parametric decay into lower hybrid and upper hybrid waves may have growth rate comparable to that of the FEL instability