Ion-ripple laser as an advanced coherent radiation source

摘要

Abstract: We describe the Ion-Ripple Laser as an advanced schemefor generating coherent radiation. A relativisticelectron beam obligately propagating through an ionripple excites electromagnetic radiation which iscoupled to slow electrostatic waves with peak growthrate at the resonance frequency approximately egaapproximately 2$lambda$+2$/$-O$/k$-w$/c via backwardRaman scattering. This new scheme may provide noveltunable sources of coherent high-power radiation. Byproper choice of device parameters, sources ofmicrowaves, optical, and perhaps even x rays can bemade. By employing fluid theory the dispersion relationfor wave coupling is derived and used to calculate theradiation frequency and linear growth rate. Thenonlinear saturation mechanism is due to trapping ofthe beam electrons by the ponderomotive potential. Foran energetic electron beam, the peak growth rate isapproximately ega$-i$/ $EQ approximately ega$+5/2$/$-pe$/ $epsilon$-i$/ sin $theta@/$lambda$-O$/$+3/4$/(2k$- approximately ega$/c)$+3/2$/ and the efficiencyis $eta $EQ approximately ega$-pe$//(2k$- approximatelyega$/c$lambda$-O$/$+3/2$/). A 1 2/2 D-PIC simulationcode was developed to verify the ideas, scaling laws,and nonlinear mechanism. From the observed powerspectrum, backward Raman scattering is show to beresponsible for the radiation. The growth rates andefficiencies given by the simulation match the ones oftheory for different wiggler wave lengths and beam$lambda@. Both of them show a slow decrease withmomentum spread. Momentum spread also broadens theradiation spectrum.!25