Accession Number : ADA182153

Title :   The Free Electron Laser Sideband Instability Reconsidered,

Corporate Author : NAVAL RESEARCH LAB WASHINGTON DC

Personal Author(s) : Riyopoulos,S ; Tang,C M

PDF Url : ADA182153

Report Date : Jan 1986

Pagination or Media Count : 21

Abstract : The one-dimensional fast time averaged Hamiltonian is derived in a free electron laser (FEL) for electrons passing through a constant wiggler and a radiation field. The exact unperturbed orbits without sidebands are obtained for all particles and arbitrary separatrix width delta sub gamma. Integration in action-angle variables of the linearized Vlasov equation with perturbing sidebands over the unperturbed orbits yields the sideband gain for both trapped and untrapped particles. The unperturbed distribution f sub 0 is in an adiabatic equilibrium with the main signal field. It is found that upper and lower sidebands that are symmetric relative to the FEL frequency have opposite growth rates. There is no differentiation in the magnitude of the gain between upper and lower sidebands. The stability is determined by the sign of df sub 0/d omega sub b, i.e., the relative population of oscillation quanta h-bar omega sub b, omega sub b = bounce frequency around resonance. The shear d omega sub b/dJ, where J is the action variable, is stabilizing and distributions with gradients df sub 0/dJ localized near the separatrix have the minimum growth rates. The structures and scaling of the unstable spectrum are different from previous results obtained for electrons localized at the bottom of the ponderomotive well.

Descriptors :   *FREE ELECTRON LASERS, *ENERGY TRANSFER, *ELECTRON BEAMS, *MAGNETS, ADIABATIC CONDITIONS, EQUILIBRIUM(GENERAL), ELECTRONS, HAMILTONIAN FUNCTIONS, ONE DIMENSIONAL, QUICK REACTION, ORBITS, YIELD, PERTURBATIONS, PARTICLES, EQUATIONS, GROWTH(GENERAL), RATES, SIGNALS, RADIATION, POPULATION, SIDEBANDS, SPECTRA, WIDTH, GAIN, DISTRIBUTION, STABILIZATION, LOW FREQUENCY

Subject Categories : Lasers and Masers

Distribution Statement : APPROVED FOR PUBLIC RELEASE