Free-electron laser sideband instability reconsidered. Interim report

Technical Report · Wed Aug 12 04:00:00 EDT 1987

OSTI ID:5814415

Riyopoulos, S; Tang, C M

The problem of sideband growth in a free-electron laser (FEL) is studied using canonical formalism. The exact unperturbed orbits, without sidebands, are obtained in action-angle variables for all particles. Integration of the linearized Vlasov equation with perturbing sidebands over the unperturbed orbits yields the sideband growth for both trapped and untrapped particles. The unperturbed distribution f sub o is in an 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 growth between upper and lower sidebands. The stability is determined by the sign of df sub o/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 o/dJ localized near the separatrix have the minimum growth rates. The structure and scaling of the unstable spectrum are different from previous results obtained for electrons localized at the bottom of the ponderomotive well.

• Research Organization: Naval Research Lab., Washington, DC (USA)
• OSTI ID: 5814415
• Report Number(s): AD-A-184269/9/XAB; NRL-MR-6028
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
420300* -- Engineering-- Lasers-- (-1989)
ELECTRICAL EQUIPMENT
ELECTROMAGNETS
EMISSION SPECTRA
EQUIPMENT
FREE ELECTRON LASERS
LASERS
MAGNETS
MECHANICAL PROPERTIES
PERTURBATION THEORY
SHEAR PROPERTIES
SPECTRA
WIGGLER MAGNETS