Influence of untrapped electrons on the sideband instability in a helical wiggler free electron laser
The detailed influence of an untrapped-electron population on the sideband instability in a helical wiggler free electron laser is investigated for small-amplitude perturbations about a constant-amplitude (a-italic-circumflex/sup 0//sub s/ = const) primary electromagnetic wave with slowly varying equilibrium phase delta/sup 0//sub s/. A simple model is adopted in which all of the trapped electrons are deeply trapped, and the equilibrium motion of the untrapped electrons (assumed monoenergetic) is only weakly modulated by the ponderomotive potential. The theoretical model is based on the single-particle orbit equations together with Maxwell's equations and appropriate statistical averages. Moreover, the stability analysis is carried out in the ponderomotive frame, which leads to a substantial simplification in deriving the dispersion relation. Detailed stability properties are investigated over a wide range of dimensionless pump strength ..cap omega../sub B/ /GAMMA/sub b/ ck/sub 0/ and fraction of untrapped electrons f/sub u/ = n-italic-circumflex/sub u/ /n-italic-circumflex/sub b/. When both trapped and untrapped electrons) are present, there are generally two types of unstable modes, referred to as the sideband mode, and the untrapped-electron mode. For f/sub u/ = 0, only the sideband instability is present.
- Research Organization:
- Science Applications International Corporation, Boulder, Colorado 80302
- OSTI ID:
- 6288584
- Journal Information:
- Phys. Fluids; (United States), Journal Name: Phys. Fluids; (United States) Vol. 30:9; ISSN PFLDA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
420300* -- Engineering-- Lasers-- (-1989)
ELECTRICAL EQUIPMENT
ELECTROMAGNETS
ELECTRON DENSITY
ELECTRONS
ELEMENTARY PARTICLES
EQUILIBRIUM
EQUIPMENT
FERMIONS
FREE ELECTRON LASERS
HELICITY
INSTABILITY
LASERS
LEPTONS
MAGNETS
MATHEMATICAL MODELS
OSCILLATION MODES
PARTICLE PROPERTIES
RADIATION SOURCES
TRAPS
WIGGLER MAGNETS