Kinetic Effects in High Gain Free-Electron Lasers
Abstract
A formalism based on the Vlasov-Maxwell system has been developed that provides a fully kinetic description of a free-electron laser (FEL) operating in the high gain regime. The analysis allows for guiding of the optical beam through the gain process and guiding of the electron beam by the weak focusing provided by realistic wiggler gradients. Thus, betatron oscillations and emittance are naturally included. Additionally, intrinsic energy spread as well as energy spread due to space charge effects is included. The analysis predicts a novel electron beam equilibrium flow in which the effect of wiggler gradients tends to cancel that due to space charge, leading to a flow with reduced axial velocity spread. Since the FEL mechanism is sensitive to the axial velocity spread on the beam, this special flow appears to be useful in enhancing FEL gain. This and other issues related to FEL operation are discussed in this paper. It is shown that the scaled thermal velocity S = v(th) /(V(b) - V(ph)) is a useful measure of beam quality in the context of FELs. Here, v(th) is the thermal velocity on the beam, v(b) is the beam velocity and v(ph) is the phase velocity of the ponderomotive wave. The scaled thermal velocity depends on beam emittance, energy spread and electron density and is a useful indicator of beam quality since it provides a measure of the thermal spread as observed in the phase velocity frame. Analogies between the high gain FEL and plasma two-stream instability are discussed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 24, 2002
- Accession Number
- ADP012512
Entities
People
- Bahman Hafizi
- C. W. Roberson
Organizations
- United States Naval Research Laboratory