Fast wave damping on non-Maxwellian electrons

Theoretical studies of fast wave damping on electrons are presented. Different regimes of importance for fast wave plasma heating and current drive in tokamaks are considered. Various cases of Maxwellian and multi-Maxwellian, isotropic and anisotropic electron distribution functions are investigated. In all cases, fast wave damping on electrons is due to three terms: Landau damping, transit-time magnetic pumping (TTMP), and the cross-term effect. Expressions for all these terms are derived for all regimes considered. Although in most cases Landau damping, TTMP, and the cross-term effect are the same order of magnitude, regimes are found that can be referred to as the pure Landau damping regimes, or pure TTMP regimes. A key parameter that defines the character of fast wave damping is found: δ_α=ε₂/ γ_αεε₃. In simplified form, and far from resonances, it can be written as δ_α≈- 2ω²/Ω_iΩ_eβ _α, where α specifies the appropriate regime.