R. L. Meyer

Wave absorption near the electron cyclotron frequency

Wave absorption for frequencies near the electron cyclotron frequency for the ordinary and extraordinary modes is investigated. The role of finite electron Larmor radius effects is discussed. A numerical analysis of the relevant dispersion relation in the weakly relativistic and nonrelativistic limit is presented. The density dependence (1/ne) of the damping of the extraordinary wave for not too small densities and the strong absorption of the ordinary wave for quasi‐perpendicular propagation in a hot plasma (Te≳1 keV) are investigated numerically for several angles of incidence.

Role of the relativistic mass variation in electron cyclotron resonance wave absorption for oblique propagation

The role of the relativistic mass variation on wave absorption in the electron cyclotron range of frequencies is investigated. It is first shown that the validity of the nonrelastivistic linear dispersion relation for a Maxwellian plasma is restricted by the conditions N2∥≫Te/mc2 and N2∥≫‖1−ω2c/ω2‖. A numerical investigation of wave damping in a plasma slab located in an inhomogeneous tokamak‐like magnetic field shows that for most angles of practical interest the latter condition is easily violated and, therefore, the nonrelativistic dispersion relation yields inaccurate results. The problem of the validity of the nonrelativistic quasilinear equation for oblique propagation is also discussed. Using a quasilinear model equation, it is shown that the inclusion of the relativistic mass variation in the diffusion coefficient results in a basic change of the wave–particle selective interaction compared to the nonrelativistic approximation for any value of Te or N∥.

Electron cyclotron emission from tokamak plasmas with mildly superthermal electrons

The emission of cyclotron radiation from a tokamak plasma in the presence of a high toroidal current is investigated. For the fundamental frequency, a theory of the radiation which consistently includes the hot plasma polarization effects is developed. The high current density electron system is described by a distribution function which is the sum of two Maxwellian functions representing the body of the electron population and a small fraction of superthermal drifting electrons, respectively. The emission of the ordinary and extraordinary modes in the equatorial plane of the torus for quasi‐perpendicular propagation is investigated numerically. It is found that the radiation temperature deduced from the emission of radiation on the high Bt side of the torus differs from that on the low Bt side, where Bt is the confining magnetic field.

Current drive by the combined effects of electron-cyclotron and Landau wave damping in tokamak plasmas

The theory of current drive by the combined effects of lower‐hybrid and electron‐cyclotron wave absorption is investigated. The case of a spatially homogeneous lower‐hybrid diffusion coefficient and the electron ordinary mode propagating nearly normal to the magnetic field is considered. The effect of selective electron‐cyclotron wave absorption for optimizing lower‐hybrid current drive is discussed for two situations, namely, the wave frequency close to or much less than the electron‐cyclotron gyrofrequency, which corresponds to particle heating for moderate velocities and mildly relativistic energies, respectively. In the former case, by using the numerical solution of the Fokker–Planck equation it is shown that electron heating is suited for controlling the density of the current‐carrying tail. The latter case is investigated for moderate wave powers and is shown to be most appropriate for optimizing the ratio J/P.

Electron cyclotron emission in a rf current‐driven tokamak plasma

The general properties of electron cyclotron radiation emitted by the current‐carrying superthermal tail in tokamak plasmas are investigated. Two situations are considered, namely, the case of an extended tail as it occurs in present‐day experiments and that in which the velocity range of the tail is much less than its mean speed. For the former case, we show that most of the emitted radiation obeys Kirchhoff’s law. In the latter case, which is suited for reactor‐like parameters, a simple relation is obtained between the tail momentum distribution and the radiation temperature.

Electron cyclotron heating in rf current‐driven tokamak plasmas

Wave absorption near the electron cyclotron gyrofrequency by the current‐carrying energetic tail in tokamak plasmas is investigated. It is shown that by the proper choice of the angle of propagation, strong wave damping occurs for wave frequencies much less than the central electron cyclotron frequency and that the extraordinary mode can be launched from the low magnetic field side of the torus. It is also found that wave absorption is weakly dependent on the perpendicular temperature of the resonant particles.

Power dependence of electron cyclotron wave damping in tokamak plasmas

The power dependence of the wave damping in a tokamak plasma for arbitrary direction of propagation, mode of polarization, and wave frequency is investigated. Using a 2‐D Fokker–Planck code, it is shown that the wave damping increases or decreases with the rf power depending on the velocity range of the absorbing electrons.

Fokker-Planck code for the quasi-linear absorption of electron cyclotron waves in a tokamak plasma

Abstract We present the solution of the kinetic equation describing the quasi-linear evolution of the electron momentum distribution function under the influence of the electron cyclotron wave absorption, Coulomb collisions and the dc electric field in a tokamak plasma. The solution of the quasi-linear equation is obtained numerically using a two-dimensional initial value code following an ADI scheme. Most emphasis is given to the full non-linear and self-consistent problem, namely, the wave amplitude is evaluated at any instant and any point in space according to the actual damping. This is necessary since wave damping is a very sensitive function of the slope of the local momentum distribution function because the resonance condition relates the electron momentum to the location of wave energy deposition.

Temperature dependence of synchrotron radiation loss in inhomogeneous tokamak plasmas

Synchrotron radiation in a tokamak with inhomogeneous plasma parameters is investigated to determine the role of the temperature profile on the global loss. Using reactor relevant parameters, it is shown that synchrotron radiation is profile dependent, namely, at constant thermal energy, the emitted radiation increases with the peak temperature. An approximated analytical formula for the global loss is found.

Structure of electron-cyclotron ordinary mode damping

The ordinary mode damping near the electron‐cyclotron frequency is investigated using the relativistic dispersion relation. It is shown that the Doppler splitting of the absorption spectrum claimed by Arunasalam et al. [Phys. Rev. A 36, 3909 (1987); 37, 2063 (1988)] is an erroneous result obtained from an oversimplified dispersion relation and assuming an infinite speed of light in the resonance condition.