Relativistic description of electron Bernstein waves

Abstract

The application of the extraordinary and ordinary electron cyclotron waves for heating and current drive in overdense, magnetized plasmas is restricted. For frequencies near low harmonics of the electron cyclotron frequency these waves are cutoff near the edge of the plasma. For higher frequencies the interaction of the waves with electrons is weak leading to very low absorption of wave power. However, electron Bernstein waves provide means for heating and current drive in overdense plasmas since they have no density cutoffs and are strongly damped near harmonics of the electron cyclotron resonance. This paper discusses properties of electron Bernstein waves that make them an attractive means for delivering energy and momentum to electrons. An approximate analytical model for electrostatic waves in the weakly relativistic and weak damping limits is developed. From this model the propagation and damping characteristics of electron Bernstein waves and their dependence on plasma parameters are derived. It is found that relativistic effects are necessary to properly describe the resonant interaction of electron Bernstein waves with electrons. The characteristics of electron Bernstein wave propagation and damping are very different depending on whether the electron cyclotron harmonic resonance is approached from the low-or the high-field side. The results from the analytical model and the associated analysis agree well with the results from the exact numerical calculations. This validates the physics of the simplifying assumptions on which the model is based. The electron Bernstein waves are completely damped well before the electron cyclotron resonance due to the Doppler shift. Within the damping region the waves interact with suprathermal electrons thereby having the potential for efficient current drive.

Ebw Physics of Ece in NSTX

“…• The weakly-relativistic model of Decker & Ram [8] somewhat overestimates both LFS and HFS damping. However, the error is reasonable considering the simplicity of this model.…”

“…However, EC waves, and particularly EBWs, can change their propagation and absorption characteristics compared to the typical electron temperatures of present day experiments. Decker and Ram [8] show that at higher temperatures, EBWs become electromagnetically polarized, as opposed to their typical quasi-electrostatic polarization at lower temperatures. Even the propagation properties can be influenced by relativistic effects, as shown by Nelson-Melby et al [28].…”

“…Except for the non-relativistic damping term, we implemented and compared the weakly relativistic damping model of Decker & Ram [8], the weakly-relativistic model due to Saveliev [9] and a routine that integrates numerically the fully-relativistic dispersion tensor in the momentum space along the resonance curve [10]. The relative computational times are compared in Figure 1.…”

Quasilinear theory of electron transport by radio frequency waves and nonaxisymmetric perturbations in toroidal plasmas

“…Furthermore, for EC waves, the description has to be relativistic so that the damping of the waves and their interaction with electrons are described correctly [4][5][6][7]. In this paper, for an axisymmetric toroidal equilibrium, we derive a relativistic diffusion operator for the interaction of RF waves with electrons in the presence of non-axisymmetric magnetic field perturbations.…”

Dispersion relations for Bernstein waves in a relativistic pair plasma

“…These waves can propagate undamped only very close to the plane perpendicular to the static magnetic field. Such waves are of great interest since, in an electron-ion plasma, they strongly interact with the electrons and are excellent candidates for plasma heating and driving currents as compared with the electromagnetic (O)rdinary and the e(X)traordinary modes [7].…”