Bernstein waves are electrostatic waves, which are efficiently absorbed at the electron-cyclotron resonance. They can be used to heat over-dense plasmas and are created in a so-called O-X-B mode conversion process. The conversion efficiency depends on the angle between wave vector and magnetic field at O-mode cutoff. To investigate the O-X-B conversion process an antenna with a steerable characteristic has been built
A detailed simulation of the O-X-B conversion process was done with IPF-FDMC full-wave code. The figure shows the positive value of the wave electric field when the wave enters the plasma under an optimum angle in O-mode. The density gradient is parallel to the y axis, the magnetic field parallel to the x axis. At a region around the O-mode cutoff the O-X conversion occurs. The direction of propagation of the X-mode is indicated by the grey arrow. The X-B conversion happens at the upper-hybrid resonance and a backwards propagating Bernstein wave is generated. Its direction of propagation is indicated by the light grey arrow. The formation of the Bernstein wave takes several hundred wave periods.
The array antenna is currently used for the investigation of O-X-B conversion in TJ-K.
Research associate, Plasma Dynamics and Diagnostics