Redirection of radio-frequency power flow by filaments

When radio-frequency waves propagate through magnetized plasmas, they scatter at density filaments, which are usually aligned with the magnetic field lines. We show that this scattering can redirect part of the power from the perpendicular direction to the parallel direction (along the field lines, along the filament). In magnetic confinement fusion devices, such as tokamaks, plasma is often heated by ion cyclotron range of frequency (ICRF) antennas. For such antennas, our simulations show that a parallel Poynting flux in the level of 1 MW m−2 can be generated by this power redirection mechanism. The increase of the magnitude of electric and magnetic fields of the wave in the filament is responsible for the parallel redirection of power flow. Simulations with constant density in the filament and background plasma show that the dominant parallel wavenumbers of the energy spectrum in the filament are increased and additional wavenumbers can be generated. In the cases with an experimental density profile, only the energy spectrum inside the filament is significantly affected while the rest remains almost the same.