Theory of the anomalous Doppler instability during lower-hybrid current drive

An instability condition is derived for electrostatic waves obeying the dispersion relation ω = ω/sub pe/k/sub parallel//k using a two dimensional electron distribution function, f(v/sub parallel/,v/sub perpendicular/), appropriate for lower-hybrid current drive. It is found that when the raised plateau in f in the velocity range v1 < v/sub parallel/ < v2 has a sufficiently large anisotropy, T/sub p parallel/ > T/sub p perpendicular/, this mode can become unstable. If the plateau velocities satisfy the condition v2/v1 > 1 + ω/sub ce//ω/sub pe/ then waves exist with phase velocities in the plateau region and these waves are most easily destabilized by the anomalous Doppler resonance, ω - k/sub parallel/v/sub parallel/ = -ω/sub ce/