Lower hybrid wave excitation by a fast wave current drive antenna

Excitation of the lower hybrid wave (slow wave) using a launcher designed for fast wave excitation has been observed under conditions where neither direct excitation nor mode conversion is expected to take place. The slow wave was revealed through the presence of its resonance cone. The experiment was performed with Ω_i ≪ ω ≪ Ω_e. The coupling of the fast wave into the slow wave is attributed to parasitic excitation, which is a linear mechanism involving electron × motion and charge separation in a density gradient. This process could be a significant loss mechanism for fast wave current drive in toroidal plasmas.