Lower hybrid wave coupling and propagation in the presence of nonthermal edge electrons

In order to improve our understanding of lower hybrid current drive experim ents in high power regimes, where fast electrons (up to few keV) are genera ted in front of the lower hybrid (LH) grill, an analysis of LH wave couplin g and propagation is carried out using a formulation of the dielectric tens or that incorporates the fast electron population (T-hot less than or simil ar to 5 keV). It is found that both the real and imaginary parts of the die lectric tensor are modified for waves with \N-parallel to\ greater than or similar to 10, which can interact with the fast electrons through Landau da mping. Consequently high N-parallel to waves can be absorbed within less th an 1 cm, or even cut-off at the grill-plasma interface. Antenna-plasma coup ling code results show that the power available to accelerate electrons in front of the grill (launched power with \N-parallel to\ > 10) decreases in the presence of fast electrons. Also, despite strong modifications of the d ielectric tensor, and of the power transfer to high N-parallel to waves, th e presence of fast electrons (T-hot less than or similar to 5 keV) leads to only moderate changes of antenna reflectivity and directivity. (C) 1999 Am erican Institute of Physics. [S1070-664X(99)03301-7].