Full-Wave Analysis of Lower Hybrid Wave Propagation in the Edge Plasma of a Tokamak

Recent lower hybrid current drive\textbf{ (}LHCD) experiments on Alcator C-Mod have revealed a transition density above which LHRF generated fast electrons are no longer detected [1]. This critical density is also well below the threshold density for parametric decay of the LH pump wave. Analysis of these plasmas using a ray tracing-Fokker Planck model shows that poorer wave penetration at higher density, accompanied by increased collisional damping in the Scrape off Layer (SOL) may possibly explain this transition [1]. We have used an electromagnetic field solver TORLH [2] to begin to assess the possible role of full-wave effects in this density limit. Results will be presented, including three-dimensional field reconstructions for varying edge plasma parameters such as SOL density, temperature, and density gradient scale length. \\[4pt] [1] G. Wallace \textit{et al}, 18$^{th}$ Topical Conf. on RF Power in Plasmas (Gent, Belgium, June, 2009) Paper B60. \\[0pt] [2] J. C. Wright \textit{et al}, Physics of Plasmas \textbf{16}, July (2009).