Experimental measurements of lower-hybrid wave propagation in the Versator II tokamak using microwave scattering

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Abstract
A series of 139 GHz microwave scattering experiments has been performed on the Versator II tokamak (B. Richards, Ph.D. thesis, Massachusetts Institute of Technology, 1981) to study the propagation of externally launched 0.8 GHz lower‐hybrid waves. During lower‐hybrid current drive, the launched waves are found to follow a highly directional resonance cone in the outer portion of the plasma. Wave power is also detected near the center of the plasma, and evidence of wave absorption is seen. Scattering of lower‐hybrid waves in k space by density fluctuations appears to be a weak effect, although measurable frequency broadening by density fluctuations is found, Δω/ω=3×10−4. In the detectable range (2.5<N∥N∥ spectra inferred from the scattering measurements are quite similar above and below the current drive density limit. Numerical modeling of these experiments using ray tracing is also presented.