Electron cyclotron ray tracing and absorption predictions for Compact Toroidal Hybrid plasmas using TRAVIS

Plasmas in the Compact Toroidal Hybrid (CTH), a five field period, $\ell = 2$ torsatron ($B_0 = 0.5$\,T $R_0 = 0.75$\,m, $a_p\approx0.2$\,m) will be heated by second harmonic X-mode electron cyclotron heating with power provided by a 28\,GHz gyrotron capable of producing up to 200\,kW. Ray-tracing calculations that will guide the selection of the launching position, antenna focal length, and beam-steering characteristics are performed with the TRAVIS code [1]. Non-axisymmetric vacuum and current-carrying CTH equilibria for the ray tracing are modeled with the V3FIT code [2]. The calculated absorption is highest for vertically propagating rays that traverse the region where a saddle of resonant field strength exists. However, the absorption for top-launched waves is more sensitive to variations in the magnetic equilibria than for a radial side launch where the magnetic field profile is tokamak-like.\\[4pt] [1] N.B. Marushchenko, Y. Turkin, H. Maassberg, Comp. Phys. Comm. 185 165 (2014)\\[0pt] [2] J. D. Hanson et al., Nucl. Fusion 49, 075031 (2009)