Ray Tracing Calculation of ECRH Power Absorption Profile in Heliotron J

Power absorption profiles of electron cyclotron resonance heating (ECRH) are calculated for a helical-axis heliotron device, Heliotron J, by a ray tracing code, TRECE. The three-dimensional structure of flux surfaces and magnetic field is considered to evaluate the power absorption profile accurately. The calculation results show that the power absorption profile can be generally controlled under the experimental conditions of the 70 GHz ECRH system by setting the appropriate launching condition. The well localized single pass power absorption can be realized when the ECRH power is launched with a tokamak-like B contour. The single pass absorption efficiency is as high as 92 % of the injected power in the case of moderate toroidally oblique launch because of the long path along the resonance region. On the other hand, the power is fully absorbed when ECRH power is perpendicularly launched at the poloidal cross section with a saddle-type B contour, although the absorption profile is wider. This is because the magnetic field gradient is gentle at the resonance region. These indicate that the control of power absorption is possible with the appropriate launching condition in the spatially winding plasmas. The calculation is compared with the experimental results on the ECRH plasma on Heliotron J.