Real-time Control of the Deposition Location of ECRH in the LHD

A real-time control system for the deposition location of electron cyclotron resonance heating (ECRH) has been newly developed and applied to experiments on the Large Helical Device (LHD). Appropriate settings for a steerable launcher for ECRH were obtained by evaluating the deposition location and the absorption power for various electron density profiles using a ray-tracing code. The real-time deposition location control system adjusts launcher settings to improve the first-pass absorption of the refracted electron cyclotron wave, based on the ray-tracing calculations. The control system was designed to use a fast field programmable gate array (FPGA). The FPGA processes in real time the calculation of characteristic parameters regarding the density profile and the calculation of target positions requested for rotation control of a steering mirror of the launcher. The real-time deposition location control during ECRH discharges on the LHD functioned successfully in maintaining the absorption power higher than that without the control, which resulted from the deposition location maintained in the plasma core region.