Advances In LHCD System For SST-1 Tokamak

The lower hybrid current drive (LHCD) system, which is a mature, robust, and reliable heating and current drive system in a large number of tokamaks, is designed, developed, and being commissioned on the steady-state superconducting tokamak (SST-1) for driving 220 kA of plasma current, noninductively, for 1000 s, at nominal plasma parameters (plasma density ∼2×10¹⁹ m⁻³, temperature ∼1 keV, toroidal magnetic field ∼3 T), using four 3.7-GHz, 500-kW continuous wave (cw) klystrons. It employs a conventional grill antenna to launch toroidal lower hybrid waves asymmetrically, with a parallel refractive index N_∥ of approximately 2.25 at 90-deg relative phasing of adjacent channels. The system is very complex and requires interfacing with several subsystems such as high-power radio-frequency systems, high-voltage power supply systems, auxiliary power supply systems, efficient thermal management systems, complex networks of transmission line systems, and robust and reliable data acquisition and control systems. With the SST-1 LHCD system as a case study, this lecture gives a broad overview of the physics and design layout of LHCD systems. It addresses cutting-edge technologies employed in realizing the system and gives the present status and advances made for cw operation. The challenges and opportunities are also highlighted.