Conceptual Study of Multi-Megawatt Millimetre-Wave Transmission and Antenna Systems for Electron Cyclotron Wave Applications in NET / ITER

A parametric study of multi-megawatt mm-wave transmission and launching antenna systems for various electron cyclotron wave (ECW) applications in next generation thermonuclear fusion devices such as NET or ITER has been carried out for the frequency range between 120 and 260 GHz. The paper presents a conceptual design of a 140 GHz, 20 MW, CW reference ECW system to assist gas breakdown, plasma formation and pre-heating, and for local current density profile control by “upshifted” noninductive current drive (ECCD) near the q = 2 magnetic surface in order to prevent major disruptions. The ECW system will preferably be made up from 1 MW, CW mm-wave generator and transmission units (comprised of gyrotron, transmission line and torus barrier window) and one common quasi-optical antenna module. The evacuated transmission lines combine the advantages of HE 11 - mode waveguide and TEM OO - mode quasi - optical components. Tracking of the q = 2 surface is achieved by sweeping of the mm-wave beam in a horizontal plane (15°–25°) using one rotatable reflector in the 4-mirror antenna system. The expected total mm-wave transmission efficiency from the gyrotrons to the plasma is approximately 85%.