Advances in Lower Hybrid Current Drive for TOKAMAK long pulse operation: Technology & Physics

Abstract

The paper gives a picture of the present status and understanding of technology and physics of Lower Hybrid Current Drive for long pulse operation in tokamaks, including the development of continuous wave (CW) high power klystrons, and its evolutions towards ITER. 3.7GH/ 700kW CW klystrons produced in series by Thales Electron Devices are now in operation on Tore Supra. First series of eight klystrons delivered more than 4MW to sustain non-inductive plasmas during 50 s. Moreover, a prototype of 500kW CW klystron operating at 5GHz developed for KSTAR by Toshiba Electron Tubes and Devices, and foreseen for ITER, is able to produce RF output powers of 300kW/ 800 s and 450kW/ 20 s on matched load. The situation on wave coupling and antennas is reported, with the latest Tore Supra results of the new CW Passive-Active Multi-junction (PAM) launcher: the antenna concept foreseen for ITER. First experiments with the PAM antenna in Tore Supra have provided extremely encouraging results in terms of power handling and coupling. Relevant ITER power density of ~25MW/m2 (2.7MW of power injected into the plasma) has been maintained over ~80 s. In addition, LH power of 2.7MW has been coupled at a plasma-antenna distance of 10 cm.