Recent progress on lower hybrid current drive and implications for ITER

Abstract

The sustainment of steady-state plasmas in tokamaks requires efficient\ncurrent drive systems. Lower Hybrid Current Drive (LHCD) is currently the most\nefficient method to generate a continuous additional off-axis toroidal plasma\ncurrent as well as reduce the poloidal flux consumption during the plasma\ncurrent ramp-up phase. The operation of the Tore Supra ITER-like LH launcher\nhas demonstrated the capability to couple LH power at ITER-like power densities\nwith very low reflected power during long pulses. In addition, the installation\nof eight 700kW/CW klystrons at the LH transmitter has allowed increasing the\ntotal LH power in long pulse scenarios. However, in order to achieve pure\nstationary LH sustained plasmas, some R\\&D are needed to increase the\nreliability of all the systems and codes, from the RF sources to the plasma\nscenario prediction. The CEA/IRFM is addressing some of these issues by leading\na R\\&D program towards an ITER LH system and by the validation of an integrated\nLH modeling suite of codes. In 2011, the RF design of a mode converter has been\nvalidated at low power. A 500 kW/5 s RF window is currently under manufacturing\nand will be tested at high power in 2012 in collaboration with NFRI. All of\nthis work aims to reduce the operational risks associated with the ITER\nsteady-state operations.\n