Recent progress on lower hybrid current drive and implications for ITER

TL;DR

This paper reviews recent advancements in Lower Hybrid Current Drive technology, its experimental validation, and implications for ITER, emphasizing the need for further R&D to ensure reliable steady-state plasma operation.

Contribution

It reports on progress in LHCD system development, including experimental validation and modeling efforts, to support ITER's steady-state plasma operation.

Findings

Successful demonstration of LH power coupling at ITER-like densities

Development of high-power RF components for long pulse operation

Ongoing validation of integrated LH modeling suite

Abstract

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