Advances in Lower Hybrid Current Drive for Tokamak Long Pulse Operation: Technology and 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. 3.7 GH / 700 kW CW klystrons produced in series by Thales Electron Devices are now in operation on Tore Supra. First series of eight klystrons delivered more than 4 MW to sustain non-inductive plasmas during 50 s. Moreover, a prototype of 500 kW CW klystron operating at 5 GHz developed for KSTAR by Toshiba Electron Tubes and Devices, and foreseen for ITER, is able to produce RF output powers of 300 kW / 800 s and 450 kW / 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 ∼25 MW/m 2 (2.7 MW of power injected into the plasma) has been maintained over ∼80 s. In addition, LH power of 2.7 MW has been coupled at a plasma-antenna distance of 10 cm.

Science and technology research and development in support to ITER and the Broader Approach at CEA

“…The reflection coefficient is in the range 2-6% [34], even at a plasma-launcher distance of 10 cm or during strong density perturbations in front of the launcher due to supersonic molecular beam injections mimicking ELMs [33]. Recently, successful GJ-grade discharge lasting 150 s (total injected power of 6.3 MW) was obtained with 5.2 MW LHCD and 1-1.5 MW of ICRH [35,36], including real-time feed-back control of RF powers, monitored by IR imaging. Such a discharge is shown in figure 10.…”