Development of steady-state ICRF heating for LHD

An ion cyclotron resonant frequency heating system for steady-state operation of the large helical device (LHD) was developed and tested. A research and development test set-up which consists of a transmitter, transmission lines, matching stubs, a vacuum feedthrough, a vacuum chamber and a test antenna has been constructed. To remove the resistive heat load generated by the r.f. current, all the components are cooled with water which circulates inside them. The structure of the water inlet-outlet of the coaxial transmission lines was newly designed and tested. The coaxial line has a large diameter, 240 mm, in order to ensure a high r.f. stand-off voltage. The steady-state operation test was carried out at 30 kW (which is equivalent to 500 kW in the heating experiment) for 30 min. Temperature increments of the test antenna and the outer conductors of the transmission line are measured and it was confirmed that they stay within the acceptable level. The 30 min test run shows that the newly designed integral components have a high cooling capability and stand-off voltage for the steady-state heating experiment in the LHD.