NIFS-585

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Author(s):

R. Kumazawa, T. Mutoh, T. Seki, F. Shinpo, G. Nomura, T. Ido, T. Watari, Jean-Marie Noterdaeme and Yangping Zhao

Title:

Liquid Stub Tuner for Ion Cyclotron Heating

Date of publication:

Feb. 1999

Key words:

liquid stub tuner, ICRF heating, feedback control, high power/steady state heating

Abstract:

Ion Cyclotron Range of Frequency (ICRF) heating on the Large Helical Device (LHD) is characterized by high power (up to 12MW) and steady state operation (30 minutes). The LHD is a helical device (with a major radius of 3.9m and a minor radius of 0.6m) with super-conducting coil windings (1=2, m=10). The main purpose of physical research is to investigate currentless and disruptlon-free plasma. Research and development for steady state ICRF heating has been carried out in recent years: A high RF power transmission system consisting of stub tuners, a ceramic fee-through and an ICH loop antenna has been developed In addition, steady state operation of an RF oscillator has been achieved at a power higher than IMW. A liquid stub tuner has been proposed as an innovation. The liquid stub tuner makes use of the difference between the RF wave lengths in liquid and in gas due to the different relative dielectric constants. The liquid stub tuner has been experimentally proved to be a reliable RF component for high power transmission systems. Test results have quantitatively demonstrated that it can be used at high RF voltage: 6lkV for 10 seconds and 50kV for 30 minutes. Furthermore, the liquid surface can be shifted under high RF voltage without breakdown, which suggests that it can be employed as a feedback control impedance matching tool to keep reflected RF power at a low level with regard to a temporal variation of plasma loadlng resistance.

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