Liquid impedance matching system for Ion Cyclotron heating

Ion Cyclotron Range of Frequency (ICRF) heating on the Large Helical Device (LHD) is characterized by high power (up to 12MW) and by steady-state operation (30 minutes). Research and development for ICRF heating have been carried out in recent years. A newly developed liquid stub tuner has demonstrated highly reliable performance as a stub tuner; it has withstood 63kV for 10 seconds and 50kV for 30 minutes. The liquid surface level could be shifted under high RF voltage without breakdown. A liquid impedance matching system has been designed and fabricated for ICRF heating on the LHD. This system consists of a liquid stub tuner and a liquid phase shifter. The liquid phase shifter was constructed by connecting two liquid stub tuners in a U-shaped configuration. An impedance matching can be acquired in a wide frequency range, i.e., 25-95MHz by selecting the length of 4m for the liquid stub tuner. At some frequencies, it was a problem that the RF voltage at the phase shifter became higher than that between the RF antenna and the impedance matching system. However, this difficulty has been resolved by adopting the use of asymmetrical heights of liquid surface levels at the U-shaped liquid phase shifter