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With advantages of small size, light weight, and fast tuning capability, electronic impedance synthesizer (EIS) presents game-changing opportunities for industry. However, their widely acceptance is still restrained by the understanding of powerhandling capacity and linearity issues. This work addresses both issues through the development of a voltage distribution theory which enables simulating voltage at the position of every PIN diode in the distributed EIS. It provides a way of understanding and predicting the power-handling capacity and nonlinearity of EIS from its linear region. As an example of validation for this theory, a 12-bit EIS along with an automatic measurement setup is presented. Experimental results show a good match among measurement, simulation, and analytical model. The 1 dB compression point (P1dB) of the EIS is larger than 35 dBm, and the third-order input intercept point is larger than 57 dBm. Since the proposed theory is validated, it is possible to be used as a criterion in the optimization process to enhance the power-handling capacity and linearity. Potential applications of such high-linearity EIS can be found in Load-Pull systems, noise measurements, variable impedance loads, tunable matching networks, reconfigurable components, and so on.

Ion cyclotron range of frequency (ICRF) heating on the large helical device (LHD) is characterized by high power (up to 12 MW) and steady state operation (30 min). The LHD is a helical device (with a major radius of 3.9 m and a minor radius of 0.6 m) with superconducting coil windings (l=2, m=10). The main purpose of physical research is to investigate currentless and disruption-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 feedthrough, and an ion cyclotron heating loop antenna has been developed. In addition, steady state operation of a rf oscillator has been achieved at a power higher than 1 MW. A liquid stub tuner has been proposed as an innovation. The liquid stub tuner makes use of the difference between the rf wavelengths 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: 61 kV for 10 s and 50 kV for 30 min. 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 loading resistance.

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