Abstract
In the last Large Helical Device (LHD) experimental campaign, a 154GHz gyrotron which had been conditioned to generate 1 MW/2 s, 0.5 MW/CW was installed for LHD experiments. Four high power gyrotrons (three-77 GHz/1~1.5 MW and one-154 GHz/1 MW) and a CW gyrotron (84 GHz/0.2 MW) are ready. Our experiment requires high energy and various injection patterns for Electron Cyclotron Resonance Heating (ECRH). Higher individual injection power and various injection patterns, we developed a power enhancement method by stepped anode acceleration voltage control and operated the gyrotron in the hard excitation region. These operations were realized by a remote controlled waveform generator. However the oscillation map of high power or long pulse operation in the hard excitation region were limited because in order to achieve the hard excitation region by the anode voltage control one must pass through the high anode current phase within a time short enough that the anode or the anode power supply is not overloaded. This limitation becomes more critical when the gyrotron beam current is increased in order to increase the output power. In the long pulse operation it was impossible to reach the hard excitation region in a low beam current (<10A).
Highlights
A gyrotron is a kind of a vacuum tube, which is used as an amplifier, a controller of high voltage, an accelerator, or heating devices of plasma
The transmission lines are acceptable to transmit high power microwave that diffracts heat load, because the load is removed by cooling jacket with which covered around waveguide
It is difficult to determine the waveform of Va by suddenly increasing the anode current (Ia), and the oscillation range is very small in the hard-excitation region
Summary
A gyrotron is a kind of a vacuum tube, which is used as an amplifier, a controller of high voltage, an accelerator, or heating devices of plasma. Gyrotrons have been developed as a power source with several frequencies that are suitable for heating a magnetic confined plasma. The ECRH system consists of gyrotrons, power supplies, transmission lines, launchers, and controllers. Gyrotrons generate heating power and the power is transmit through the transmission line including waveguide, miterbends, and polarizer in evacuated condition. The transmission lines are acceptable to transmit high power microwave that diffracts heat load, because the load is removed by cooling jacket with which covered around waveguide. All the lines are evacuated in order to avoid the arcing by the high power microwave, and the load is used in the vacuum condition. We have developed a suitable water load for our ECRH system
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