Frequency-step-tunable high-power gyrotron for plasma physics applications

In this work we discuss how to tune the frequency of a high-power gyrotron. The importance of this problem increases in the case of using gyrotrons in large-size fusion machines. The point is that the magnetic field in large stellarators and tokamaks considerably changes over the distance from the plasma center to its boarder. This means that the resonance condition between the plasma electrons and the gyrotron signal is fulfilled only in a relatively small layer of the plasma. To reach other plasma layers one must either use mechanically steerable mirrors to direct the RF wave to the desired position and to employ the Doppler shift effect, or change the frequency of the source and, hence, the position of the resonance layer in the plasma. It is quite obvious that the second possibility is more attractive, because it reduces the number of mechanically movable parts close to the plasma in a fusion machine and increases reliability of operation of the entire system.