Affiliations: [a] Bharat Sanchar Nigam Ltd, Nodal Cell WiMAX, TPT Nagar,
Ludhiana, Punjab, India | [b] Center of Research in Microwave Tubes, Electronics
Engineering, Institute of Technology, Banaras Hindu University, Varanasi,
India
Abstract: The present paper is devoted to the study of mode competition and
control in a 170 GHz gyrotron cavity for potential application in electron
cyclotron resonance heating (ECRH) of plasmas. An extensive analysis has been
carried out for coupling coefficient, start oscillation current, voltage
depression, and limiting current for the candidate modes in the gyrotron cavity
resonator. The study reveals that the main competing modes for
TE_{28,8}^{-} come from TE_{25,9}^{+} and
TE_{27,8}^{-}. The optimum beam position for
TE_{28,8}^{ - } mode is found to be at 8.28 mm. To avoid
excitation of competing modes, it has been found that slight increase in
electron beam radius from 8.28 mm to 8.40 mm avoids the excitation of all the
competing modes. Based on the considerations of coupling coefficient, start
oscillation current, voltage depression, and limiting current; the
TE_{28,8}^{-} mode is selected as the operating mode.
