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Gyrotrons are millimetre wave oscillators based on the electron cyclotron maser (ECM) instability, whose main application is for heating in fusion devices, supplying close to 1 MW of CW at a frequency around 120-200 GHz. To maintain the ohmic loading at a reasonable value (less than a few kW/cm2) the resonant structure is largely overmoded and is either a TE(m,n,1) (m greater than 20, n greater than 1) cylindrical cavity or a TEM(0,0,q) (q = 200-400) Fabry-Pérot resonator. This requirement leads to competition between the modes within the bandwidth of the ECM instability. This paper discusses theoretical advances in the simulation of the time evolution of the electromagnetic fields of the different resonant modes, with particular reference to the influence of the start-up. The design of the gun electrodes and the degradation of beam quality by instabilities in the beam tunnel are considered. Finally technical approaches to increase the electrical efficiency are outlined.

Additional information

Authors: TRAN M Q, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne (CH)
Bibliographic Reference: Article: Proceedings of the 17th International Conference on Infrared and Millimeter Waves, Vol. 1929 (1992)
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