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Megawatt Power-Level G-band Planar Gyrotrons with Transverse Energy Extraction

Modern controlled-fusion facilities are equipped with electron-cyclotron plasma fusion systems based on gyrotron complexes, in which the maximum continuous-wave radiation power has been achieved at a megawatt power level in the millimeter wavelength range. At the same time, a higher frequency of microwave sources is required for novel compact fusion reactors with strong magnetic fields. For example, the DEMO reactor project, which is intensely discussed at present, requires development of shorter-wave megawatt continuous-wave sources having a frequency of 220–260 GHz. As such sources, we suggest gyrotrons of planar geometry of interaction space with a sheet electron beam and transverse energy extraction. An advantage of this scheme in comparison with conventional cylindrical geometry is the possibility to ensure effective mode selection over the open transverse coordinate in combination with radiation outcoupling that leads to a substantial reduction of Ohmic losses. In this paper we perform theoretical analysis and numerical simulation of two G-band planar gyrotrons operating at the first harmonic of the cyclotron frequency. First, 140 GHz planar gyrotron driven by a sheet helical electron beam with an energy of 50 keV and beam current of 30 A is studied. The project of this oscillator is under development at Institute of Applied Physics RAS currently. Finally, simulations of 260 GHz megawatt power planar gyrotron for DEMO project are considered.