A generic mode selection strategy for high-order mode gyrotrons operating at multiple frequencies

Abstract

High-power, high-frequency gyrotrons for electron cyclotron resonance heating and current drive, such as proposed for the demonstration thermonuclear fusion reactor DEMO, require operating modes of very high order. As it is shown, the selection of the operating modes for such gyrotrons can be based on multi-frequency operability. A general selection strategy is derived, suitable for multi-purpose multi-frequency gyrotrons with quasi-optical mode converter and single-disc output window. Two examples, one of them relevant for future DEMO gyrotron designs, are discussed.

Design and analysis on a 0.1‐THz second harmonic low‐voltage, low‐current gyrotron with complex cavity

“…In order to make a quasi‐optical mode converter with high efficiency available for the gyrotron in the future, the output mode should be convertible to Gaussian mode. In principle, the quasi‐optical launcher design relies heavily on the relative caustic radius of the designed mode, since this radius defines the Brillouin zone . The relative caustic radius C K can be defined as C K = m / μ mn , where m and μ mn are the azimuthal index and the eigenvalue of TE mn , respectively.…”

Interaction circuit design and RF behavior of a 236 GHz gyrotron for DEMO

“…Along with these specifications, it is also preferred to use a quasi-optical mode converter for the axial output and a single disk CVD-diamond RF window [9]. The basic principles of mode selection for a highfrequency high-power gyrotron operating at very high-order modes have been explained in [10,11]. In there, it has been shown, that primary criterion for mode selection can be the possible multi-frequency operation of the gyrotron, rather than the selection of specific spectral properties for the operating modes and its main competitors.…”

Mode selection and interaction structure design of a megawatt class, sub-THz wave coaxial cavity gyrotron

“…DEMO tokamak requires gyrotron delivering continuous wave RF power at the frequency of above 200 GHz for the proper current drive and output power of above 1 MW with the efficiency of above 60% for the proper fusion gain factor. Further, multi-frequency gyrotron have added advantage for the use in plasma devices with different central magnetic fields [3].…”

“…In this paper, mode selection and interaction structure design of a 2 MW, 204 GHz coaxial cavity gyrotron is presented. Based on the mode selection strategy given in [3] operating mode has been chosen. Cold cavity analysis for the coaxial cavity gyrotron with rectangular corrugated insert has been done and the interaction structure has been designed.…”