Non-canonical gyrotrons

Abstract

Scientific research in the 60s of the last century led to the creation of gyrotron and a number of other gyrodevices, the principle of the its actions are based on the synchronous interaction of the curved electron beam and an electromagnetic wave: the combined effect of relativistic effects and non-homogeneity of high-frequency field on the trajectories of electrons in a magnetic field leads to the intensive cyclotron radiation at the gyrofrequency and its harmonics [1]. The canonical gyrotron version includes adiabatic magnetron-injection electron gun (MIG), forming a tubular helical electron beam (HEB), oversize, weakly irregular cylindrical cavity with a diffraction radiation output, the output window of rf radiation and electron beam collector. Design of powerful gyrotron as a rule, further includes a built-in quasi-optical mode converter and depressed collector for recovery of the residual energy of the electron beam. The axial symmetry of canonical gyrotron and absence of its small-scale elements are favorable for its industrial development. For small and medium-power gyrotron for technological applications and spectroscopy efficiency increasing and frequency tuning are desirable.Over the past few years in a number of leading countries created a high level of high-performance powerful gyrotrons from centimeter to submillimeter range [1][2][3]. Several fundamental scientific fields are formed, the successful development of which is directly caused by the presence of these sources (plasma heating in controlled thermonuclear fusion, development of technology of new materials, spectroscopy (EPR and dynamic nuclear polarization of NMR) and others. Each of the applications dictates own direction of development of gyro-devices, which are analyzed in this paper. For the gyrotron of low power for spectroscopy the customers have high demands for long-term stability and frequency tuning, increase of efficiency. However the complexity of the task is exacerbated by the problem of mode competition and high ohmic losses, especially in gyrotrons operating in the sub millimeter wave range on harmonics of the cyclotron frequency [2][3][4][5].Due to a various reasons during the process of achieving of the maximal energetical characteristics (output power, efficiency, pulse energy), a number of gyro devices, other than the canonical gyrotron version, fizzled out and now were on the sidelines of progress. Such noncanonical devices have partitioned active medium, or (and) the space of interaction; non-cylindrical (ribbon or thin axial) helical electron beam (HEB); oversized strongly non-cylindrical or coaxial, quasi-optical, echelette cavities, etc. However, in the canonical gyrotron are insufficient selective properties at work on the gyro frequency harmonics and very limited possibilities for frequency tuning. The report analyzes the perspectives of non-canonical gyrotron in terms of frequency tuning and improved mode selection working on the gyro frequency harmonics.Separation of an electron flow for several partial beams g...