Development of compact generator complexes based on terahertz clinotrons at O. Ya. Usikov IRE NAS of Ukraine
Authors: A.A. Likhachev, A.A. Danik, Yu.S. Kovshov, S.A. Kishko, S.S. Ponomarenko, E.M. Khutoryan, A.M. Kuleshov, A.S. Tischenko , V.V. Zavertanniy, A.F. Zabrodskiy, S.M. Terekhin, T.V. Kudinova, L.A. Kirichenko, L.A. Galushko, Yu.S. Klescheva, G.S. Bezrodnaya, S.A. Vlasenko
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Subject and purpose. This paper deals with the results recently obtained in Vacuum Electronics Department of O. Ya. Usikov Institute for Radiophysics and Electronics of National Academy of Sciences of Ukraine during the development of compact complexes for generation of electromagnetic radiation in the terahertz frequency range. These complexes with clinotrons as electromagnetic oscillators are intended for carrying out experimental researches in the field of nuclear magnetic resonance spectroscopy using the dynamic nuclear polarization technique.
Methods and methodology. To calculate the frequency characteristics, the model of the beam-wave interaction of clinotron was improved by an algorithm that takes into account mutual transformations and reflections of the surface and highest waves in clinotron electromagnetic system. The methods of statistical analysis of the experimental data of developed and tested clinotrons were applied to clarify the obtained results. The values of the space charge, the optimum oscillation phase shift for the SWS period, the length and Pierce gain parameter depending on the operating frequency were determined.
Results. Transport of the intense electron beams (EB) in slightly inhomogeneous magnetic focusing fields and interaction of EB with RF fields of SWS were investigated theoretically and experimentally. The propagation of surface and highest waves and their mutual transformations on inhomogeneities of clinotron electromagnetic systems were simulated. The RF ohmic losses caused by the surface roughness of the SWS and thermal effects caused by falling EB were studied. The generation of oscillations in packaged clinotrons in the frequency range 120…410 GHz was experimentally obtained. The developed systems demonstrate the frequency stability of the generated electromagnetic radiation at a level of 1 ... 30 ppm in the frequency range of 120...410 GHz and provide level of output power about 100 mW at a frequency of 300 GHz.
Conclusions. The ways of both output power and stability increase in THz clinotrons are proposed. Methods for reduction of the RF ohmic losses effect on the efficiency of beam-wave interaction in THz clinotrons by using multi-stage SWS and electromagnetic systems with a small length parameter have been investigated.