Second harmonic gyrotron based on a 12 T superconducting magnet

Abstract

Near-THz gyrotrons are of interest for applications such as remote sensing, materials processing, and dynamic nuclear polarization (DNP) enhanced nuclear magnetic resonance (NMR) applications. We are setting up a gyrotron test-bed based on a Cryomagnetics 12-T cryogen-free, 3-inch warm-bore, superconducting magnet to investigate second- and higher-harmonic gyrotrons operating at frequencies up to 1 THz. A Varian VUW-8010 triode electron gun originally designed for a 35 GHz gyrotron and driven by a hard-tube modulator will be used initially. The cathode radius is 7 mm and the gun can be operated at voltages up to 70-keV. Adiabatic scaling laws have been used to determine the approximate parameters of the gyrating electron beam that can be produced by this gun in the axial magnetic field profile of the 12-T magnet. The first experiments will operate at the second harmonic at frequencies up to 600 GHz and powers in the kilowatt range. A cavity has been designed with an interaction length of about 1 cm and a Q of 8400. Operating modes of interest include the TE18,2 and the TE57 modes. A Vlasov-type output coupler has been designed using geometric optics. Design calculations and the status of the experiment will be discussed.