Measured performance of magnetron injection guns for gyrotrons
Magnetron injection guns (MIGs) are a principle component in gyrotrons and gyroklystrons. The performance of the RF device critically depends on the performance of the MIG that provides the electron beam. Unfortunately, recent measurements indicate that MIGS often generate asymmetrical electron beams that can adversely impact the operation of the RF source. This presentation will describe the measurement facility and provide results from recent tests.
Experimental study of gyrotron efficiency enhancement by improvement of electron beam quality
The methods for suppressing parasitic low- frequency oscillations (LFOs) have been applied to improve electron beam quality in a 4-mm 100-kW gyrotron. In the conditions of suppressed LFOs and of high cathode emission uniformity, the stable operation of this gyrotron at pitch factor values high than 1.5 has been achieved. As a result, the efficiency of the gyrotron at the main TE12,3 mode has been increased from 32 % (corresponds to the designed regime with pitch factor of 1.28) up to 42 %.
Effect of the azimuthal inhomogeneity of electron emission on gyrotron operation
Gyrotrons are typically driven by electron beams produced by magnetron-type thermionic electron guns operating in the regime of temperature limited emission. Very often, the current density in such annular electron beams is azimuthally nonuniform. To describe the effect of this nonuniformity on gyrotron operation, the code MAGY [M. Botton et al., IEEE Trans. Plasma Sci. 26, 882 (1998)], which is widely used for modeling of slow and fast microwave sources, was properly modified. The results of numerical simulations demonstrate the effect of azimuthal inhomogeneity of the emission on the excitation of low- and high-frequency satellites of the operating mode and on the efficiency degradation. The calculations are done for parameters typical for megawatt-class, long-pulse, millimeter-wave gyrotrons, which are currently under development for electron cyclotron plasma heating and current drive experiments in controlled fusion reactors.