A study is presented of self-space charge effects of tubular electron beams with gyromotion in coaxial cavities. Analytical expressions for the space charge limited current and voltage depression are obtained. The analysis indicates that the coaxial waveguide appears to he more attractive than the hollow cavity, as the coaxial insert greatly alleviates the design constraints associated with the self-space charge depression of the propagating beam. In particular, it is verified that in a 280 Gllz, TE42,7 gyrotron cavity the limiting current for a 90 keV electron beam (with an electron velocity ratio of a = 2.0) raises from 52A to 143A after introducing into the cavity a 5.7-mm-diameter coaxial conductor, which leaves almost unperturbed the operating TE42,7 mode.
R. A. Correa, R. A. Correa,
"Limiting current in gyrotron coaxial cavities", Proc. SPIE 1929, 17th International Conference on Infrared and Millimeter Waves, 192973 (7 December 2017); doi: 10.1117/12.2298372; https://doi.org/10.1117/12.2298372