Space charge effects of gyrotron electron beams in coaxial cavities

Analytical expressions for the space charge limited current and voltage depression of tubular electron beams propagating in the cylindrical coaxial waveguide are derived. Results for electron beams of diverse characteristics are discussed. Regarding space charge effects, the coaxial waveguide appears to be more attractive than the hollow cavity. In particular, it is verified that in a 280GHz TE42,7gyrotron cavity the limiting current for a 90 kV, α = 2.0 electron beam raises from 52 A to 143 A after introducing into the resonator a 5.7 mm diameter coaxial conductor, which leaves almost unperturbed the operating TE42,7 whispering gallery mode.