Analysis of the excitation conditions of the higher oscillation modes in an orotron

One-dimensional theory with allowance for space charge is used to analyze starting currents for the higher oscillation modes in a spherical-mirror orotron. Starting currents are determined for TEMmnq modes, in cases of m = 0, n = 1; m = 0, n = 2; and m = 1, n = 0. It is shown that as the space charge increases the ratio of the starting currents for the higher modes to the starting current for the fundamental mode decreases.