Thermal and mechanical effects on gyrotron gun anode electrical performance

A magnetron injection gun operating with temperature limited electron emission has been designed for a gyrotron amplifier. A series of computer models of the gun anode region were used to determine selected thermal and structural characteristics. Their effects on electron beam energy, velocity spread, and temperature were evaluated. The thermal analysis yielded the steady state temperatures of 137 node points, Thermally induced mechanical expansions were found to be 0.20% axially and 0.8296 radially. In the three dimensional coordinate system utilized, the stresses in 373 elements were numerically evaluated, The cathode heater warm-up characteristic was such that a 9 watt input heater power brought the cathode emitter up to 1068°C in 500 seconds. The cathode cooling due to electron emission was found to increase the steady state heater input power requirement by 1196 (for an emitter temperature of 1065°C) from 9 W to 11 W. The electron trajectory analysis included an evaluation of the beam energy, velocity spread, and temperature. The effect of the deformed mechanical shapes on the beam parameters was determined. A two dimensional computer simulation was used to graphically depict the electron trajectories in the gun anode region.