Velocity spread in gyrobeams due to cathode edge emission

Summary form only given as follows. In analyzing the design of the magnetron injection gun and beam optical system to be used in the 94 GHz NRL/CPI/Litton gyroklyston, a major source of velocity spread in gyrobreams was discovered. Basically, when we set up a detailed model of the region between the emitter strip and the focus electrodes in DEMEOS (used for the simulations), we observed a large amount of current pouring from the edges of the cathode strip due to the level of field penetrating the gaps. This edge emission caused a major increase in velocity spread (both parallel and perpendicular) over the idealized case and by including it, computed and typical observed results are now in line. In the paper, we will show quantitatively how velocity spread is affected by the gap geometry (cathode and focus electrode edges perpendicular to the axis, perpendicular to the cathode, or parallel to the axis). Also, we will show how edge emission affects /spl alpha/, and explain why a cannot be increased beyond a certain level (lower than theory predicts) without mirroring. We will show the difference in results due to use of a thermal beam model, and the inclusion of self-magnetic field. Finally, we will present means of reducing or eliminating edge emission in order to bring velocity spreads down.