Experimental evaluation of PPM focussed electron beams

To determine allowable tolerances in TWT manufacturing, a beam tester capable of mapping the beam automatically in three dimensions within the PPM stack has been made operational. Beam position and beam ripple have been measured as a function of beam injection eccentricity, gun tilt, and anode-to-barrel spacing. The influence of cross fields in the PPM stack appears to be severe. Correlation between experimental results and the two-dimensional Hermannsfeldt computer code predictions have been made.