An Analysis of the Correlation between the Beam Discharge Lag and the Scanning Electron Beam Performance in Pickup Tubes

Abstract

In order to find out clues for improving the beam discharge lag in widely used photoconductive pickup tubes with blocking contacts, the author looked into the following aspects in the scanning electron beam performance as the factors affecting the lag : (1) Energy distribution broadening due to relaxation in the scanning beam. (2) Beam convergence angle on the target. (3) Angle of incidence of the beam on the target. (4) Local distribution of contact potential difference between target and cathode. (5) Second exponential region of the beam acceptance curves.
The author has worked out a computational procedure to follow the surface potential variation on the target and investigated the correlations among the beam performance, the resultant beam acceptance curves and the beam discharge lag.
It is concluded that the relaxation has the most predominant effect and that the other factors add only minor influence on the decay lag characteristics due to beam discharge.