The trajectories for an image intensifier with an Einsel lens used to focus the electrons normal to the target.
The image intensifier shown above uses a lens to bring the electrons from the emitter normal (+ or - 1.5 degrees) to the target so that the target would respond uniformly with respect to the incoming electrons. The beam is extracted when the grid in front of the target is turned on. Focusing at the target is controlled by the large intermediate electrode. There is a screen at both the entrance and the exit from the lens to minimize distortion. The radial starting point of each of the particles can be plotted against the radial position at the target so that a measure of the distortion can be obtained.
Plot of the particles' position along the cathode (RLOC) vs. the radius (R) at the target.
Trajectories normal to the cathode and at +/- 45 degrees can be computed to determine the focusing of the image at the target. The emittance plot and the current distribution at the target are shown below. The emittance plot shows an angular distribution of +- 25 milli radians (1.5 degrees) at the target. The current density distribution is nearly uniform at the target.