Analyzer for profile measurement of a beam from a magnicon electron gun

Summary from only given, as follows. A key parameter in determining the efficiency of a magnicon amplifier is the quality of the electron beam used to drive the device, and in particular the diameter of the electron beam and its matching into the axial magnetic field. The electron gun for the 11.4 GHz magnicon amplifier experiment at NRL is an ultrahigh-convergence Pierce-type gun designed to produce a 480-kV, 210-A electron beam of diameter less than 2 mm. A novel beam analyzer has been built to characterize this beam, with a design based on a similar analyzer used for measuring the beam of an earlier magnicon. The analyzer allows the beam profile to be monitored as changes are made in the magnetic flux linking the cathode, and with changes in the bias on the cathode focus electrode. The analyzer makes use of ten graphite apertures that are mounted at 30/spl deg/ intervals on an off-axis rotating drum, so that only a single aperture will intercept beam current at one time. The drum is rotated by a stepper motor, and its precise rotation is read out to an accuracy of better than 0.1/spl deg/ using a digital shaft encoder, permitting spatial measurements with an accuracy of better than 60 microns. The apertures are spaced at 1-cm intervals along the beam axis, a spacing that permits resolution of beam scalloping and centroid displacement effects. These apertures are designed to measure only the position of the beam edges, since interception of the maximum current density of up to 12 kA/cm/sup 2/ would destroy the graphite apertures. The analyzer also includes two ten-cm graphite tubes, of 4 and 8 mm inner diameter, at the remaining two angular stations, for use in measuring the net transmitted and intercepted current. This paper will describe the calibration of the beam analyzer, and its application to the measurement of the magnicon electron beam.