Infrared Measurement of the Temperature Distribution of a Repetitively Pulsed Electron Beam Extraction Foil as a Beam Uniformity Diagnostic

This paper presents results of experiments to measure the current extracted through the foil of an electron beam diode by observing the heating of the foil. Generally anode current density is measured with a dosimeter film, often of dubious linearity, or with Faraday cups which give a current density versus time map at isolated points or with an array of calorimeters. For the present measurements a fast scanning infrared camera is used to measure the temperature rise of the foil after a pulse. The measurement takes 600 μs for a single line scan or 16 ms for a full raster scan. Resolution is comparable to that of dosimeter film, the IR camera is easily calibrated to produce accurate temperature plots, and because of the fast scan this system is ideally suited to observing small scale structure in the beam current density for repetitive pulses up to several hundred Hertz pulse repetition rates.