Dynamicsofa Very Intense Pulsed electron Beam

Abstract

A unique beam of pulsed electrons has been developed using the 19-MeV, 700-kA Hermes-III accelerator. The extended planar-anode diode is used to extract at large radius an annular electron beam from the accelerator and inject the resulting beam at small angle into a low-pressure gas cell, where the beam is rapidly charge neutralized and almost current neutralized. Under these conditions, the beam propagates nearly ballistically to a focus downstream of injection, where objects can be placed for irradiation and study. For a focal length of 78 cm, measurements with a segmented calorimeter show that this configuration can deliver an energy deposition of 200 J/g [20 Mrad] over a useful area of 70 cm{sup 2} and a 4-cm depth in graphite in 25 ns. Increasing the injection angle by reducing the AK gap permits higher doses over smaller areas to be achieved. Such beams are of interest for the study of material property changes from short-pulse high-energy depositions and for the study of electronic components response to thermal mechanical shock. The MAGIC/CYLTRAN model prediction of the radial energy deposition profile in the calorimeter is in excellent agreement with that measured at the focus. This experimentally verified model predicts that a peakmore » dose of 3,800 J/g (too high to be easily measured) with a HWHM radius of 1.3 cm can be generated at the focus in graphite if the focal length is decreased to 11 cm.« less