A particle simulation study of self-bias potential for plasma ion confinement in multiple-pulse radiography

Abstract

Summary form only given, as follows. The intense deposition of energy on to a high-Z target from a high current relativistic electron beam produces bremsstrahlung photons which can be used to generate radiographs of a dynamically evolving object. The interaction of the intense electron beam with the target can generate plasmas from the target surface. Consequently, a column of plasma ions expands away from the target due to the space charge potential of the electron beam. This expansion can lead to a larger beam spot size resulting in degradation of spatial resolution of radiographic images. Previous studies have shown that a self-biased electric potential between the target and the collimator can confine the ion column and maintain the electron beam spot size. In this work a two-dimensional particle-in-cell code is used to study a novel target configuration in which the converter target and the beam dump are connect electrically to maintain the self-biased potential in multiple-pulse radiography such as in the second axis of DARHT. Our simulation study showed that the self-bias electric potential between the target and the collimator was effective in confining the ions emitted from the target during multiple-pulse operation. The effects of the inductance of the target chamber on the decay time of the self-biased potential are also examined.