Ion contamination of x-ray pinhole camera images on PBFA II

Abstract

Inner-shell x-ray pinhole cameras are an important diagnostic for time-averaged beam profile measurements on PBFA-II experiments which requires no shielding from the diode magnetic field. However, the same ions that create the inner-shell x rays can also Rutherford scatter and directly expose the x-ray film. A double image, due to this effect, has been observed in PBFA-II data. In this paper, we derive the expected film density due to these scattered ions relative to the film density from the ion-induced x-ray line radiation from titanium, aluminum, and gold targets. We then show that our calculated degree of ion contamination for a gold target Mα camera recently fielded on PBFA-II is consistent with the actual images observed−a phantom image tentatively identified as proton contamination with a film density of the same order of magnitude as the x-ray image. The amount of ion contamination is strongly dependent on the optical filtering used. For less heavily filtered cameras, we will show that this contamination will be less of a concern. We propose a different camera geometry for which this ion contamination will be a 5% effect in the titanium and aluminum Kα cameras, but may be a 16% effect in the gold Mα cameras.