Recent advances in gated x-ray imaging at LLNL

Abstract

The Inertial Confinement Fusion program at LLNL is becoming increasingly dependent on time-resolved, two-dimensional X-ray imaging for measurement of target dynamics'. A gated X-ray imaging module has been developed over the last several years and has evolved into a design. This design makes use of primarily mass-produced components, with customized image area characteristics defined by the geometry of an electrode evaporated onto the front surface of a microchannel plate (MCP). As a result, we now have eight imaging modules operating on Nova and will be adding five more in the next few months. In the past year, in addition to assembling and installing gated imaging modules, we have also measured their performance characteristics and investigated possible enhancements for future (or retro-fitted) modules. We have been looking at the entire process from detection of an X-ray photon to digitization of the photographic film. A companion paper2 describes efforts to further reduce the aperture time by using thinned MCP's. In this paper, we focus on results associated with the spatial resolution and noise of the imaging module and the image recording process. We first present the performance characteristics of the standard imaging module; then describe potential enhancements to the performance. In the course of this work, we made measurements of the transverse electron energy distribution at the exit of the MCP. Results are reported for both DC and pulsed MCP bias voltage, and the differences are analyzed. We also investigated an alternative phosphor screen and studied the noise and sensitivity of various photographic films.