Computational studies of X-ray framing cameras for the national ignition facility

The NIF is the world´s most powerful laser facility and is used for inertial confinement fusion experiments. One hundred and ninety two laser beams are used to compress a small capsule. X-ray framing cameras are an important diagnostic used to help characterize the dynamics of the capsule. The gated x-ray framing cameras consists of several key components including a pin hole array, microstrips, microchannel plate (MCP), pulsed phosphor, and either film pack or CCD for recording images [1]. The pin hole array is a thin piece of tantalum with small holes used to shield most of the incident x-rays, but allows some to be projected onto a microstrip/MCP. When photons strike the microstrip/MCP photoelectrons are created which can be accelerated through pores in the MCP by pulses on the microstrips. The electrons are amplified in the pores by a secondary electron cascade. At the output of the MCP the electrons are accelerated to a phosphor screen where the output is recorded. The x-ray framing cameras have provided excellent information. As the yields at NIF have increased and the data provided by the framing cameras have been further resolved, some “streak” artifacts were discovered that needed further understanding [2]. A theory was proposed as to the origin of these artifacts [2], as well as a mitigation strategy [2]. In this paper we will discuss the results of electrostatic, full wave electromagnetic, and particle-in-cell simulations used to further understand the streaks in the data as well as simulation results for the mitigation strategy used to help correct the problem. We will also discuss some simulation results that illustrate potential enhancements for future framing cameras.