Alignment of an x-ray imager line of sight in the National Ignition Facility (NIF) target chamber using a Diagnostic Instrument Manipulator (DIM) and Opposed Port Alignment System (OPAS)

Abstract

The National Ignition Facility (NIF) fields multiple varieties of x-ray imaging systems used to diagnose the implosion physics of laser-driven fusion targets. The imagers consist of time-resolved x-ray detectors coupled with a snout assembly for spatial and/or spectral imaging. The instrument is mounted onto a cart that extends into the NIF target chamber, placing it in close proximity to the target and aligning with a tight tolerance using the Opposed Port Alignment System (OPAS). The OPAS is a modified, commercial Schmidt-Cassegrain optical telescope mounted at the target chamber port, opposite the Diagnostic Instrument Manipulator (DIM). In this paper, the approach used to characterize and align the x-ray imaging instruments is described. The characterization includes offline measurements of the pinhole assembly and the detector housing. Online, deviations of the DIM, as it is inserted along rails toward the target chamber center, are characterized and related to the OPAS view. An overview of the offline measurement stations is provided along with the process to develop the relationship between the offline alignment scopes and the OPAS as a function of DIM insertion. The combination of these measurements is used to mathematically construct the predicted location of the x-ray imager line of sight in the OPAS image space and determine the desired pinhole location to record data on a fusion experiment. The alignment accuracy of this approach will be discussed, as demonstrated with various x-ray instruments and pinhole configurations.