The XDS comprises three primary components: a high-resolution, dual-axes imaging system for repeatable, accurate target positioning; a helium enclosure with triple-axes micrometer positioning; and an Amptek silicon drift detector (SDD). The SDD was fit with a silicon nitrate (Si3N4) window to measure x-ray energies from 200 eV to 40 keV. The detector features a 25-mm2 silicon drift diode with a measured 130-eV full-width-at-half-maximum resolution at 5.7 keV.
Two factors can lead to underfilling a target: (1) The permeation time constant of the shell wall is underestimated so sufficient time is not allowed for the gas pressure inside the target to equilibrate with the charging pressure, or (2) a defect develops in the shell, causing the target to depressurize more rapidly than predicted by the permeation time constant. The target-filling process starts with an evaluation of the D2 permeation rate of the target at General Atomics after fabrication. Upon arriving at LLE, the targets are charged with a desired fill pressure of DT. The β particle decay of tritium atoms within the DT fuel generates both fluorescent and bremsstrahlung x rays as the β particles interact with the shell material. The T2 permeation half-life can be determined for each target by measuring the x-ray activity over a period of a few minutes. In test cases, the premeation time constant of filled targets were measured over several days to compare with the D2 and DT time constants. After considering the root-mass difference for DT and T2, the measured half-lives were observed to be between 2 and 7 times longer than the corresponding D2 half-lives, depending on the age of the DT-filled target. The activity of the tritium bound to the shell was observed to be proportionate to the initial fill pressure. The shell activity was ~30% of the total activity in the target.