In addition, OpSpec is currently used on 18 NIF shots/year, in which both crystals are typically damaged beyond reuse, so efficient production of 36 crystals/year is required. The current elliptical design is an improvement from the convex cylindrical design but has a usable energy range from 900 to 2100 eV. ![]() An elliptically shaped crystal allows an acceptance aperture at the crossover focus between the crystal and the detector, which reduces background and eliminates nearly all reflections from alternate crystal planes. However, with the convex geometry, the low-energy portion of the spectrum suffered from high backgrounds due to scattered x-rays as well as reflections from alternate crystal planes. The original OpSpec used two convex cylindrical crystals for time-integrated measurements of point-projection spectra from 540 to 2100 eV. The soft x-ray Opacity Spectrometer (OpSpec) used on the National Ignition Facility (NIF) has recently incorporated an elliptically shaped crystal. The measurements were taken using selected anodes, filters, and applied voltages to produce well-defined energy lines. A broader range of energies was selected to compare results with previously published data. The absolute response of Agfa D4 x-ray film from 705 to 4620 eV has been measured using the Nevada National Security Site Manson x-ray source. These calibration efforts are vital to the accuracy of the NIF opacity measurements and are conducted in a previously un-studied x-ray energy range under a new film development protocol required by NIF. ![]() The calibration of Agfa D4 x-ray film for use in the OpSpec is communicated here. However, Agfa D4 and D3sc x-ray films’ higher spatial resolution provides increased spectral resolution to the data over the IP-TR image plates, driving the desire for regular use of x-ray film as a detecting medium. The soft x-ray Opacity Spectrometer (OpSpec) fielded at the NIF has an elliptically shaped crystal design that measures x rays in the 900–2100 eV range and currently uses an image plate as the detecting medium. X-ray films remain a key asset for high-resolution x-ray spectral imaging in high-energy-density experiments conducted at the National Ignition Facility (NIF).
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