The first measurements of soft x-ray flux from ignition scale Hohlraums at the National Ignition Facility using DANTE (invited)

Abstract

The first 96 and 192 beam vacuum Hohlraum target experiments have been fielded at the National Ignition Facility demonstrating radiation temperatures up to 340 eV and fluxes of 20 TW/sr as viewed by DANTE representing an ∼20 times flux increase over NOVA/Omega scale Hohlraums. The vacuum Hohlraums were irradiated with 2 ns square laser pulses with energies between 150 and 635 kJ. They produced nearly Planckian spectra with about 30±10% more flux than predicted by the preshot radiation hydrodynamic simulations. To validate these results, careful verification of all component calibrations, cable deconvolution, and software analysis routines has been conducted. In addition, a half Hohlraum experiment was conducted using a single 2 ns long axial quad with an irradiance of ∼2×10(15) W/cm(2) for comparison with NIF Early Light experiments completed in 2004. We have also completed a conversion efficiency test using a 128-beam nearly uniformly illuminated gold sphere with intensities kept low (at 1×10(14) W/cm(2) over 5 ns) to avoid sensitivity to modeling uncertainties for nonlocal heat conduction and nonlinear absorption mechanisms, to compare with similar intensity, 3 ns OMEGA sphere results. The 2004 and 2009 NIF half-Hohlraums agreed to 10% in flux, but more importantly, the 2006 OMEGA Au Sphere, the 2009 NIF Au sphere, and the calculated Au conversion efficiency agree to ±5% in flux, which is estimated to be the absolute calibration accuracy of the DANTEs. Hence we conclude that the 30±10% higher than expected radiation fluxes from the 96 and 192 beam vacuum Hohlraums are attributable to differences in physics of the larger Hohlraums.

Capsule implosion optimization during the indirect-drive National Ignition Campaign

“…The NEL drive results in turn matched modeling validated by prior similar energy Nova 31 and OMEGA 32 facility hohlraum data 33 taken with the same type of Dante detector itself shown to agree 34 with the analogous soft x-ray power diagnostic for the LMJ facility, 35 DMX. 36 This x-ray drive consistency across facilities 37 has lent further credence to an observed improvement 38 in x-ray CE at fixed laser intensity as vacuum hohlraum scale is increased on NIF, attributed to increased volume-to-surface area ratio. Finally, gas-filled hohlraums 39,40 and tubes 41 demonstrated the efficacy of laser spot smoothing in improving radiation drive and beam propagation using phase plates, 42 polarization smoothing 43 (PS), and smoothing by spectral dispersion (SSD) for both the cases of a NIF quad geometry and the NIF-like multicone OMEGA geometry.…”

Spectroscopic characterisation of the effects of plasma geometry on the angular distribution of X-Ray emission in HED plasmas

“…The absolute combined response function of each channel, as well as its uncertainty are known and characterised. This allows for absolute measurements of the X-ray emission which are commonly used by experimentalists to calculate the radiation temperature in ICF related experiments [123,124]. Recently, it was shown that a priori information can be introduced in this analysis to elliminate the assumption of a Planckian radiation field, which produces more accurate results [125].…”

Iron X-ray Transmission at Temperature Near 150 eV Using the National Ignition Facility: First Measurements and Paths to Uncertainty Reduction

“…Sample temperature in the NIF experiment can be evaluated in two ways. Figure 1 (right) showed the diagnostic view of an absolutely calibrated X-ray flux diagnostic (DANTE-2) [19][20][21][22], which measured an effective brightness temperature of around 140-150 eV during the time of the X-ray transmission measurement (4.3 ns) for the NIF shot discussed in this paper. The X-ray transmission measurement time itself is measured separately, after time-of-flight corrections, from the capsule backlighter's X-ray flash observed using the other flux diagnostic (DANTE-1).…”