First measurements of remaining shell areal density on the OMEGA laser using the Diagnostic for Areal Density (DAD)

Abstract

A glass Cherenkov detector, called the Diagnostic for Areal Density (DAD), has been built and implemented at the OMEGA laser facility for measuring fusion gammas above 430 keV, from which remaining shell ⟨⟩ can be determined. A proof-of-principle experiment is discussed, where signals from a surrogate gas Cherenkov detector are compared with reported values from the wedge range filter and charged particle spectrometer and found to correlate strongly. The design of the more compact port-based DAD diagnostic and results from the commissioning shots are then presented. Once absolutely calibrated, the DAD will be capable of reporting remaining shell ⟨⟩ for plastic and glass capsules within minutes of a shot and with potentially higher precision than existing techniques.

Improved gamma imaging at NIF using the ceramic scintillator GYGAG

“…The gamma system is designed to record 4.4 MeV gammas from the 12 C(n,n ′ γ) 12 C reaction between 14.1 MeV primary neutrons and the remaining high-density carbon (HDC) ablator, which has a strength of 1.1×10 −5 γ/mg/cm 2 /neutron. [16][17][18] There will be an additional signature from the DT gamma, [19][20][21] which is emitted with a strength of (4.6 ± 0.6) ×10 −5 per fusion neutron; however, remaining shell levels at NIF during ICF experiments are in the region of 400 mg/cm 2 , therefore approximately 100× more carbon gammas interact with the scintillator during typical experiments. Original investigations 22 suggested that LYSO would be the ideal candidate for a gamma imaging system at NIF, however, the scintillator could not be manufactured in a large enough single piece (approx.…”

Gamma-based nuclear fusion measurements at inertial confinement fusion facilities

“…The main detectors that are currently in use at ICF facilities and may be used for nuclear astrophysics experiments such as cross-section or S-factor measurements include the two Gas Cherenkov Detectors (GCD's) GCD-1 [10,11] and GCD-3 [12] as well as the Diagnostic for Areal Density (DAD) [13]. There are GCD's available at both the NIF and OMEGA, however, the DAD is only available at OMEGA.…”

“…It is available at OMEGA only. It was originally deployed in 2014 to measure remaining shell areal densities via measurement of 4.4-MeV gammas from the first excited state of carbon [13], but is capable of measuring any gammas above ~0.34 MeV (assuming the standard index of refraction n = 1.46 for fused silica). The DAD consists of 6 mm of tungsten shielding in front of a 6.39-cm diameter, 5-cm thick piece of fused silica, which is directly coupled to a PMT.…”

“…Its solid angle is therefore relatively low. Image originally published in Ref 13. and reproduced with permission from the author and AIP Publishing.…”