Measurements of low-mode asymmetries in the areal density of laser-direct-drive deuterium–tritium cryogenic implosions on OMEGA using neutron spectroscopy

Forrest, C. J.; Crilly, A.; Schwemmlein, A.; Gatu-Johnson, M.; Mannion, O. M.; Appelbe, B.; Betti, R.; Glebov, V. Yu.; Gopalaswamy, V.; Knauer, J. P.; Mohamed, Z. L.; Radha, P. B.; Regan, S. P.; Stoeckl, C.; Theobald, W.

doi:10.1063/5.0101812

Measurements of low-mode asymmetries in the areal density of laser-direct-drive deuterium–tritium cryogenic implosions on OMEGA using neutron spectroscopy

Journal Article · Wed Oct 05 00:00:00 EDT 2022 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/5.0101812· OSTI ID:1900517

^[1]; Crilly, A. ^[2]; Schwemmlein, A. ^[3]; ^[4]; ^[5]; ^[2]; Betti, R. ^[3]; ^[3]; ^[3]; Knauer, J. P. ^[3]; ^[3]; ^[3]; ^[3]; ^[3]; ^[3]

Univ. of Rochester, NY (United States); Laboratory of Energetics, University of Rochester
Imperial College, London (United Kingdom)
Univ. of Rochester, NY (United States)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Areal density is one of the key parameters that determines the confinement time in inertial confinement fusion experiments, and low-mode asymmetries in the compressed fuel are detrimental to the implosion performance. The energy spectra from the scattering of the primary deuterium–tritium (DT) neutrons off the compressed cold fuel assembly are used to investigate low-mode nonuniformities in direct-drive cryogenic DT implosions at the Omega Laser Facility. For spherically symmetric implosions, the shape of the energy spectrum is primarily determined by the elastic and inelastic scattering cross sections for both neutron-deuterium and neutron-tritium kinematic interactions. Two highly collimated lines of sight, which are positioned at nearly orthogonal locations around the OMEGA target chamber, record the neutron time-of-flight signal in the current mode. An evolutionary algorithm is being used to extract a model-independent energy spectrum of the scattered neutrons from the experimental neutron time-of-flight data and is used to infer the modal spatial variations (l = 1) in the areal density. Experimental observations of the low-mode variations of the cold-fuel assembly (ρL₀ + ρL₁) show good agreement with a recently developed model, indicating a departure from the spherical symmetry of the compressed DT fuel assembly. As a result, another key signature that has been observed in the presence of a low-mode variation is the broadening of the kinematic end-point due to the anisotropy of the dense fuel conditions.

View Accepted Manuscript (DOE)

Research Organization:: Univ. of Rochester, NY (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA)

Grant/Contract Number:: NA0003856; NA0003525

OSTI ID:: 1900517

Journal Information:: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 10 Vol. 93; ISSN 0034-6748

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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Deuterium
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Measurements of low-mode asymmetries in the areal density of laser-direct-drive deuterium–tritium cryogenic implosions on OMEGA using neutron spectroscopy

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