Operations on the National Ignition Facility

Wonterghem, B. M. Van; Brereton, S.J.; Burr, R. F.; Folta, P.; L., Hardy, D.; Jize, Nicholas N.; Kohut, T.; Land, T. A.; Merritt, B.T.

doi:10.13182/fst15-118

Cited by 31 publications

(19 citation statements)

References 7 publications

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“…At the National Ignition Facility (NIF) [1], cryogenically layered capsules of deuterium (D) and tritium (T) fuel contained in 2-mm-diam carbon-based shells are imploded through laser irradiation of a surrounding high-Z hohlraum [2,3]. The imploding DT fuel assembles and "stagnates" in a configuration with a cold high-density shell surrounding a low-density hot spot.…”

mentioning

confidence: 99%

Indications of flow near maximum compression in layered deuterium-tritium implosions at the National Ignition Facility

Johnson¹,

Knauer²,

Cerjan³

et al. 2016

Phys. Rev. E

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An accurate understanding of burn dynamics in implosions of cryogenically layered deuterium (D) and tritium (T) filled capsules, obtained partly through precision diagnosis of these experiments, is essential for assessing the impediments to achieving ignition at the National Ignition Facility. We present measurements of neutrons from such implosions. The apparent ion temperatures T ion are inferred from the variance of the primary neutron spectrum. Consistently higher DT than DD T ion are observed and the difference is seen to increase with increasing apparent DT T ion . The line-of-sight rms variations of both DD and DT T ion are small, ∼150 eV, indicating an isotropic source. The DD neutron yields are consistently high relative to the DT neutron yields given the observed T ion . Spatial and temporal variations of the DT temperature and density, DD-DT differential attenuation in the surrounding DT fuel, and fluid motion variations contribute to a DT T ion greater than the DD T ion , but are in a one-dimensional model insufficient to explain the data. We hypothesize that in a three-dimensional interpretation, these effects combined could explain the results. DOI: 10.1103/PhysRevE.94.021202 At the National Ignition Facility (NIF) [1], cryogenically layered capsules of deuterium (D) and tritium (T) fuel contained in 2-mm-diam carbon-based shells are imploded through laser irradiation of a surrounding high-Z hohlraum [2,3]. The imploding DT fuel assembles and "stagnates" in a configuration with a cold high-density shell surrounding a low-density hot spot. Efficient conversion of shell kinetic energy to hot-spot thermal energy is an essential requirement to achieving ignition at the NIF [4,5]. At peak convergence, this ideally results in a spherically symmetric, cold, dense DT fuel shell with an areal density ρR of ∼1.5 g/cm 2 surrounding a ∼5-keV hot spot with ρR ∼ 0.3 g/cm 2 . Although the word "stagnation" is often used for this phase of the implosion, it is inappropriate as the DT and DD neutron spectra indicate significant remaining kinetic energy. Neutron spectrometers [6][7][8][9][10][11][12][13][14][15] provide directional measurements of DT and DD neutron spectra from which yield, burn-averaged ion temperatures T ion and areal densities ρR are obtained. Neutron activation detectors (NADs) [16] measure the unscattered DT yield Y DT . In this paper we focus on the ion "temperatures" from a more extensive set of experiments than previously published [2] and conclude that the fuel assembly during burn in layered DT implosions is not well described by detailed one-dimensional (1D) physics models and simulations. The leading hypothesis for the observed discrepancy between the data and the 1D description is significant disordered motion and the highly 3D nature of the assembly at burn.For a homogeneous stationary DT plasma in thermal equilibrium at ion temperature T thermal , the variance of the * Corresponding author: gatu@psfc.mit.edu DT neutron spectrum (in units of neutron energy) is given bywhere E n is th...

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confidence: 99%

Indications of flow near maximum compression in layered deuterium-tritium implosions at the National Ignition Facility

Johnson¹,

Knauer²,

Cerjan³

et al. 2016

Phys. Rev. E

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“…9) and areal densities (R) up to ~1.3 g/cm 2 (Ref. 10; corresponding to densities ranging from many tens of g/cm 3 in the center of the implosion to many hundreds of g/cm 3 in the surrounding dense fuel layer) have been demonstrated.…”

Section: Imentioning

confidence: 99%

“…INTRODUCTION Thermonuclear reactions relevant to stellar nucleosynthesis (SN) and big-bang nucleosynthesis (BBN) have been explored traditionally by means of accelerator experiments. 1 High-energy-density (HED) plasmas generated in inertial confinement fusion (ICF) experiments at large lasers such as OMEGA 2 and the National Ignition Facility (NIF) 3,4 more closely mimic an astrophysical environment in several ways. The target nuclei in accelerator experiments are surrounded by bound electrons, while electrons occupy mainly continuum states in stars and in HED plasmas.…”

Section: Imentioning

confidence: 99%

“…(b) Reactivities for SN and BBN-relevant reactions are generally low and decrease rapidly with decreasing temperature. Here, as an example, BBN-relevant reactions T( 3 He,d) and 3 He(,) 7 Be are shown in green, proton-proton-chain-relevant reactions D(p,) 3 He and 3 He( 3 He,2p) in black, CNO-relevant reactions 15 N(p,) 12 C and 14 N(p,) 15 O in blue, and reference reactions D(T,n), D(D,n) 3 He, D( 3 He,p) and T(T,2n) in red.…”

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confidence: 99%

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Development of an inertial confinement fusion platform to study charged-particle-producing nuclear reactions relevant to nuclear astrophysics

et al. 2017

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This paper describes the development of a platform to study astrophysically relevant nuclear reactions using inertial-confinement fusion implosions on the OMEGA and National Ignition Facility laser facilities, with a particular focus on optimizing the implosions to study charged-particle-producing reactions. Primary requirements on the platform are high yield, for high statistics in the fusion product measurements, combined with low areal density, to allow the charged fusion products to escape. This is optimally achieved with direct-drive exploding pusher implosions using thin-glass-shell capsules. Mitigation strategies to eliminate a possible target sheath potential which would accelerate the emitted ions are discussed. The potential impact of kinetic effects on the implosions is also considered. The platform is initially employed to study the complementary T(t,2n)α, T(3He,np)α and 3He(3He,2p)α reactions. Proof-of-principle results from the first experiments demonstrating the ability to accurately measure the energy and yields of charged particles are presented. Lessons learned from these experiments will be used in studies of other reactions. The goals are to explore thermonuclear reaction rates and fundamental nuclear physics in stellar-like plasma environments, and to push this new frontier of nuclear astrophysics into unique regimes not reachable through existing platforms, with thermal ion velocity distributions, plasma screening, and low reactant energies.

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“…Together, the recent increase in yields at OMEGA and the renewed interest in precision T ion measurements motivated the present study, which is aimed at (i) evaluating achievable T ion measurement quality with the current MRS and (ii) identifying steps toward further improving this measurement. Note that a similar MRS installed on the National Ignition Facility 20 has been reporting T ion since 2011, 21 recently with significantly improved precision. 22 T ion on OMEGA is currently only measured using nTOF detectors, and complementary highprecision measurements using a different technique would be very valuable.…”

Section: Introductionmentioning

confidence: 99%

Measurement of apparent ion temperature using the magnetic recoil spectrometer at the OMEGA laser facility

Johnson

Katz

Forrest

et al. 2018

Review of Scientific Instruments

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The Magnetic Recoil neutron Spectrometer (MRS) at the OMEGA laser facility has been routinely used to measure deuterium-tritium (DT) yield and areal density in cryogenically layered implosions since 2008. Recently, operation of the OMEGA MRS in higher-resolution mode with a new smaller, thinner (4 cm 2 , 57 µm thick) CD 2 conversion foil has also enabled inference of the apparent DT ion temperature (T ion) from MRS data. MRS-inferred T ion compares well with T ion as measured using neutron time-of-flight spectrometers, which is important as it demonstrates good understanding of the very different systematics associated with the two independent measurements. The MRS resolution in this configuration, ∆E MRS = 0.91 MeV FWHM, is still higher than that required for a high-precision T ion measurement. We show how fielding a smaller foil closer to the target chamber center and redesigning the MRS detector array could bring the resolution to ∆E MRS = 0.45 MeV, reducing the systematic T ion uncertainty by more than a factor of 4.

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Operations on the National Ignition Facility

Cited by 31 publications

References 7 publications

Indications of flow near maximum compression in layered deuterium-tritium implosions at the National Ignition Facility

Indications of flow near maximum compression in layered deuterium-tritium implosions at the National Ignition Facility

Development of an inertial confinement fusion platform to study charged-particle-producing nuclear reactions relevant to nuclear astrophysics

Measurement of apparent ion temperature using the magnetic recoil spectrometer at the OMEGA laser facility

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