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...

The Radiochemical Analysis of Gaseous Samples (RAGS) diagnostic apparatus was recently installed at the National Ignition Facility (NIF). Following a NIF shot, RAGS is used to pump the gas load from the NIF chamber for purification and isolation of the noble gases. After collection, the activated gaseous species are counted via gamma spectroscopy for measurement of the capsule areal density and fuel-ablator mix. Collection efficiency was determined by injecting a known amount of (135)Xe into the NIF chamber, which was then collected with RAGS. Commissioning was performed with an exploding pusher capsule filled with isotopically enriched (124)Xe and (126)Xe added to the DT gas fill. Activated xenon species were recovered post-shot and counted via gamma spectroscopy. Results from the collection and commissioning tests are presented. The performance of RAGS allows us to establish a noble gas collection method for measurement of noble gas species produced via neutron and charged particle reactions in a NIF capsule.

The generation of dynamic high energy density plasmas in the pico-to nanosecond time domain at high-energy laser facilities affords unprecedented nuclear science research possibilities. At the National Ignition Facility (NIF), the primary goal of inertial confinement fusion research has led to the synergistic development of a unique high brightness neutron source, sophisticated nuclear diagnostic instrumentation, and versatile experimental platforms. These novel experimental capabilities provide a new path to investigate nuclear processes and structural effects in the time, mass and energy density domains relevant to astrophysical phenomena in a unique terrestrial environment. Some immediate applications include neutron capture cross-section evaluation, fission fragment production, and ion energy loss measurement in

We present the first results from an experimental campaign to measure the atomic ablator-gas mix in the deceleration phase of gas-filled capsule implosions on the National Ignition Facility. Plastic capsules containing CD layers were filled with tritium gas; as the reactants are initially separated, DT fusion yield provides a direct measure of the atomic mix of ablator into the hot spot gas. Capsules were imploded with x rays generated in hohlraums with peak radiation temperatures of ∼294  eV. While the TT fusion reaction probes conditions in the central part (core) of the implosion hot spot, the DT reaction probes a mixed region on the outer part of the hot spot near the ablator-hot-spot interface. Experimental data were used to develop and validate the atomic-mix model used in two-dimensional simulations.

Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α ∼ 3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8 × 10 15 neutrons, with 20% calculated alpha heating at convergence ∼27×. Inertial confinement fusion (ICF) experiments implode millimeter-scale deuterium-tritium (DT) filled spherical capsules, compressing and heating the DT fuel to fusion conditions and releasing energy [1]. Indirect-drive ICF places the fuel-filled capsule at the center of a high-Z radiation enclosure (hohlraum) and strikes the inside walls of the hohlraum with laser power. This produces an internal bath of x rays-a radiation drive which ablates and implodes the fuel-filled capsule. The National Ignition Facility (NIF) [2,3] drives this process using 192 frequency-tripled laser beams (351 nm at 3ω), which enter a cylindrical hohlraum through laser entrance holes (LEHs) at each end. The laser beams are pointed through the LEHs to provide various angles of drive to the capsule such that the superposition of drives can be spherically symmetric throughout the implosion time.Typically, ICF experiments on the NIF have utilized plastic (CH) capsules inside gold hohlraums filled with helium at densities ranging from 0.96 [4] to 1.6 mg=cm Although vacuum hohlraums were initially considered, the long pulse duration for CH capsules led to choosing higher densities of hohlraum fill [7,8] to minimize expansion of the interior gold wall [ Fig. 1(a)] [9]. The intended effect is to maintain an open path for laser propagation to the wall for the full pulse duration.In this Letter, we report on the first experimental campaign on the NIF using near-vacuum hohlraums (NVH) to drive a high convergence cryogenic DT layered capsule implosion. A NVH has a hohlraum fill density of 0.03 mg=cm 3 helium, more than an order of magnitude lower density than conventional gas-filled hohlraums (0.96-1.6 mg=cm 3 ). Symmetry of implosions driven with the NVH is controlled through direct adjustments to the inner and outer beam power balance rather than relying on beam wavelength separations [10] and the resultant crossbeam energy transfer [11,12]. Unlike earlier research on true "vacuum" hohlraums [13][14][15], the NVH...