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Rinderknecht, H.

Publications and source records attributed to Rinderknecht, H..

14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Experimental Validation of Low- Z Ion-Stopping Formalisms around the Bragg Peak in High-Energy-Density Plasmas

Here, we report on the first accurate validation of low-$Z$ ion-stopping formalisms in the regime ranging from low-velocity ion stopping—through the Bragg peak—to high-velocity ion stopping in well-characterized high-energy-density plasmas. These measurements were executed at electron temperatures and number densities in the range of 1.4–2.8 keV and 4 × 10 23 –8 × 10 23 cm –3 , respectively. For these conditions, it is experimentally demonstrated that the Brown-Preston-Singleton formalism provides a better description of the ion stopping than other formalisms around the Bragg peak, except for the ion stopping at v i ~0.3 v th , where the Brown-Preston-Singleton formalism significantly underpredicts the observation. It is postulated that the inclusion of nuclear-elastic scattering, and possibly coupled modes of the plasma ions, in the modeling of the ion-ion interaction may explain the discrepancy of ~20% at this velocity, which would have an impact on our understanding of the alpha energy deposition and heating of the fuel ions, and thus reduce the ignition threshold in an ignition experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

A 3D dynamic model to assess the impacts of low-mode asymmetry, aneurysms and mix-induced radiative loss on capsule performance across inertial confinement fusion platforms

A simple 3D dynamic model for inertial confinement fusion (ICF) implosions has been developed and used to assess the impacts of low-mode asymmetry, aneurysms and mix-induced radiative loss on capsule performance across ICF platforms. While benchmarked against radiation hydrodynamics simulations, this model benefits from simplicity and speed to allow rapid assessment of possible sources of degradation as well as to help build intuition about the relative importance of different effects. Degradations in the model result from 3D pr areal density perturbations that grow under deceleration from a radial stagnation flow, resulting in reduced convergence, stagnation pressure and temperature. When available, experimental data are used as input to seed 3D perturbations in the model so that the actual observed hotspot and shell areal density asymmetry at stagnation, as well as the radiation loss increase from mix impurities, are accurately reproduced. This model is applied to a broad set of implosion data from the NIF and Omega, including examples from both indirect drive and direct drive. The model matches most experimental observables and explains major performance degradation mechanisms which can result in 30–100-fold reductions in yield. We investigate a modified ignition criterion that accounts for the increase in expansion pdV work, due to the presence of 3D pr perturbations and loss-of-confinement in thin regions of the shell.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Experimental Validation of Low-Z Ion-Stopping Formalisms Around the Bragg Peak in High-Energy-Density Plasmas

We report on the first accurate validation of low-Z ion-stopping formalisms in the regime ranging from low-velocity ion stopping – through the Bragg peak – to high-velocity ion stopping in well-characterized High-Energy-Density Plasmas. These measurements were executed at electron temperatures and number densities in the range of 1.4 – 2.8 keV and 4x10^23 – 8x10^23 cm^-3, respectively. For these conditions, it is experimentally demonstrated that the Brown-Preston-Singleton formalism provides a better description of the ion stopping than other formalisms around the Bragg peak, except for the ion stopping at vi ~ 0.3vth, where the Brown-Preston-Singleton formalism significantly under predicts the observation. It is postulated that the inclusion of nuclear-elastic scattering and possibly non-thermal velocity distributions, due to the Knudsen reduction of the high-velocity tail, in the modeling of the ion-ion interaction may explain the discrepancy of ~20% at this velocity, which would have an impact on our understanding of the alpha energy deposition and heating of the fuel ions, and thus reduce the ignition threshold in an ignition experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

FY17 LLNL Omega Experimental Programs

The Capseed campaign goal is to measure shock front velocity non-uniformities in Inertial Confinement Fusion (ICF) ablator materials and quantify the level of non-uniformity caused by intrinsic effects. This is done using the Omega High Resolution Velocimeter (OHRV) to obtain velocity maps of the optically reflecting shock front following release of the ablator material into either PMMA for the warm experiments or cryogenic deuterium for the cryo experiments. For the three half-days in FY17 the focus was twofold: complete measurements on the impact of oxygen heterogeneity and oxygen mitigation layers for glow discharge polymer (GDP), and begin measuring velocity non-uniformities on deep release from Be, GDP, and highdensity carbon (HDC) into D2 with improved velocity sensitivity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

FY16 LLNL Omega Experimental Programs

In FY16, LLNL’s High-Energy-Density Physics (HED) and Indirect Drive Inertial Confinement Fusion (ICF-ID) programs conducted several campaigns on the OMEGA laser system and on the EP laser system, as well as campaigns that used the OMEGA and EP beams jointly. Overall, these LLNL programs led 430 target shots in FY16, with 304 shots using just the OMEGA laser system, and 126 shots using just the EP laser system. Approximately 21% of the total number of shots (77 OMEGA shots and 14 EP shots) supported the Indirect Drive Inertial Confinement Fusion Campaign (ICF-ID). The remaining 79% (227 OMEGA shots and 112 EP shots) were dedicated to experiments for High-Energy-Density Physics (HED). Highlights of the various HED and ICF campaigns are summarized in the following reports. In addition to these experiments, LLNL Principal Investigators led a variety of Laboratory Basic Science campaigns using OMEGA and EP, including 81 target shots using just OMEGA and 42 shots using just EP. The highlights of these are also summarized, following the ICF and HED campaigns. Overall, LLNL PIs led a total of 553 shots at LLE in FY 2016. In addition, LLNL PIs also supported 57 NLUF shots on Omega and 31 NLUF shots on EP, in collaboration with the academic community.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

The near vacuum hohlraum campaign at the NIF: A new approach

The near vacuum campaign on the National Ignition Facility has concentrated its efforts over the last year on finding the optimum target geometry to drive a symmetric implosion at high convergence ratio (30x). As the hohlraum walls are not tamped with gas, the hohlraum is filling with gold plasma and the challenge resides in depositing enough energy in the hohlraum before it fills up. Hohlraum filling is believed to cause symmetry swings late in the pulse that are detrimental to the symmetry of the hot spot at high convergence. This paper describes a series of experiments carried out to examine the effect of increasing the distance between the hohlraum wall and the capsule (case to capsule ratio) on the symmetry of the hot spot. These experiments have shown that smaller Case to Capsule Ratio (CCR of 2.87 and 3.1) resulted in oblate implosions that could not be tuned round. Larger CCR (3.4) led to a prolate implosion at convergence 30x implying that inner beam propagation at large CCR is not impeded by the expanding hohlraum plasma. A Case to Capsule ratio of 3.4 is a promising geometry to design a round implosion but in a smaller hohlraum where the hohlraum losses are lower, enabling a wider cone fraction range to adjust symmetry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Observation of a Reflected Shock in an Indirectly Driven Spherical Implosion at the National Ignition Facility

A 200 μm radius hot spot at more than 2 keV temperature, 1 g=cm3 density has been achieved on the National Ignition Facility using a near vacuum hohlraum. The implosion exhibits ideal one-dimensional behavior and 99% laser-to-hohlraum coupling. The low opacity of the remaining shell at bang time allows for a measurement of the x-ray emission of the reflected central shock in a deuterium plasma. Comparison with 1D hydrodynamic simulations puts constraints on electron-ion collisions and heat conduction. Results are consistent with classical (Spitzer-Harm) heat flux.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

High-density carbon ablator experiments on the National Ignition Facility

High Density Carbon (HDC) is a leading candidate as an ablator material for Inertial Confinement Fusion (ICF) capsules in x-ray (indirect) drive implosions. HDC has a higher density (3.5 g/cc) than plastic (CH, 1 g/cc), which results in a thinner ablator with a larger inner radius for a given capsule scale. This leads to higher x-ray absorption and shorter laser pulses compared to equivalent CH designs. This paper will describe a series of experiments carried out to examine the feasibility of using HDC as an ablator using both gas filled hohlraums and lower density, near vacuum hohlraums. These experiments have shown that deuterium (DD) and deuterium-tritium gas filled HDC capsules driven by a hohlraum filled with 1.2 mg/cc He gas, produce neutron yields a factor of 2× higher than equivalent CH implosions, representing better than 50% Yield-over-Clean (YoC). In a near vacuum hohlraum (He = 0.03 mg/cc) with 98% laser-to-hohlraum coupling, such a DD gas-filled capsule performed near 1D expectations. A cryogenic layered implosion version was consistent with a fuel velocity = 410 ± 20 km/s with no observed ablator mixing into the hot spot.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2014

Species separation and kinetic effects in collisional plasma shocks

The properties of collisional shock waves propagating in uniform plasmas are studied with ion-kinetic calculations, in both slab and spherical geometry and for the case of one and two ion species. Despite the presence of an electric field at the shock front—and in contrast to the case where an interface is initially present [C. Bellei et al., Phys. Plasmas 20, 044702 (2013)]—essentially no ion reflection at the shock front is observed due to collisions, with a probability of reflection ≲10 -4 for the cases presented. A kinetic two-ion-species spherical convergent shock is studied in detail and compared against an average-species calculation, confirming effects of species separation and differential heating of the ion species at the shock front. The effect of different ion temperatures on the DT and D3He fusion reactivity is discussed in the fluid limit and is estimated to be moderately important.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Structure and Dynamics of Colliding Plasma Jets

Monoenergetic-proton radiographs of laser-generated, high-Mach-number plasma jets colliding at various angles shed light on the structures and dynamics of these collisions. The observations compare favorably with results from 2D hydrodynamic simulations of multistream plasma jets, and also with results from an analytic treatment of electron flow and magnetic field advection. In collisions of two noncollinear jets, the observed flow structure is similar to the analytic model’s prediction of a characteristic feature with a narrow structure pointing in one direction and a much thicker one pointing in the opposite direction. Spontaneous magnetic fields, largely azimuthal around the colliding jets and generated by the well-known ∇T e ×∇n e Biermann battery effect near the periphery of the laser spots, are demonstrated to be “frozen in” the plasma (due to high magnetic Reynolds number R M ~5×10⁴) and advected along the jet streamlines of the electron flow. These studies provide novel insight into the interactions and dynamics of colliding plasma jets.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

FY13 LLNL OMEGA Experimental Programs

In FY13, LLNL’s High-Energy-Density Physics (HED) and Indirect Drive Inertial Confinement Fusion (ICF-ID) programs conducted several campaigns on the OMEGA laser system and on the EP laser system, as well as campaigns that used the OMEGA and EP beams jointly. Overall LLNL led 290 target shots involving the OMEGA laser system and 158 target shots involving the EP laser system. Approximately 34% of the total number of shots (93 OMEGA shots, 58 EP shots) shots supported the Indirect Drive Inertial Confinement Fusion Campaign (ICF-ID). The remaining 66% (197 OMEGA shots and 100 EP shots) were dedicated to experiments for High-Energy-Density Physics (HED).

36 MATERIALS SCIENCE↗