Kinetics and Mechanism of Ignition in Reactive Al/Ni Nanostructured Materials
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Chemistry↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Effects of New Ab Initio Rate Coefficients on Predictions of Species Formed during n -Butanol Ignition and Pyrolysis
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Karwat, Darshan M. A.↗
Plasma ignition and steady state simulations of the Linac4 H{sup −} ion source
The RF heating of the plasma in the Linac4 H{sup −} ion source has been simulated using a particle-in-cell Monte Carlo collision method. This model is applied to investigate the plasma formation starting from an initial low electron density of 10{sup 12} m{sup −3} and its stabilization at 10{sup 18} m{sup −3}. The plasma discharge at low electron density is driven by the capacitive coupling with the electric field generated by the antenna, and as the electron density increases the capacitive electric field is shielded by the plasma and induction drives the plasma heating process. Plasma properties such as e{sup −}/ion densities and energies, sheath formation, and shielding effect are presented and provide insight to the plasma properties of the hydrogen plasma.
43 PARTICLE ACCELERATORS↗
Metrics for long wavelength asymmetries in inertial confinement fusion implosions on the National Ignition Facility
We investigate yield degradation due to applied low mode P2 and P4 asymmetries in layered inertial confinement fusion implosions. This study has been performed with a large database of >600 2D simulations. We show that low mode radiation induced drive asymmetries can result in significant deviation between the core hot spot shape and the fuel ρR shape at peak compression. In addition, we show that significant residual kinetic energy at peak compression can be induced by these low mode asymmetries. We have developed a metric, which is a function of the hot spot shape, fuel ρR shape, and residual kinetic energy at peak compression, that is well correlated to yield degradation due to low mode shape perturbations. It is shown that the ρR shape and residual kinetic energy cannot, in general, be recovered by inducing counter asymmetries to make the hot core emission symmetric. In addition, we show that the yield degradation due to low mode asymmetries is well correlated to measurements of time dependent shape throughout the entire implosion, including early time shock symmetry and inflight fuel symmetry.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Recent performance and ignition tests of the pulsed SNS H{sup −} source for 1-MW neutron production
After acquiring several reliable spare targets, SNS ramped the beam power from 850 kW to 1.4 MW, which required an increase in H{sup −} beam pulse length from 0.88 to 1.0 ms at 60 Hz. This increase initially produced slow 2-MHz power ramp-ups and, after several weeks of uninterrupted operation, it produced plasma outages every time the pulse length was raised above ∼0.95 ms. Similar outages were previously observed towards the end of long service cycles, which were believed to indicate that the breakdown voltage of the high purity hydrogen started to exceed the induced electric fields. In 2011 the RF was reconfigured to start with 10 cycles of 1.96 MHz, which yielded the shortest H{sup −} beam rise times and apparently eliminated those plasma outages. The new, pulse-length dependent outages were eliminated by increasing the initial frequency to 1.985 MHz. However, careful frequency studies are unable to justify this frequency. In addition, the paper discusses the issues and solutions for the electron-dump voltage, which starts to sag and become unstable after several weeks of high current operation. At the request of the authors and the Proceedings Editor this article has been updated to include References 3–13, which were present in the author’s original submission but were lost during manuscript processing in the Proceedings Editor's office. The updated article was published on 5 May 2015.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Advances in x-ray framing cameras at the National Ignition Facility to improve quantitative precision in x-ray imaging
We describe an experimental method to measure the gate profile of an x-ray framing camera and to determine several important functional parameters: relative gain (between strips), relative gain droop (within each strip), gate propagation velocity, gate width, and actual inter-strip timing. Several of these parameters cannot be measured accurately by any other technique. This method is then used to document cross talk-induced gain variations and artifacts created by radiation that arrives before the framing camera is actively amplifying x-rays. Electromagnetic cross talk can cause relative gains to vary significantly as inter-strip timing is varied. This imposes a stringent requirement for gain calibration. If radiation arrives before a framing camera is triggered, it can cause an artifact that manifests as a high-intensity, spatially varying background signal. Furthermore, we have developed a device that can be added to the framing camera head to prevent these artifacts.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Embedded fiber Bragg grating pressure measurement during thermal ignition of a high explosive
A high-speed fiber Bragg grating based pressure-only measurement is reported for the high explosive PBXN-9 under thermal initiation conditions. During exothermic thermal runaway, an explosion rise time of 500 μs reaching a peak pressure of 660 MPa is measured. Lastly, the approach offers a direct measure pressure diagnostic useful for quantifying reaction violence for high explosive chemistry.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Ignition and Growth Modeling of Detonation Reaction Zone Experiments on Single Crystals of PETN and HMX
Abstract not provided
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ignition and Growth Reactive Flow Modeling of Recent HMX/TATB Detonation Experiments
Abstract not provided
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Examining the radiation drive asymmetries present in the high foot series of implosion experiments at the National Ignition Facility
This paper details and examines the origins of radiation drive asymmetries present during the initial High Foot implosion experiments. Such asymmetries are expected to reduce the stagnation pressure and the resulting yield of these experiments by several times. Analysis of reemission and dual axis shock timing experiments indicates that a flux asymmetry, with a P2/P0 amplitude that varies from -10 to -5 %, is present during the first shock of the implosion. This first shock asymmetry can be corrected through adjustments to the laser cone fraction. A thin shell model and more detailed radiation hydrodynamic calculations indicate that an additional negative P2/P0 asymmetry during the second or portions of the third shock is required to reach the observed amount of asymmetry in the shape of the ablator at peak implosion velocity. In conjunction with symmetry data from the x-ray self emission produced at stagnation, these models also indicate that after the initially negative P2/P0 flux asymmetry, the capsule experiences a positive P2/P0 flux asymmetry that develops at or before ~2 ns into the peak of the laser power. Here, direct evidence for this inference, using measurements of the x-ray emission produced by the lasers irradiating the hohlraum, is presented. This data indicates that the reduction in the transmitted inner laser cone energy results from impeded propagation through the plasma associated with the ablation of the capsule target. This paper also correlates measurements of the outer cone laser deposition location with variations in the observed x-ray self emission shape from experiments conducted with nominally the same input conditions.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Enhanced hot-electron production and strong-shock generation in hydrogen-rich ablators for shock ignition
Experiments were performed with CH, Be, C, and SiO 2 ablators interacting with high-intensity UV laser radiation (5 × 10 15 W/cm 2 , λ = 351 nm) to determine the optimum material for hot-electron production and strong-shock generation. Significantly more hot electrons are produced in CH (up to ~13% instantaneous conversion efficiency), while the amount is a factor of ~2 to 3 lower in the other ablators. A larger hot-electron fraction is correlated with a higher effective ablation pressure. As a result, the higher conversion efficiency in CH is attributed to stronger damping of ion-acoustic waves because of the presence of light H ions.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
On krypton-doped capsule implosion experiments at the National Ignition Facility
Not Available
Chen, Hui↗
Development of high intensity X-ray sources at the National Ignition Facility
Laser heated plasmas have provided recently some of the most powerful and energetic nanosecond length laboratory sources of x-ray photons (E photon = 1–30 keV). The highest x-ray to laser conversion is currently accessible by using underdense (n e ~ 0.25 n c ) plasmas since optimal laser coupling is obtained in millimeter scale targets. The targets can have conversion efficiencies of up to 10%. Furthermore, several types of targets can be used to produce underdense plasmas: metal lined cylindrical cavities, gas pipes, and most recently nano-wire foams. Both the experimental and simulation details of these high intensity x-ray sources are discussed.
74 ATOMIC AND MOLECULAR PHYSICS↗