Engineering topics

Wan, A.

Publications and source records attributed to Wan, A..

10 records

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 OSTI2017

The role of hot spot mix in the low-foot and high-foot implosions on the NIF

Hydrodynamic mix of the ablator into the DT fuel layer and hot spot can be a critical performance limitation in inertial confinement fusion implosions. This mix results in increased radiation loss, cooling of the hot spot, and reduced neutron yield. To quantify the level of mix, we have developed a simple model that infers the level of contamination using the ratio of the measured x-ray emission to the neutron yield. The principal source for the performance limitation of the “low-foot” class of implosions appears to have been mix. As a result, lower convergence “high-foot” implosions are found to be less susceptible to mix, allowing velocities of >380 km/s to be achieved.

42 ENGINEERING↗

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

Inertially confined fusion plasmas dominated by alpha-particle self-heating [Alpha-particle self-heating dominated inertially confined fusion plasmas]

Alpha-particle self-heating, the process of deuterium–tritium fusion reaction products depositing their kinetic energy locally within a fusion reaction region and thus increasing the temperature in the reacting region, is essential for achieving ignition in a fusion system. Here, we report new inertial confinement fusion experiments where the alpha-particle heating of the plasma is dominant with the fusion yield produced exceeding the fusion yield from the work done on the fuel (pressure times volume change) by a factor of two or more. These experiments have achieved the highest yield (26 ± 0.5 kJ) and stagnation pressures ( &#8781 220 ± 40 Gbar) of any facility-based inertial confinement fusion experiments, although they are still short of the pressures required for ignition on the National Ignition Facility (~300–400 Gbar). Finally, these experiments put us in a new part of parameter space that has not been extensively studied so far because it lies between the no-alpha-particle-deposition regime and ignition.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

FY15 LLNL OMEGA Experimental Programs

In FY15, 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 468 target shots in FY15, with 315 shots using just the OMEGA laser system, 145 shots using just the EP laser system, and 8 Joint shots using Omega and EP together. Approximately 25% of the total number of shots (56 OMEGA shots and 67 EP shots, including the 8 Joint shots) supported the Indirect Drive Inertial Confinement Fusion Campaign (ICF-ID). The remaining 75% (267 OMEGA shots and 86 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.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Demonstration of High Performance in Layered Deuterium-Tritium Capsule Implosions in Uranium Hohlraums at the National Ignition Facility

We report on the first layered deuterium-tritium (DT) capsule implosions indirectly driven by a “highfoot” laser pulse that were fielded in depleted uranium hohlraums at the National Ignition Facility. Recently, high-foot implosions have demonstrated improved resistance to ablation-front Rayleigh-Taylor instability induced mixing of ablator material into the DT hot spot [Hurricane et al., Nature (London) 506, 343 (2014)]. Uranium hohlraums provide a higher albedo and thus an increased drive equivalent to an additional 25 TW laser power at the peak of the drive compared to standard gold hohlraums leading to higher implosion velocity. Additionally, we observe an improved hot-spot shape closer to round which indicates enhanced drive from the waist. In contrast to findings in the National Ignition Campaign, now all of our highest performing experiments have been done in uranium hohlraums and achieved total yields approaching 10 16 neutrons where more than 50% of the yield was due to additional heating of alpha particles stopping in the DT fuel.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

Thin Shell, High Velocity Inertial Confinement Fusion Implosions on the National Ignition Facility

Experiments have recently been conducted at the National Ignition Facility utilizing inertial confinement fusion capsule ablators that are 175 and 165 μm in thickness, 10% and 15% thinner, respectively, than the nominal thickness capsule used throughout the high foot and most of the National Ignition Campaign. These three-shock, high-adiabat, high-foot implosions have demonstrated good performance, with higher velocity and better symmetry control at lower laser powers and energies than their nominal thickness ablator counterparts. Little to no hydrodynamic mix into the DT hot spot has been observed despite the higher velocities and reduced depth for possible instability feedthrough. Earlier results have shown good repeatability, with up to 1/2 the neutron yield coming from α-particle self-heating.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

FY14 LLNL OMEGA Experimental Programs

In FY14, 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 324 target shots in FY14, with 246 shots using just the OMEGA laser system, 62 shots using just the EP laser system, and 16 Joint shots using Omega and EP together. Approximately 31% of the total number of shots (62 OMEGA shots, 42 EP shots) shots supported the Indirect Drive Inertial Confinement Fusion Campaign (ICF-ID). The remaining 69% (200 OMEGA shots and 36 EP shots, including the 16 Joint 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.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Atomic state and characterization of nitrogen at the SiC/SiO{sub 2} interface

We report on the concentration, chemical bonding, and etching behavior of N at the SiC(0001)/SiO{sub 2} interface using photoemission, ion scattering, and computational modeling. For standard NO processing of a SiC MOSFET, a sub-monolayer of nitrogen is found in a thin inter-layer between the substrate and the gate oxide (SiO{sub 2}). Photoemission shows one main nitrogen related core-level peak with two broad, higher energy satellites. Comparison to theory indicates that the main peak is assigned to nitrogen bound with three silicon neighbors, with second nearest neighbors including carbon, nitrogen, and oxygen atoms. Surprisingly, N remains at the surface after the oxide was completely etched by a buffered HF solution. This is in striking contrast to the behavior of Si(100) undergoing the same etching process. We conclude that N is bound directly to the substrate SiC, or incorporated within the first layers of SiC, as opposed to bonding within the oxide network. These observations provide insights into the chemistry and function of N as an interface passivating additive in SiC MOSFETs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

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↗