High Energy Density Physics最新文献

Atomic structure calculations are the first step in an opacity calculation. They provide the self-consistent electronic potential and electron wavefunctions that are needed to evaluate the Slater integrals and dipole matrix elements. In this paper, we show that simple matrix methods can be used to perform Hartree–Fock–Slater or LDA calculations on standard atomic structure grids, including relativistic corrections, yielding bound and continuum wavefunctions that can be used, in conjunction with statistical broadening techniques, to obtain realistic average-atom opacities.

A proposed upgrade to the National Ignition Facility is under consideration that would ultimately increase the maximum operating envelope for the laser to 3.0 MJ with a peak power of 450 TW. This upgrade would provide opportunities to address an expanded set of data needs for NNSA’s Stockpile Stewardship mission, including the potential to generate fusion yields $\ge 30$ megajoules. A simplified model of ignition and burn is used to scope the theoretical maximum target yield as a function of laser driver energy. We examine two indirect drive ICF target designs that make use of the 3 MJ laser drive using a common model for integrated laser-hohlraum simulations. These two designs compare and contrast the impacts of two different ablator materials, pure carbon and CH. Additionally, the potential for increased backscatter from these larger scale designs is discussed.

Motivated by recent experimental results Hartouni et al. (2023); Mannion et al. (2023) which identified the presence of non-Maxwellian ion velocity distributions in ICF plasmas, we revisit the moments method for analysing the shapes of primary neutron spectra emitted by plasmas undergoing thermonuclear burn. We assume that the ion distribution functions are of an arbitrary form and develop a set of “generalized” moments, that are ordered in terms of increasing powers of centre of mass velocity, but for which the effects of shifts of centre of mass velocity (equivalent to fluid velocity in the case of Maxwellian ion distributions) are suppressed. This set of generalized moments provides the most sensitive measure of relative velocity contributions to the shape of the neutron spectrum (an effect that has been colloquially referred to as “viso”). We also demonstrate that pairs of antipodal neutron spectral detectors are most suitable for measuring these contributions.

On December 5th, 2022, controlled fusion ignition was demonstrated for the first time at the National Ignition Facility (NIF), a major achievement in the field of Inertial Confinement Fusion (ICF) requiring a multi-decadal effort involving broad national and international collaborations. To drive the fusion ignition reaction with the compressed fuel capsule, that yielded 3.15 MJ of nuclear energy [1], the NIF laser delivered a high-precision pulse shape with 2.05 MJ of ultra-violet (UV) laser energy and a peak power of 440 TW. This laser energy was an increase of ∼8 % compared to that delivered on the previous “threshold of ignition” record yield experiment (1.37 MJ of yield for 1.89 MJ of laser energy) on August 8th, 2021 [2].

We explain how the results of our extensive research in laser technology and UV optics damage mitigation led to major improvements in the NIF laser, enabling this energy increase along with additional accuracy, precision, and power balance enhancements. Furthermore, we will discuss on-going efforts that have enabled operations at 2.2 MJ of UV energy as well as potential new initiatives to push the laser performance –accuracy and delivered energy– to even higher levels in the future as previously demonstrated on a small subset of NIF beams [3].

We investigate the competition of magnetic reconnections in self-generated and external magnetic fields in laser-produced plasmas. The temporal evolution of plasma structures measured with self-emission imaging shows the vertical expansions and horizontal separation of plasma, which can be signatures of reconnection outflows in self-generated and external magnetic fields, respectively. Because the outflows in self-generated magnetic fields are not clear in the presence of the external magnetic field, the external magnetic field can suppress the magnetic reconnection in self-generated magnetic fields.

In this invited paper, I will touch on some highlights from my research career in the Clarendon Laboratory and in the Central Laser Facility, Rutherford Appleton Laboratory, obtained working in partnership with many outstanding international collaborators. These fall under the three broad themes. The first is novel laser-plasma interactions. The second theme is that of extreme field physics using multi-petawatt laser facilities. The third theme is that of inertial fusion studies. All of these studies indicate that an international, dual-use, 20-MJ Inertial Confinement Fusion (ICF)/Inertial Fusion Energy (IFE) facility, with the first 2-MJ at high repetition rate supplying single-shot high energy amplifiers, will open many new exciting avenues for both fundamental physics and high energy density science in the decades ahead.

Radiography with multiple probe species offers the potential to extract additional information about a given object as compared to radiography with a single probe species. The flexibility for high-power, short-pulse lasers to accelerate a variety of particle species makes laser-driven sources an attractive option to achieve multi-probe radiography. However, crosstalk produced by each of laser-driven source may be responsible for substantial backgrounds on detectors, becoming a significant barrier to achieving simultaneous radiography. In this work, we describe measurements of and mitigation strategies against crosstalk between laser-driven radiography sources in experiments at the OMEGA EP laser.

Rayleigh–Taylor (RT) instabilities are important fluid instabilities that arise in inertial confinement fusion (ICF) capsule implosions, and many other contexts. Multi-mode coupling is observed in experiments and plays a substantial role in material mix from RT instabilities. In this work, we study the evolution of highly multimodal perturbations (power law distribution) that approximate those found at manufactured material interfaces. We use simulations of over 2000 different perturbations in the LANL code xRAGE to identify distinct phases in the processes of bubble growth and bubble merger which can be visualized in a 2D phase portrait with clear regimes of mode growth and decay. Our results show that the dynamic evolution of the instability strongly depends on the mode of the perturbations and mode interactions. The merger process accelerates bubble growth. A non-Markovian region and a transition of the instability from: (1) initial exponential growth to (2) linear growth and to (3) quadratic growth and asymptotic behavior, are clearly captured in the phase space. We have developed a quantitative model of bubble growth that reproduces the dynamic behavior of ensembles of perturbations. Implications for ICF capsules designed for robustness against instabilities are discussed. (LA-UR-23-24496)

The second-order spectral line width formulae from the projection operator and kinetic theory methods were recently compared. It was shown that a systematic expansion of the projection operator width expression including initial correlations formally agrees with the second-order kinetic theory result. It is now shown that the second-order dynamic shifts are also formally the same. The static shifts, however, differ due to an ad hoc treatment of electron-electron correlations in the projection operator method. The approximation is necessary in order to screen the radiator-electron interactions. The differences, however, are expected to be small. The results suggest using the rigorous and more compact second-order width and shift expressions from the kinetic theory method as the starting point for spectral line shape calculations. At line center, however, the projection operator second-order expression for the width and shift simplifies and reduces to the kinetic theory result.

In this study, we investigate the response of linear liquid metal flow to a magnetic field when used as a load for high-repetition pulsed-power discharges and as a sheet for a laser target. When a magnetic field was applied perpendicular to the liquid metal flow, the flow deformed while maintaining its thickness. This approach may reduce current and enhance light sources in Z-pinch and alternative X-pinch discharges. However, low-frequency fluctuations were more prominent when the magnetic field was applied parallel to the liquid metal flow in sheet form. These findings suggest that combining liquid metal flow with a magnetic field could effectively facilitate high-repetition pulsed-power discharges and laser operations.