The transport of energy in heated plasmas requires the knowledge of the radiation coefficients. These coefficients consist of contribution of bremsstrahlung, photoionisation, bound-bound transmissions and scattering. Scattering of photons on electrons is taken into account by the model of Thomson, Klein-Nishina and the first order angular momentum of Klein-Nishina. It is shown that radiative scattering becomes an important part of energy transport in high temperature plasmas. Moreover, the contribution of transport correction to scattering is taken into account. The physics is discussed on the example of a heated plutonium plasma at different particle densities and temperatures in radiative equilibrium.
Enhanced Extreme Ultraviolet Emission from Laser-heated Blow-Off Tin Plasmas
Pacific Northwest National Laboratory（太平洋西北国家实验室）；Prism Computational Sciences（棱镜计算科学公司）；Center for Energy Research, University of California San Diego（加州大学圣地亚哥分校能源研究中心）
The energy distributions of Ta ions produced in a nanosecond laser-heated plasma at 4$\times$10$^{15}$ W/cm$^{2}$ are experimentally and theoretically investigated. They are measured far from the target with an electrostatic spectrometer and charge collectors. Shadowgraphy and interferometry are used to characterize the plasma dynamics in the first nanoseconds of the plasma expansion for electron densities ranging from 10$^{18}$ to 10$^{20}$ cm$^{-3}$. The experimental data clearly show two components in the energy distributions which depend on the ion charge states. These components are discu…
A relativistic petawatt laser light can heat heavy metals over keV temperature isochorically and ionize them almost fully. Copious hard X-rays are emitted from the high-Z hot plasma which acts as X-ray sources, while they work as a cooling process of the plasma. The cooling process can affect on the creation of high energy density plasma via the interaction, however, the details are unknown. The X-ray spectrum depends on the plasma temperature, so that it is worthwhile to investigate the radiation cooling effects. We here study the isochoric heating of a solid silver foil irradiated by relativ…
Standard measures of opacity, the imaginary part of the atomic scattering factor $f_2$ and the x-ray mass attenuation coefficient $μ/ρ$, are evaluated in shock-heated boron, boron carbide and boron nitride plasmas. The Hugoniot equation, relating the temperature $T$ behind a shock wave to the compression ratio $ρ/ρ_0$ across the shock front, is used in connection with the plasma equation of state to determine the pressure $p$, effective plasma charge $Z^\ast$ and the K-shell occupation in terms of $ρ/ρ_0$. Solutions of the Hugoniot equation (determined within the framework of the generalized T…
Warm dense matter is a region of phase space that is of high interest to multiple scientific communities ranging from astrophysics to inertial confinement fusion. Further understanding of the conditions and properties of this complex state of matter necessitates experimental benchmarking of the current theoretical models. Benchmarking of transport properties like conductivity and diffusivity has been scarce because they are small and slow processes that require micron-level resolution to see. We discuss development of a radiography platform designed to allow for measurement of these properties…
Hollow toroidal rotation profiles in strongly electron heated H-mode plasmas in the ASDEX Upgrade tokamak
Max Planck Institute for Plasma Physics（马克斯·普朗克等离子体物理研究所）；Department of Applied Physics and Applied Mathematics, Columbia University（哥伦比亚大学应用物理与应用数学系）；VTT（芬兰技术研究中心VTT）
The interaction of supersonic laser-generated plasma jets with a secondary gas target was studied experimentally. The plasma parameters of the jet, and the resulting shock, were characterized using a combination of multi-frame interferometry/shadowgraphy, and X-ray diagnostics, allowing for a detailed study of their structure and evolution. The velocity was obtained with an X-ray streak camera, and filtered X-ray pinhole imaging was used to infer the electron temperature of the jet and shock. The topology of the ambient plasma density was found to have a significant effect on the jet and shock…
An 18-level argon collisional radiative model (CRM) suitable for low pressure was established. The model can be solved by combining the optical emission spectroscopy (OES) with Langmuir probe calibration. In the capacitively coupled plasmas (CCPs) with different frequency and power, the electron temperature and density obtained by the model were compared with those measured by Langmuir probe. It is found that the calibration point at any frequency or power is suitable for the fixed pressure. This method was then applied to the diagnosis of triple-frequency (TF) CCPs, it is shown that the high …
Effects of radio-frequency power and driven frequency on the two-dimensional (axial and radial) distributions of electron density and temperature were experimentally investigated in low pressure capacitively coupled argon plasmas. The intensity profiles of 696.5 nm and 750.4 nm emission lines were detected by employing a spatially resolved diagnostic system, which consists of a charge coupled device (CCD) and bandpass interference filters. The two-dimensional distributions of electron density and electron temperature were calculated from the spatial distributions of emission intensities via a …
Dayside magnetosphere of Mars is a thin layer with usually increased magnetic field and heated planetary ions between the magnetosheath and the ionosphere. The Mars Atmosphere and Volatile Evolution Mission (MAVEN) spacecraft provided, for the first time, high temporal and spatial resolution measurements enabling to study the structure of this region. The region was given several names including the boundary layer, the plasma mantle, and magnetosphere. The outer boundary of this region was called magnetopause, ionopause, ion composition boundary and pile-up boundary (see Espley, 2018). We anal…
Reliable plasma transport modeling for magnetic confinement fusion depends on accurately resolving the ion charge state distribution and radiative power losses of the plasma. These quantities can be obtained from solutions of a collisional-radiative (CR) model at each time step within a plasma transport simulation. However, even compact, approximate CR models can be computationally onerous to evaluate, and in-situ evaluations of these models within a coupled plasma transport code can lead to a rigid bottleneck. A way to bypass this bottleneck is to deploy artificial neural network surrogates f…
Turbulence is a predominant process for energizing electrons and ions in collisionless astrophysical plasmas, and thus is responsible for shaping their radiative signatures (luminosity, spectra, and variability). To better understand the kinetic properties of a collisionless radiative plasma subject to externally driven turbulence, we investigate particle-in-cell simulations of relativistic plasma turbulence with external inverse Compton cooling acting on the electrons. We find that ions continuously heat up while electrons gradually cool down (due to the net effect of radiation), and hence th…
We perform 2D and 3D kinetic simulations of reconnection-mediated turbulent flares in a magnetized electron-positron plasma, with weak and strong radiative cooling. Such flares can be generated around neutron stars and accreting black holes. We focus on the magnetically-dominated regime where tension of the background magnetic field lines exceeds the plasma rest mass by a factor $σ_0 > 1$. In the simulations, turbulence is excited on a macroscopic scale $l_0$, and we observe that it develops by forming thin, dynamic current sheets on various scales. The deposited macroscopic energy dissipates …
High-energy astrophysical systems frequently contain collisionless relativistic plasmas that are heated by turbulent cascades and cooled by emission of radiation. Understanding the nature of this radiative turbulence is a frontier of extreme plasma astrophysics. In this paper, we use particle-in-cell simulations to study the effects of external inverse Compton radiation on turbulence driven in an optically thin, relativistic pair plasma. We focus on the statistical steady state (where injected energy is balanced by radiated energy) and perform a parameter scan spanning from low magnetization t…
The nonthermal particle acceleration during magnetic reconnection remains a fundamental topic in several astrophysical phenomena, such as solar flares, pulsar wind, magnetars, etc, for more than half a century, and one of the unresolved questions is its efficiency. Recently, nonthermal particle acceleration mechanisms during reconnection have been extensively studied by particle-in-cell simulations, yet it is an intriguing enigma as to how the magnetic field energy is divided into thermally heated plasmas and nonthermal particles. Here we study both non-relativistic and relativistic magnetic r…
Collisional-radiative data for tokamak disruption mitigation modeling
Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Curtin University（科廷大学）；Korea Institute of Fusion Energy（韩国聚变能源研究所）；Queensland Quantum and Advanced Technologies Research Institute, Griffith University（格里菲大学昆士兰量子与先进技术研究学院）；School of Environment and Science, Griffith University（格里菲大学环境与科学学院）
We survey the results of a long-term study of the process of radiative recombination. A rigorous theory of nonrelativistic electron radiative recombination with a hydrogen-like ion is used to calculate the total cross section of the process, the effective radiation, the recombination rate coefficient, and the emission coefficient in a plasma with a Maxwellian electron distribution. The exact results are compared with the numerous known asymptotic and interpolation formulas. We propose interpolation formulas which ensure a uniform approximation of all mentioned quantities in a wide range of pla…
Nature's most powerful high-energy sources are capable of accelerating particles to high energy and radiate it away on extremely short timescales, even shorter than the light crossing time of the system. It is yet unclear what physical processes can produce such an efficient acceleration, despite the copious radiative losses. By means of radiative particle-in-cell simulations, we show that magnetically dominated turbulence in pair plasmas subject to strong synchrotron cooling generates a nonthermal particle spectrum with a hard power-law range (slope $p \sim 1$) within a few eddy turnover time…
The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperature-dependent absorption coefficient directly from an oversampled pool of single-…
