David Salzmann

X-ray astronomy in the laboratory with a miniature compact object produced by laser-driven implosion

It has been suggested that the extreme states of matter generated by high-intensity lasers could allow conditions similar to those in the vicinity of black holes to be studied in the lab. The observation of striking similarities between the X-ray spectra emitted by a laser-driven laboratory plasma and those measured from two high-mass binary star systems suggests such potential has been realized.

Laboratory spectroscopy of silicon plasmas photoionized by mimic astrophysical compact objects

Photoionized plasmas are encountered in astrophysics wherever low-temperature gas/plasma is bathed in a strong radiation field. X-ray line emissions in the several kiloelectronvolts spectral range were observed from accreting clouds of binary systems, such as CYGNUS X-3 and VELA X-1, in which high-intensity x-ray continua from compact objects (neutron stars, black holes or white dwarfs) irradiate the cold and rarefied clouds. X-ray continuum- induced line emission accurately describes the accreting clouds, but experimental verification of this photoionized plasma model is scarce. Here we report the generation of photoionized plasmas in the laboratory under well-characterized conditions using a high-power laser. A blackbody radiator at a temperature of 500 eV, corresponding to a compact object, was created by means of a laser-driven implosion. The emerging x-rays irradiate a low-density (n(e) < 10(20) cm(-3)) and low- temperature (T(e) < 30 eV) silicon plasma. Line emissions from lithium- and helium-like silicon ions were observed from a thermally cold silicon plasma in the 1.8-1.9 keV spectral region, far from equilibrium conditions. This result reveals the laboratory generation of a photoionizing plasma. Atomic kinetic calculations imply the importance of direct K-shell photoionization by incoming hard x-rays.

PHOTOIONIZATIONAL PLASMAS. II. COMPUTATIONAL RESULTS

A new computer code, PhiCRE, has been developed to calculate the ionization and population distributions in a photoionizational-collisional-radiative plasma. Comparisons with experiments show that the present code provides rather accurate ionization distributions in photoionized plasmas and show reasonable agreement with other codes. Using this code, we have carried out a systematic study of the behavior of the charge state distributions and the average charge as a function of several parameters of the incident radiation and the plasma parameters.

Time-Dependent Simulation of Photoionized Plasma Created by Laboratory Blackbody Radiator

In recent years, several experiments have been carried out to generate photoionized plasma in a laboratory. In this paper, a computer program is described, which simulates the evolution in time of such laboratory photoionized plasmas. While the experiments provide time-integrated quantities such as average temperature or emission spectrum, the program helps to study the time-dependent development of the underlying processes. A good agreement is obtained between the computational and experimental results.

PHOTOIONIZATIONAL PLASMAS. I. THEORY

In this paper, an attempt is made to define the subject of photoionizational plasmas through rigorous mathematical formalism. The central results of this paper are the following. (1) A set of recursive equations is introduced for the computation of the charge state distributions in photoionizational plasmas. (2) Quantitative validity limits are given for both the collisional and the photoionizational domains. (3) A parameter that determines the charge state distribution in the photoionizational regime is introduced. (4) We provide detailed discussion about the most important components of the emission spectrum in the different equilibrium domains of the emitting plasma. Some of these components have not been reported so far as included in the analysis of such plasmas.

Laser-produced plasmas as unique x-ray souces for industry and astrophysics

Laser produced plasma is one of the brilliant x-ray source that has unique capabilities for use in a wide range of science. Here we describe two examples of laser-produced plasma x-ray source application; one is for the semiconductor device industry and the other is for the astronomy. Extreme ultraviolet (EUV) light sources for microlithography are receiving much attention as an industrial application of laser-produced x-ray source. High power and clean EUV light source, 13.5 nm of wavelength, is developed for mass-production of next generation semiconductor devices. Highest EUV conversion efficiency of 4% has been attained by using low-density and minimum-mass tin targets produced by laser-driven explosion of micro-droplet. In addition, it was recently demonstrated that laser-produced x-ray source is very useful to simulate x-ray astronomical phenomena in the laboratory. A 0.5-keV Planckian x-ray source was created with laser driven implosion for producing non-local-thermodynamical-equilibrium (non-LTE) photoionized plasmas, which is a key to understand astronomical compact objects. Laboratory experiment of non-LTE photoionized plasma offers novel test bed for validation and verification of computational codes used in x-ray astronomy.

Contribution of satellite lines to temperature diagnostics with He-like triplet lines in photoionized plasma

In the present paper, the He α triplet line ratios (resonance, intercombination, and forbidden lines) are computed for photoionized plasmas, when the contributions of nearby satellite lines are taken into account. The computations have been carried out with our radiative-collisional code, RCF, which is based on the flexible atomic code. The calculations of these line ratios have been done for three materials, namely, silicon, magnesium, and neon. Our calculations are used to derive the plasma temperatures for several astronomical objects, where the spectra are emitted from photoionizing plasmas. It is shown that the incorporation of the satellite lines from doubly excited Li-like ions into the He α triplet lines is necessary to obtain reliable temperature diagnostics for these astrophysical objects.

Studies of x-ray emission properties of photoionized plasmas

In this paper three aspects of photoionized plasmas are discussed in both laboratory and astrophysical contexts. First, the importance of accurate atomic/ionic data for the analysis of photoionized plasmas is shown. Second, an overview of present computer codes for the analysis of photoionized plasmas is given. We introduce our computer model, radiative-collisional code based on the flexible atomic code (RCF), for calculations of the properties of such plasmas. RCF uses database generated by the flexible atomic code. Using RCF it is shown that incorporating the satellite lines from doubly excited Li-like ions into the He triplet lines is necessary for reliable analysis of observational spectra from astrophysical objects. Finally, we introduce a proposal to generate photoionized plasmas by x-ray free electron laser, which may facilitate the simulation in lab of astrophysical plasmas in photoionization equilibrium.

Calculation of Photoionized Plasmas with a Detailed-Configuration-Accounting Atomic Model

A computer code has been developed to provide a straightforward, rapid tool for the calculation of the ionization and population distributions in plasmas. To provide rapid response we employ screened hydrogenic model to calculate the energy levels and the rates of radiative processes. The code is designed to interpret photoionization experiments in either steady-state or time-dependent situations. Comparisons with experiments show that the present code provides relatively accurate ionization distributions in photoionized plasmas and show reasonable agreement with other codes.

EMISSION SPECTRUM OF HELIUM-LIKE IONS IN PHOTOIONIZED PLASMAS

The aim of the present paper is to investigate the influence of inner-shell photoionization and photoexcitation on He? and its satellites spectra in photoionized plasmas. An analysis is carried out on the relative importance of the various atomic processes in photoionized plasmas as a function of the electron temperature and irradiation conditions. In particular, we investigate the influence of K-shell photoionization of Li-like ions on the He? spectrum and of Be-like ions on the He? satellites. It is found that in photoionized plasmas these inner-shell processes contribute significantly under low radiation temperature and/or intensity, when Li- and Be-like ions are highly abundant but highly ionized H-like ions are rare. A short discussion is presented about the parameter space in which the excited 1s2p state has statistical or non-statistical distributions, and how such distributions affect the emission spectrum.