L. Weingarten

Progress in line-shape modeling of K-shell transitions in warm dense titanium plasmas

Modeling of x-ray spectra emitted from a solid-density strongly coupled plasma formed in short-duration, high-power laser–matter interactions represents a highly challenging task due to extreme conditions found in these experiments. In this paper we present recent progress in the modeling and analysis of Kα emission from solid-density laser-produced titanium plasmas. The self-consistent modeling is based on collisional-radiative calculations that comprise many different processes and effects, such as satellite formation and blending, plasma polarization, Stark broadening, solid-density quantum effects and self-absorption. A rather strong dependence of the Kα shape on the bulk electron temperature is observed. Preliminary analysis of recently obtained experimental data shows a great utility of the calculations, allowing for inferring a temperature distribution of the bulk electrons from a single-shot measurement.

Effect of radiative cascades on intensities of dielectronic satellites to Heα

Radiative cascades into autoionizing states 1s2l2l 0 in Li-like ions are studied. The correction function that describes the effect of cascades on level populations is calculated using the 1/Z-expansion method for the range of nuclear charges Z = 10‐30. It is shown that for the q-satellite, which is often used in hot plasmas for diagnostic purposes, the contribution of radiative cascades may be three orders of magnitude larger than the direct dielectronic capture. Time-dependent collisional‐radiative modeling is used to calculate satellite intensities and determine spectra modifications due to radiative cascades.

Investigation of the hydromotion and ion and electron temperatures of stagnating Z-pinch plasma using time- and space-resolved K-line spectra

Summary form only given. Even though the physics of Z-pinch systems is understood in general, there is a severe lack of detailed experimental data on the thermalization processes and dynamics that govern the pinch behaviour, and on the plasma parameters during the stagnation phase. Here, we report on a novel spectroscopic system, used to determine temporally-resolved ion kinetic energy and temperature, electron temperature and density, and spatial correlation between different charge-states species of the stagnating plasma. We use a neon Z-pinch, imploding under a 500-kA, 500-ns current pulse, and observe a hot-and-dense plasma core stagnating on axis for ~10 ns, emitting ~1 kJ of radiation. A two-spectrometer diagnostic system is employed, simultaneously recording two groups of optically-thin lines: He-like satellites to Lyα and high-n H-like Lyδ and Lyε lines, with ultra-high spectral, temporal and spatial resolutions. All data are axially imaged across the stagnation column. The ion temperature is obtained simultaneously from the Stark broadening of hydrogenic-line emission and from the Doppler broadening measurements coupled with energy-balance considerations, and is found to be substantially lower than the hydrodynamic-motion energy. Furthermore, the two-spectrometer system provides a unique insight into the temporal and spatial correlations between the intensities of the spectral lines emitted by different ionic charge-states in the stagnating plasma. Together with kinetics modeling and argumentation, these measurements allow for inferring space-and time-resolved electron density and temperature. This also includes determining the gradients of the electron temperature, and the mechanism of populating the doubly-excited states, along the pinch column.

Visible spectroscopy characterization of aluminum X pinch plasmas

Summary form only given. We are initiating an experiment in which time resolved visible spectroscopy will be used to characterize the plasma in and near the minidiode in aluminum (Al) X pinches. The goal of the experiment is to determine the magnetic field and other plasma conditions near the outer radius of the imploding z-pinch in the minidiode. At this location the conditions should be suitable for a magnetic field measurement using the Al doublet previously used for Zeeman Broadening measurements at the Weizmann Institute of Science.1 We will be studying 2-wire and hybrid X pinches on the 13kA 430ns rise time Low Current Pulser 3 (LCP3), the 20kA 200ns rise time Low Current Pulser 4 (LCP4), and at ≥ 200kA on the 50ns rise time XP generator. By using various pulsers and current levels we aim to study directly the impact that the driving current has on the development of the minidiode of the X pinch, the magnetic field, the electron temperature, and the electron density as a function of time and space. Preliminary results will be presented.

Investigation of the dynamics of stagnating high-energy-density plasma using a novel technique for the determination of the ion temperature

Summary form only given. The thermalization and energy conversion to radiation in high-energy-density plasma is a topic of broad interest in laboratory plasmas and in astrophysics. Knowledge of the ion temperature is of decisive importance, since this parameter determines the rate of various processes, including that of the energy transfer to electrons. We here report on the development of a novel spectroscopic method for determining the ion temperature in the stagnating plasma, based on the Stark broadening of hydrogenic-line emission from moderately-coupled ions in the stagnating plasma. We use a neon Z-pinch, imploding under a 500-kA, 500-ns current pulse. Two spectroscopic systems with ultra-high-resolutions in spectrum, space, and time are employed simultaneously. A major emphasis has been put on measurements of the spectra of two different optically-thin lines: satellites to Lyα and Lyδ. While the optical thinness is invaluable in diagnosing the ion velocity distribution, the electron density, and the ion temperature, the low-intensity of such lines required the use of toroidal crystals, for enhancing the light-collection efficiency. All data were axially imaged across the stagnation column. We demonstrate the first employment of the spectroscopic method, which yields an ion temperature that is compared to previous measurements that were based on Doppler broadening and energy-balance considerations1,2. In addition, the data allowed for observing temporal and spatial correlations between the shapes of the various lines that are used to infer details of the distributions of the electron density and temperature in the stagnating column.

Time resolved visible spectroscopy characterizations of single wire aluminum plasmas

The conditions within plasmas generated by current-driven explosions of single 15–50µm aluminum (Al) wires are being investigated using time-resolved emission spectroscopy at visible wavelengths. The experiments are being carried out at Cornell University on the 10kA, 500ns rise time Low Current Pulser 3 (LCP3). The plasma parameters being determined as a function of time and radial position include electron temperature and density, ionization state and magnetic field. To determine the magnetic field, a new diagnostic method is being developed which makes use of Zeeman-effect-produced differences in the line shapes of two fine structure components of a multiplet that are equally broadened by both Stark effect and Doppler broadening. This method has been demonstrated at the Weizmann Institute of Science (WSI) in laser-produced plasmas [1] with lower energy densities than are being studied here. As in the work at WSI, we use the Al III [4s–4p] transitions at 5696Å and 5722Å to determine the magnitude of the magnetic field. In the experimental plasmas generated by LCP3, electron number densities are in the range 1017–1018cm−3 while electron temperatures are between 2 and 5eV. Under these conditions, seen close to peak current 300 µm away from the wire, the line broadening due to a magnetic field of 6.5 T is calculated to be 3.0 Å while the Stark broadening at 1018/cm3 is calculated to be 3.5 Å; the Doppler broadening is negligible. The total FWHM difference of the doublet lines resulting from these mechanisms is estimated to be 10%. We are setting up a new spectroscopic system capable of clearly detecting this difference after carrying out preliminary experiments on a lower resolution system. Initial high-resolution data will be presented.

Mean specific intensity of radiation in cylindrical and spherical plasmas

We present an easy-to-use formula for mean (space- and direction-average) specific intensity of radiation in uniform spherical and cylindrical plasmas, which are not under external irradiation. This formula has high accuracy in any spectral interval dn taken in continuum as well as within a spectral line of any profile, including overlapping lines and lines on a pedestal of intense continuum in any spectral range. The formula considerably accelerates self-consistent computations of the radiation field and the distribution of ions over their ionization degrees and quantum states. It may also be used for computations of any radiation dependent-quantity, for example, the photoionization probability.