E. Stambulchik

Stark effect of high-n hydrogen-like transitions: quasi-contiguous approximation

Calculations of line shapes of highly excited (Rydberg) atoms and ions are important for many topics in plasma physics and astrophysics. However, the Stark broadening of the radiative transitions originating from high-n levels of hydrogen or hydrogen-like ions is rather complex, making the detailed calculations of their spectral structure very cumbersome. Here, we suggest a simple analytical method for an approximate calculation of such line shapes. The utility of the method is demonstrated in application to the line broadening in plasma, where a very good accuracy is achieved over a range of transitions, species and plasma parameters.

Plasma dynamics in pulsed strong magnetic fields

Recent investigations of the interaction of fast-rising magnetic fields with multi-species plasmas at densities of 1013–1015 cm−3 are described. The configurations studied are planar or coaxial interelectrode gaps pre-filled with plasmas, known as plasma opening switches. The diagnostics are based on time-dependent, spatially resolved spectroscopic observations. Three-dimensional spatial resolution is obtained by plasma-doping techniques. The measurements include the propagating magnetic field structure, ion velocity distributions, electric field strengths, and non-Maxwellian electron energy distribution across the magnetic field front. It is found that the magnetic field propagation velocity is faster than expected from diffusion. The magnetic field evolution cannot be explained by the available theoretical treatments based on the Hall field (that could, in principle, explain the fast field propagation). Moreover, detailed observations reveal that magnetic field penetration and plasma reflection occur si...

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.

Self-pulsing 104 A cm−2 current density discharges in dielectric barrier Al/Al2O3 microplasma devices

Excitation of Al/Al2O3 microplasma devices with 50 μs, 800 V pulses produces, in Ar/H2 gas mixtures at 600 Torr, ∼6 A current pulses with a duration of ∼30 ns. Corresponding to peak current and power densities of ∼104 A/cm2 and ∼2.5 GW/cm3, respectively, these pulses are generated in a 10 μs burst in which the voltage self-pulses at a repetition frequency of ∼3 MHz. Analysis of the Hα, Hβ, and Ar II emission line profiles yields a plasma density of ∼1017 cm−3, and the emission of O IV ions suggests the presence of energetic electrons. Images of the microplasma indicate that the plasma is initiated by surface flashover and extends ∼200 μm outside the microcavity.

Beyond Zeeman spectroscopy: Magnetic-field diagnostics with Stark-dominated line shapes

A recently suggested spectroscopic approach for magnetic-field determination in plasma is employed to measure magnetic fields in an expanding laser-produced plasma plume in an externally applied magnetic field. The approach enables the field determination in a diagnostically difficult regime for which the Zeeman-split patterns are not resolvable, as is often encountered under the conditions characteristic of high-energy-density plasmas. Here, such conditions occur in the high-density plasma near the laser target, due to the dominance of Stark broadening. A pulsed-power system is used to generate magnetic fields with a peak magnitude of 25 T at the inner-electrode surface in a coaxial configuration. An aluminum target attached to the inner electrode surface is then irradiated by a laser beam to produce the expanding plasma that interacts with the applied azimuthal magnetic field. A line-shape analysis of the Al III 4s–4p doublet (5696 and 5722 A) enables the simultaneous determination of the magnetic field...

Atomic emission spectroscopy in high electric fields

Pulsed‐power driven ion diodes generating quasi‐static, ∼10 MV/cm, 1‐cm scale‐length electric fields are used to accelerate lithium ion beams for inertial confinement fusion applications. Atomic emission spectroscopy measurements contribute to understanding the acceleration gap physics, in particular by combining time‐ and space‐resolved measurements of the electric field with the Poisson equation to determine the charged particle distributions. This unique high‐field configuration also offers the possibility to advance basic atomic physics, for example by testing calculations of the Stark‐shifted emission pattern, by measuring field ionization rates for tightly‐bound low‐principal‐quantum‐number levels, and by measuring transition‐probability quenching.

Plasma formulary interactive

We present an interactive, Web-based application that provides a comfortable access to evaluating, comparing, and plotting of a multitude of different plasma and atomic physics parameters, grouped by the unit dimensions. A special attention is devoted to the Stark broadening which is calculated with a good accuracy for transitions between degenerate atomic levels. The list of the entities calculated encompasses over one hundred entries and is easily expandable. The application is built using open-source components and is compatible with a majority of modern browsers.

K-line emission profiles with focus on the self-consistent calculation of plasma polarization

The emitted K α -spectra of moderately ionized titanium radiators in a medium are used to determine plasma temperature and composition in electron heated target regions. A theoretical treatment of spectral line profiles using self-consistent Hartree-Fock and ion sphere model calculations to determine the influence of plasma polarization is applied. We confirm the importance of excited emitter states for line shape modeling.

Absorption-aided x-ray emission tomography of planar targets

Suggested is a tomography-like method for studying properties of solid-density plasmas with cylindrical symmetry, such as formed in the interaction of high-power lasers with planar targets. The method is based on simultaneous observation of the target x-ray fluorescence at different angles. It can be applied for validation of existing hypotheses and lately for reconstruction of the plasma properties with three-dimensional resolution. The latter becomes straightforward if the resonance x-ray self-absorption is negligible. The utility of the method is demonstrated by examples.

Investigation of plasma formation and propagation in relativistic electron beam diodes

Summary form only given: A series of experiments were conducted at Sandia National Laboratories on the RITS-6 accelerator configured in the low impedance mode (7.5 MV, 180 kA) to investigate electrode plasma formation and propagation in relativistic electron beam diodes used for flash x-ray radiography. In particular the Self- Magnetic Pinch diode (SMP), which employed a hollow metal cathode positioned ~12 mm from a thin aluminum foil anode, in-front of a high atomic number bremsstrahlung x-ray converter, was studied. Anode and cathode plasmas composed of surface contaminants and metals with densities of up to 1017 cm-3 are formed and expand across the gap with velocities of 10s of cm/microsecond. It is believed that the dynamics and interactions of these plasmas are responsible for the observed impedance behavior of the diode. Visible and ultraviolet spectroscopy is used to spatially and temporally measure individual plasma species. Plasma densities and temperatures are determined using collisional-radiative models. Diagnostics include gated, intensified CCD camera imaging and gated/streaked spectroscopy using high resolution 1 meter Czerny-Turner monochromators. Recent results are presented.