Alla S. Shlyaptseva

Energetic electron beam generation and anisotropy of hard x-ray emission from 0.9 to 1.0 MA high-Z X pinches

An analysis of the energy, spatial character, and temporal evolution of electron beams and hard x rays from 0.9 to 1.0 MA high-Z X pinches is presented. Experimental results from Ti, Fe, Mo, and W X pinches show that X pinches are an effective source of hard x rays with energies greater than 30 keV. Electron beams with energies up to 2 MeV higher than the applied anode-cathode voltage are generated along the pinch axis before the maximum current is reached. The beams have diameters of about 3 mm and generate bursts of hard x rays with sizes between 1 and 2 mm and total time durations of up to 150 ns. The measured 100–500 keV x-ray distribution is spectrally anisotropic. Hard x-ray synchrotron radiation in the side-on direction is proposed as a possible explanation of this anisotropy.

X-ray spectropolarimetry of high-temperature plasmas

X-ray spectropolarimetry is a powerful new tool for investigating the anisotropy of high-temperature plasmas. It is sensitive to the energetic electron distribution function and magnetic field, which, in general, have not been measured adequately. This diagnostic is based on the theoretical modeling of x-ray line polarization-dependent spectra measured simultaneously by spectrometers with different sensitivities to polarization. The increasing sophistication of spectroscopic monitoring of high-temperature plasmas has led to the necessity to account for both non-Maxwellian electron distribution functions and polarization properties of lines. This diagnostic can be applied to a broad range of plasmas, from low-density astrophysical plasmas to dense z-pinch plasmas. This work shows how x-ray spectropolarimetry complements the usual spectroscopic monitoring of hot plasmas and demonstrates the importance of accounting for x-ray line polarization in plasma diagnostics.

The dense Z-pinch program at the University of Nevada, Reno

A new program of research into the physics of dense z-pinches is being initiated around a high-repetition-rate two-terawatt generator (formerly Zebra/HDZP-II: 2MV, 1.2 MA, 100 ns, 200 kJ, 1.9 Ω final line impedance) transferred to the University of Nevada. Reno Physics Department from Los Alamos National Laboratory. Areas for study include the early-time evolution of a current-driven wire, the plasma turbulence around and between wires, the suppression or reduction of instabilities, the nature of x-ray bright spots, and the tailoring of the x-ray emission spectrum. Novel loads that introduce a stabilizing velocity shear or density profile will be examined, along with configurations that promise to increase the quantity, hardness, stability, and reproducibility of x-ray emission. A wide variety of diagnostics are being developed, so as to diagnose the plasma thoroughly and make detailed comparisons between experiment, computer simulation, and theory. These include x-ray, soft x-ray, and extreme ultraviolet...

Advanced x-ray and extreme ultraviolet diagnostics and first applications to x-pinch plasma experiments at the Nevada Terawatt Facility

A wide variety of x-ray and extreme ultraviolet (EUV) diagnostics are being developed to study z-pinch plasmas at the Nevada Terawatt Facility at the University of Nevada, Reno. Time-resolved x-ray/EUV imaging and spectroscopy, x-ray polarization spectroscopy, and backlighting will be employed to measure profiles of plasma temperature, density, flow, and charge state, and to investigate electron distribution functions and magnetic fields. The instruments are state-of-the-art applications of glass capillary converters (GCC), multilayer mirrors (MLM), and crystals. New devices include: a novel GCC-based two-dimensional imaging spectrometer, a six-channel crystal/MLM spectrometer (“polychromator”) with a transmission grating spectrometer, and two sets of x-ray/EUV polarimeters/spectrometers. An x-pinch backlighter is under development. X-ray polarimeter/spectrometer, a survey spectrometer, a multichannel time-gated x-ray pinhole camera, and filtered fast x-ray diodes have observed the structure of Ti and Fe ...

Polarization of x-ray Li- and Be-like Fe satellite lines excited by an electron beam

We have calculated the polarization properties of dielectronic satellite lines in Li- and Be-like Fe ions excited through resonance electron capture by a monoenergetic electron beam. Following the density matrix formalism, we have computed the degree of polarization and the spectral intensity distribution of dielectronic satellites associated with a given polarization state. Theoretical results were compared with experiments performed at the Livermore Electron Beam Ion Trap where satellite line emission from Fe ions was simultaneously recorded with two crystal spectrometers. These results are relevant to diagnostic applications of x-ray line polarization spectroscopy in plasmas.

Precise measurements and theoretical calculations of He-like ion resonance line satellites radiated from Be-, B-, C-, N-, O-, and F-like ions

Spectra with spectral resolution λ/Δλ 3000-7000 in the vicinity of the He-like ion resonance lines Mg, Al, Si, P, S were obtained in CO2 laser-produced plasma. The wavelengths of these satellites were measured and compared with numerical calculations. Identification of lines or a group of overlapping lines was performed. Twenty-two transitions of dielectronic satellites for Be-like ions, 41 transitions for B-like, 40 transitions for C-like, 22 transitions for N-like, 12 transitions for O-like ions and 2 transitions for F-like ions were identified. The average between theoretical and experimental wavelengths was ±(0.0005-0.001)A, but in some cases it was ±(0.002-0.003)A.

X-ray spectroscopy and spectropolarimetry of high energy density plasma complemented by LLNL electron beam ion trap experiments

X-ray spectra of high energy density (HED) Z-pinch plasmas have been analyzed by means of a comprehensive kinetic modeling. A new diagnostic, x-ray spectropolarimetry, was applied to study anisotropy of Z-pinch plasma. This diagnostic is based on theoretical modeling of polarization-dependent spectra measured simultaneously by spectrometers with different sensitivity to polarization. Specifically, K-shell emission from Ti X-pinches was recorded simultaneously with identical LiF crystal spectrometers with the dispersion plane perpendicular and parallel to the discharge axis. Spectroscopic results from seven Ti X-pinch shots have been analyzed. Similar K-shell Ti polarization-dependent spectra generated by a quasi-Maxwellian electron beam at the LLNL EBIT-II electron beam ion trap have been studied. Further, the EBIT-II M-shell W spectra have proved to be important in the development of M-shell diagnostics of HED Z-pinch plasma. The advantages provided by electron beam ion trap data in the interpretation of...

Studies of energetic electrons with space and time resolution in Mo and W X-pinches from measurements of x rays >9 keV

Electron beams in 400 kA peak current Mo and W X-pinches have been studied using 1 ns time-resolution Si diodes to monitor x rays >9 keV. Softer x rays were monitored by photoconducting detectors (PCDs). Three different types of higher energy x-ray bursts were observed. The first type appears to be produced by electrons generated starting at the moment of, or immediately after, the first thermal x-ray burst (typically 40–50 ns after the current start), and Si detector signals last 1–2 ns. The second type of harder x-ray burst occurs 50–80 ns after the current start, lasts 2.5–10 ns, and is typically not correlated with a thermal x-ray burst. These two types of bursts were generated near the cross-wire region. The third type of x-ray burst occurs 70–100 ns after the current start, and is also uncorrelated with PCD signals. The energetic electrons responsible for these x rays are generated for 10–30 ns, and the radiation is produced in the anode region.

Development of M-shell x-ray spectroscopy and spectropolarimetry of z-pinch tungsten plasmas

The development of spectroscopic modeling of M-shell tungsten z-pinch plasma is presented. The spectral region from 3.5 to 6.5 A includes three distinct groups of transitions, and the best candidates for M-shell diagnostics are identified. Theoretical modeling is benchmarked with LLNL electron beam ion trap data produced at different energies of the electron beam and recorded by crystal spectrometers and a broadband microcalorimeter. A new high temperature plasma diagnostic tool, x-ray spectropolarimetry, is proposed to study polarization of W line emission and is illustrated using the results of x-pinch polarization-sensitive experiments. The x-ray line polarization of the prominent M-shell tungsten lines is calculated, and polarization markers are identified. The advantage of using x-pinch W wire experiments for the development of M-shell diagnostics is shown.

X-ray spectroscopy for high energy-density X pinch density and temperature measurements (invited)

X pinch plasmas produced from fine metal wires can reach near solid densities and temperatures of 1 keV or even more. Plasma conditions change on time scales as short as 5–10 ps as determined using an x-ray streak camera viewing a focusing crystal spectrograph or directly viewing the plasma through multiple filters on a single test. As a result, it is possible to determine plasma conditions from spectra with ∼10 ps time resolution. Experiments and theory are now coming together to give a consistent picture of the dynamics and kinetics of these high energy density plasmas with very high temporal and spatial precision. A set of diagnostic techniques used in experiments for spectrally, temporally, and spatially resolved measurements of X pinch plasmas is described. Results of plasma parameter determination from these measurements are presented. X ray backlighting of one x- pinch by another with ∼30 ps x-ray pulses enables the dynamics and kinetics to be correlated in time.