V.L. Kantsyrev

Dynamics of Copper Wire Arrays at 1 MA and 20 MA Generators

Experiments to study the implosion dynamics and radiation characteristics of copper z-pinches have been fielded at the 1 MA Zebra facility and the 20 MA Z facility. The impact of initial load mass, initial load diameter, and nesting of wire arrays on the precursor and the stagnated plasma has been evaluated through spectroscopy, shadowgraphy, and fluence measurements. Plasma parameters extracted from modeling of the time-integrated L-shell spectra indicate the presence of more than one plasma source contributing to the radiation, likely due to non-uniform hot spot x-ray emission or temporal gradients.

Analysis of X-ray iron and nickel radiation and jets from planar wire arrays and X-pinches

University-scale Z-pinch devices are able to produce plasmas with a broad range of sizes, temperatures, densities, their gradients, and opacity properties. Radiative properties of such plasmas depend on material, mass, and configuration of the wire array loads. Experiments with two different types of loads, double planar wire arrays (DPWA) and X-pinches, performed on the 1 MA Zebra generator at UNR are analyzed. X-pinches are made from Stainless Steel (69% Fe, 20% Cr, and 9% Ni) wires. Combined DPWAs consist of one plane from SS wires and another plane from Alumel (95% Ni, 2% Al, 2% Si) wires. The main focus of this work is on the analysis of plasma jets at the early phase of plasma formation and the K-and L-shell radiation generation at the implosion and stagnation phases in experiments with the two aforementioned wire loads. The relevant theoretical tools that guide the data analysis include non-LTE collisional-radiative and wire ablation dynamics models. The astrophysical relevance of the plasma jets as well as of spectroscopic and imaging studies are demonstrated.

Radiation from Ag high energy density Z-pinch plasmas and applications to lasing

Silver (Ag) wire arrays were recently introduced as efficient x-ray radiators and have been shown to create L-shell plasmas that have the highest electron temperature (>1.8 keV) observed on the Zebra generator so far and upwards of 30 kJ of energy output. In this paper, results of single planar wire arrays and double planar wire arrays of Ag and mixed Ag and Al that were tested on the UNR Zebra generator are presented and compared. To further understand how L-shell Ag plasma evolves in time, a time-gated x-ray spectrometer was designed and fielded, which has a spectral range of approximately 3.5–5.0 A. With this, L-shell Ag as well as cold Lα and Lβ Ag lines was captured and analyzed along with photoconducting diode (PCD) signals (>0.8 keV). Along with PCD signals, other signals, such as filtered XRD (>0.2 keV) and Si-diodes (SiD) (>9 keV), are analyzed covering a broad range of energies from a few eV to greater than 53 keV. The observation and analysis of cold Lα and Lβ lines show possible correlations w...

Design and Testing of a Load Current Multiplier on Zebra Facility

The Load Current Multiplier concept (LCM) was validated for the first time on a high‐voltage nanosecond pulse‐power generator. The designed new device allowed to increase the load current from the nominal 0.8–0.9 MA up to 1.6 MA in static loads with constant inductance and up to 1.4 MA in a planar wire‐array plasma loads. These results were achieved without modifying the generator energetic or architecture. LCM allowed both the load magnetic energy increase and the increase of soft X‐ray radiation from z‐pinch plasmas.

Scaling of Radiation Parameters of Planar and Compact Cylindrical Wire Arrays at the 1 MA Zebra Generator

Analysis is presented on scaling of radiated x‐ray power, energy and implosion timing of single planar wire arrays (SPWA), double planar wire array (DPWA), and compact cylindrical wire array (CCWA) loads (diameter is 3 and 6 mm) of Mo and W with respect to current peak (0.8–1.4 MA), mass and array dimensions at 100 ns current pulse. Such scaling investigations are important for understanding the potential of these loads as an ICF radiation source7. These data are used to identify promising directions to pursue with regard to highest x‐ray output, smallest load size, and most consistent shot‐to‐shot performance. It is shown that W SPWA and DPWA total energy yield and peak power increased near‐quadratically with current. DPWA scans of inter‐planar gaps from 1.5 mm to 9 mm show an output maximum at 1.5 mm with decreasing output for 6 mm and 9 mm. A DPWA width scan shows that radiation yields decrease slowly as the width is decreased, which may allow for more compact loads without significant sacrifice to the...

X-ray pulse shaping in experiments with planar wire arrays at the 1.6 MA Zebra generator

The shaping of the x-ray radiation pulse is very important in both radiation physics research and Inertial Confinement Fusion studies. The novel planar wire array (PWA) was found to be the effective radiator tested at the university-scale 1.6 MA, 100 ns Zebra generator. The single PWA consists of a single row of wires that are parallel to each other, while the double planar wire array (DPWA) and triple planar wire array (TPWA) include two or three parallel plane wire rows, respectively. All multi-planar geometries resulted in a cascade-type array implosion with a complicated multi-step precursor formation before plasma stagnation. The PWAs (without additional core foam target) feature a dynamic precursor evolution that is a powerful tool for x-ray pulse shaping. The shape and timing of the x-ray pulse from different PWAs were theoretically predicted and experimentally analyzed for a variety of planar wire arrays.

Modeling of K‐Shell Al and Mg and L‐Shell Mo Radiation from Compact Cylindrical Wire Array Plasmas Produced on the 1 MA UNR Zebra Generator

K‐shell radiation of Al and Mg and L‐shell radiation of Mo from implosions of compact cylindrical wire arrays (CCWA) on the 1 MA UNR Zebra generator was studied. Specifically, radiation from implosions of 3 and 6 mm CCWA with (16–24) Al‐5052 (95% Al and 5% Mg) and Al‐5052 (97.5% Al and 2.5% Mg) and Mo wires was analyzed using the full set of diagnostics: PCD and current signals, and X‐ray pinhole images and spectra. Previously developed non‐LTE models were applied to model spatially resolved time integrated as well as time‐gated spatially integrated spectra from Al, Mg, and Mo plasmas. Derived electron temperature and density spatial gradients as well as percentage of radiating mass were studied and compared. In addition, the novel Wire Dynamics Model (WDM) was used to analyze the implosion dynamics of compact wire array loads.

Studying Radiation from Z‐pinch Wire Array and X‐Pinch Plasmas: K‐shell Mg to M‐shell Mo

University‐scale Z‐pinch generators are able to produce plasmas with a broad range of temperatures, densities, and opacity properties depending on the type, size, and mass of wire‐array loads and wire materials. Experiments with very different Z‐pinch loads were performed on the 1 MA Zebra generator at UNR and analyzed during the last five years including Single and Nested Cylindrical, Conical, and various types of Planar Wire Arrays. It is shown that such wire arrays are good sources of x‐rays and that they produce significant radiation yield (up to 25 kJ) on a ns time scale, and generate bright spots of sub‐mm size. They can be used for studying radiative properties of moderate density (between 1018 cm−3 and 5×1021 cm−3) and temperature (⩽1.5 keV) plasmas. In addition, X‐pinches generated higher density (>1022 cm−3) and temperature (>2 keV) plasmas on scales as small as a few μm to several mm in size. Wire materials with a broad range of nuclear charge Z were used, ranging from low‐Z, such as alloyed Al...

Implosion Dynamics in Conical Wire Array Z-pinches

We present initial results from imploding conical wire array experiments performed on both the MAGPIE generator (1MA, 240ns) at Imperial College London and the Nevada Terawatt Facility’s Zebra generator (1MA, 100ns) at University of Nevada, Reno. This paper will discuss the implosion dynamics of conical wire arrays, including initial implosion of the cathode end of the array and the formation of a magnetic bubble.

Self-proton/ion radiography of laser-produced proton/ion beam from thin foil targets

Protons and multicharged ions generated from high-intensity laser interactions with thin foil targets have been studied with a 100 TW laser system. Protons/ions with energies up to 10 MeV are accelerated either from the front or the rear surface of the target material. We have observed for the first time that the protons/ions accelerated from the front surface of the target, in a direction opposite to the laser propagation direction, are turned around and pulled back to the rear surface, in the laser propagation direction. This proton/ion beam is able to create a self-radiograph of the target and glass stalk holding the target itself recorded through the radiochromic film stack. This unique result indicates strong long-living (ns time scale) magnetic fields present in the laser-produced plasma, which are extremely important in energy transport during the intense laser irradiation. The magnetic field from laser main pulse expands rapidly in the preformed plasma to rotate the laser produced protons. Radiati...