X-pinch Wire Research Articles

K-shell radiation and bright spot characteristics of high-energy-density Fe-Cr-Ni plasmas influenced by X-pinch load geometry

K-shell radiation is diagnostically advantageous for the study of high-energy-density plasmas. The current work investigates the influence of load geometry on K-shell x-rays in Z-pinch plasmas produced on the 1-MA Zebra generator. Stainless steel (Fe: 69%, Cr: 20%, Ni: 9%) X-pinch wire loads are fielded with an interwire angle of 31° (small-angle) or 62.5° (large-angle), respectively and studied using various x-ray diode, imaging, and spectroscopic diagnostics. The large-angle geometry produced large, individual x-ray-emitting bright spots (> 3 keV) at the wire cross-point averaging areas ≥ 1 mm2, with noteworthy soft x-ray (> 0.75 keV) bursts and radiation yields ≤ 14.6 kJ. The small-angle geometry produced multiple x-ray-emitting bright spots extending the pinch axis with smaller average sizes (≤ 0.5 mm2), consistent with stronger current, increased radiation yield (≥ 15.5 kJ), and notable hard x-ray (> 9 keV) bursts, which peak with largest cumulative bright spot size. Spectroscopic analysis is performed with non-LTE collisional-radiative modeling, indicating a cold, nonthermal plasma region radiating from neutral to Ne-like ions, a hot, thermal region radiating from Fe and Cr He- and Li-like ions, and an intermediate region radiating Kα satellites from Li-like to O-like ions. Modeling of the nonthermal and satellite features imply a fractional hot electron abundance ∼0.1% and ∼0.5% for large- and small-angle geometries, respectively. Relative intensity analysis is performed on Heα and Kα lines, revealing intensity ratios that deviate from the original wire composition. Optical depth estimates allude to optically thick, thermal K-shell plasmas with densities consistent with non-LTE modeling.

Numerical Simulation on the Formation and Pinching Plasma in X-pinch Wires on 2-D Geometry

This paper deals with the computational work to characterize the formation and pinching of a plasma in an X-pinch configuration. A resistive magnetohydrodynamic model of a single fluid and two temperature is adopted assuming a hollow conical structure in the (r,z) domain. The model includes the thermodynamic parameter of tungsten from the corrected Thomas-Fermi EOS(equation of state), determining the average ionization charge, pressure, and internal energy. The transport coefficients, resistivity and thermal conductivity, are obtained by the corrected Lee & More model and a simple radiation loss rate by recombination process is considered in the simulation. The simulation demonstrated the formation of a core-corona plasma and intense compression process near the central region which agrees with the experimental observation in the X-pinch device at Seoul National University. In addition, it confirmed the increase in radiation loss rate with the density and temperature of the core plasma. Keywords: X-pinch, Magnetohydrodynamics, Exploding Wires Keywords: 엑스핀치, ìžê¸°ìœ ì²´ì—­í•™, ì„¸ì„ í­ë°œ

Underwater Electrical Explosion of Wires and Wire Arrays and Generation of Converging Shock Waves

A brief review of the results obtained in recent research of underwater electrical explosions of wires and wire arrays using microsecond-, submicrosecond-, and nanosecond-timescale high-current generators is presented. In a microsecond-timescale wire explosion, good agreement was attained between the results of experiments and the results of magnetohydrodynamic calculations coupled with equations of state (EOS) and modern conductivity models. Conversely, in a nanosecond-timescale wire explosion, the wire resistance and the EOS were modified in order to fit experimental data. In experiments with cylindrical and spherical wire arrays, generation of a converging shock wave (SW) was demonstrated allowing formation of an extreme state of water in the vicinity of either the axis or the origin of the SW’s implosion. In addition, it is shown that SW convergence in superspherical geometry allows one to achieve larger values of pressure, density, and temperature of water in the vicinity of the axis of convergence than in the case of a spherical implosion. The results of experiments and numerical analysis showed that a cylindrical SW keeps its symmetry along the main path of its convergence. In addition, it is shown that underwater electrical explosion of an X-pinch wire configuration and a cone wire array allows one to generate fast jets of metal and water, respectively, without using chemical explosions.

Timing of x-ray burst from X-pinch

The x-ray burst timings of X-pinches, TXB, made using eight different wires for different current were measured. The results showed that a higher current makes a shorter TXB for a given X-pinch wire. In other words, TXB scales linearly with the line mass density for a given current. Based on the snow-plow model for Z-pinch plasma, it was derived that for a given X-pinch wire the integral of the current over time from zero to TXB is constant, i.e., ∫0TXBi(t)⋅dt=const.. This theoretically derived relation was confirmed by our experiments.

Experimental study of the neck formation in an X pinch

X-pinch experiments have been performed on a compact 250 kA, 180 ns pulsed power generator specially designed for this purpose at the Institute of High Current Electronics (Tomsk, Russia). The X pinches were composed of two molybdenum wires of diameter 25 μm making an angle of 36° with the z-axis. The X-pinch dynamics was recorded with a 3 ns exposure time using an HSFC Pro four-frame camera. Axial plasma jets propagating toward both the anode and the cathode were observed. The jets became noticeable within 10 ns after the onset of current flow, which approximately corresponded to the time at which the electrical explosion of the X-pinch wires occurred. The velocity of the anode-directed jet reached 107 cm/s, which was about 1.5 times the velocity of the cathode-directed jet. These high jet velocities are inconsistent with the plasma temperature resulting from the wire explosion. Hence, these jets seem to develop due to implosion of the light plasma layer stripped by magnetic forces from the wire surface, and the increase in their velocities is perhaps due to cumulative effects taking place at the X-pinch axis. The X-pinch neck formed as a rule above the initial wire cross point (closer to the anode). In this region, the plasma diameter gradually increased with time and then drastically decreased 10-15 ns prior to the x-ray pulse. Immediately before the x-ray pulse, in the (250-300 μm long) plasma neck, a lower scale constriction developed, forming a "hot spot". It has been confirmed that the anode-directed plasma jet could take some part of the X-pinch wire current because of the evident jet pinching in the anode region. This process seems to determine the neck length.

Theoretical and experimental studies of the radiative properties of matter at high energy densities and their application to the problems of inertial confinement fusion

The paper presents the results of theoretical and experimental studies of the radiative properties of plasmas produced by heating and compression of various materials to high energy densities. The specific features of the theoretical plasma model known as the ion model, which is used to calculate the radiative characteristics of plasmas of complex chemical composition, are discussed. The theoretical approach based on this model is applied to the plasma produced during the explosion of the X-pinch wires. The theoretical estimate of the radiation efficiency is compared with the experimental data on the total energy yield from an X-pinch made of two different wires (NiCr and Alloy 188). The radiative characteristics of (C12 H16 O8) and (C8 H12 O6) plasmas are calculated for the temperature diagnostics of plasmas produced from porous targets employed in inertial confinement fusion experiments with the use of laser radiation and heavy-ion beams.

Aluminum and tungsten X-pinch experiments on 100 kA, 100 ns linear transformer driver stage

X-pinch experiments have been carried out on a 100 kA, 100 ns linear transformer driver stage recently built up. The X-pinches exhibited a source size of about 10 μm, a pulse duration of 3 ns, 3–5 keV radiation energy of 3.9 mJ, and a burst time jitter of tens of nanosecond with the 2-wire 8 μm W X-pinch load. The generator output current and the X-pinch characteristics depended on the X-pinch wire materials in the tests. X-ray backlighting images from the insects showed the significant phase-contrast effect.

Multiwire$X$-Pinches at 1-MA Current on the COBRA Pulsed-Power Generator

The rebuilt COBRA pulsed-power generator, which has a variable current-pulse waveform and amplitude (95-150-ns rise time and ~1-MA peak current), has extended the range of the current-pulse parameters that can be used to study the X-pinches. X-pinches with 4-12 wires of several different wire materials (from Al to W) with diameters from 25 to 75 mum have been studied. The influence of the rate of the rise of current and the X-pinch wire mass on the X-pinch plasma formation and pinch implosion dynamics has been studied using a set of diagnostics with spatial and/or temporal resolution. Multiwire X-pinches were placed in the diode center, and/or two four-wire X-pinches were placed in one of the four parallel return-current circuits of the diode. The experiments showed that the most important factor determining the first X-ray burst timing is the linear mass density of the X-pinch wires, and an optimal value for obtaining a single high-energy X-ray burst was found. Radiographic images of the different test objects, wires in wire-array Z-pinches, and the X-pinches, themselves, were obtained using a micrometer-scale spatial resolution

$X$-Pinches in Dielectric Frames

The experiments reported here were designed to test X-pinch wire-loading configurations using a simple plastic frame that might enable the X-pinch wires to be changed under vacuum after a pulse. Several frame configurations and materials were tested, some of which suffered from early surface flashover and current shunting away from the X-pinch. Fiberglass frames proved to be successful both in minimizing the current shunting up to the time of the X-pinch X-ray burst and, in most tests, in substantially reducing X-ray emission from energetic electrons and secondary soft X-ray bursts following the first X-ray burst. Both of these features are beneficial for using X-pinches for point-projection radiography as well as for recording X-ray spectra from the X-pinches or other nearby plasmas