High Current Z-pinch Research Articles

On the Possibility of Observing Stimulated De-Excitation of Nuclear Isomer 186mRe in a High-Current Z-Pinch Plasma at the ANGARA-5-1 Setup

On the Possibility of Observing Stimulated De-Excitation of Nuclear Isomer 186mRe in a High-Current Z-Pinch Plasma at the ANGARA-5-1 Setup

Increasing the Specific Energy Concentration of High-Current Z-Pinch Plasma by Using Transient Compression Modes

Increasing the Specific Energy Concentration of High-Current Z-Pinch Plasma by Using Transient Compression Modes

Generation of a Beam of Fast Electrons, Plasma Bremsstrahlung, and Characteristic Radiation in a High-Current Z-Pinch

The generation of accelerated electron beams in a high-current Z-pinch formed by the implosion of wire cylindrical tungsten arrays on an Angara-5-1 facility is studied. The most intense characteristic and bremsstrahlung X-ray radiation of fast electrons is recorded from the central region of the pinch at the pin-ching stage. The transverse size of the radiation source in the characteristic tungsten radiation Lα is ~1.5‒1.8 mm, which is close to the transverse size of the radiation source in the soft X-ray emission (1‒1.5 mm). The current of accelerated electrons generated during the implosion of the wire array and the formation of a pinch is on the order of the Alfven current (IA). This result is consistent with the estimate of the current of accelerated electrons made from the measured characteristic radiation intensity Lα of tungsten under the assumption that the mean free path of fast electrons in a pinch is on the order of its length.

The inverse skin effect in the Z-pinch and plasma focus

The inverse skin effect and its influence on the dynamics of high-current Z-pinch and plasma focus discharges in deuterium are analyzed. It is shown that the second compression responsible for the major fraction of the neutron yield can be interpreted as a result of the inverse skin effect resulting in the axial concentration of the longitudinal current density and the appearance of a reversed current in the outer layers of plasma pinches. Possible conditions leading to the enhancement of the inverse skin effect and accessible for experimental verification by modern diagnostics are formulated.

A fast time-response bolometer for soft X-ray radiation energy measurements in a high-current Z-pinch

A high-sensitivity bolometer with a short time response to heating with external radiation has been developed. It is intended for measuring the integral parameters of soft X-ray radiation of liner plasma. The bolometer is adapted to the conditions of explosion experiments with an increased level of electromagnetic pickups at facilities that are based on magnetic-explosion generators with megaampere currents. The bolometer has a metal casing for improving the noise immunity of measurements. A 2-μm-thick nickel foil is used as the material for the resistive element of the working substance of the bolometer. The choice of the material and the geometrical dimensions of the bolometer working elements were analyzed. The ultimate thermal load on the bolometer was determined. A technique for calibrating the working elements using a pulse current was developed. The working capacity, good noise immunity, and a high sensitivity of the bolometer were demonstrated in experiments. The dynamic range in measurements of the surface energy density of X rays is 0.03–0.3 J/cm2.

Experimental study of the ion flux parameters and anode plasma dynamics in the Angara-5-1 facility

Results are presented from experimental studies of the anode plasma dynamics and measurements of the ion flux ejected along the axis of a high-current Z-pinch. Pinch discharges were formed by the implosion of tungsten wire arrays in the Angara-5-1 facility. It is shown that the ion energy spectrum depends on the mass and configuration of wire arrays, as well as on the diameter of the anode aperture. The shape of the ion spectrum indicates that the plasma propagates in the form of a compact plasmoid. Shadow and X-ray images of the plasma show that the axial velocity of the plasma outflowing through the anode aperture is comparable with the velocity of radial plasma compression and, for tungsten ions, can reach a value corresponding to an energy of 100 keV. The experimental data indicate that the ion energy spectrum mainly forms due to the electrodynamical acceleration of the plasma and cumulative jets. A possible mechanism for the production of compact plasma formations in the course of electrodynamic plasma acceleration is discussed.

Collective ion acceleration during the decay of a high-current Z-pinch

A study is made of the Z-pinch plasma expansion after the current is switched off. Measurements were carried out in experiments on the implosion of tungsten wire arrays in the Angara-5-1 facility. It is found experimentally that, at a distance of 2 m from the pinch, the ion velocity in the expanding Z-pinch plasma is about (2.5–4.0) × 107 cm/s, which substantially exceeds the thermal velocity of tungsten ions. A model describing the plasma expansion process is proposed that is based on the ambipolar acceleration mechanism. The results of numerical simulations are compared with the experimental data.

Investigation of the dynamic of an expanding laser plume by a shadowgraphic technique

The new generation of EUV sources for lithography, based on a high current z-pinch, exploits the laser ablation of a Sn target for triggering of a discharge and delivery of working material. The dynamic of the Sn plume expansion during the first 120 ns, which strongly affects the later behavior of z-pinch was investigated by a shadowgraphic technique. Radiation in a spectral range from 18 to 20 nm was used for detection of shadow images of the Sn plume because 20 nm radiation is absorbed by the inner shells of neutrals and first ions. Thus, the probing beam is efficiently absorbed by the species most important in the formation and evolution of z-pinch. Images of the Sn plume were detected at 22 ns, 55 ns, 88 ns and 120 ns delays after the plume ignition. The technique enabled the observation of the dynamic of Sn species expansion within a range of 2 mm from the target surface. A software for the processing the detected images was developed. The estimated total number of ablated Sn neutrals and first ions varied from ∼ 2–4 × 10 14 for intensities of the focused ablating pulse in the range 8 × 10 8–10 10 W/cm 2. The experimentally detected dynamic of Sn plume expansion and total number of ablated Sn species coincide reasonably with simulated data.

The formation of metallic plasmas in transient capillary discharges at high current

We report observations of the formation of a metallic plasma in a high aspect ratio z-pinch confined within a ceramic capillary. A series of experiments on different capillary geometries was undertaken in which titanium metal rings were used to promote the formation of a titanium plasma through preferential ablation. In an initial vacuum a titanium seed plasma is formed in the hollow cathode (HC) volume by a low energy laser spark. This pre-ionizing plasma is assisted in its expansion into the z-pinch volume by the electron beams generated by a pre-ionizing discharge in the capillary, due to the HC effect. Further intense e-beam activity occurs on applying the main driver current to the capillary electrodes before the discharge impedance abruptly drops to give rise to an ensuing high current z-pinch. A segmented titanium ring structure within the capillary promotes metal ablation. The discharges are performed in tubes of 60 to 110 mm length and 3 and 5 mm effective internal diameter. The main discharge current is provided from a small pulsed power switched coaxial line, at up to 150 kA. The generator may be configured to deliver two different rates of current rise and this is found to have a significant effect on the plasma dynamics. The plasma properties are obtained from observations of the axial x-ray emission. The diagnostics used are filtered Si diodes, filtered time-resolved multi-pinhole camera images and the time resolved soft x-ray spectrum from 3 to 20 nm. While a single species metal plasma is not obtained, a very significant proportion of Ti is achieved in the higher rate of current rise configuration. The fraction of Ti diminishes for the longest length discharges and for the larger diameter tube diameter, as does the observed z-pinch uniformity. There is a weak dependance of the electron temperature with tube geometry, but the plasma density falls substantially in the longer discharges. This coincides with diminished effectiveness of the transient HC.

Effect of deposited energy on the structure of an exploding tungsten wire core in a vacuum

The experiments demonstrate the full range of transformations of an exploding tungsten wire core from a solid state to total vaporization. These states are correlated with the value of deposited energy before voltage breakdown. If the deposited energy is less than the solid-state enthalpy, the wire remains solid. If the deposited energy is between the solid- and liquid-state enthalpy, the wire disintegrates into solid macroscopic-sized pieces. If the voltage breakdown happens during the liquid state, the wire expands. In this case, the expansion velocity of the wire (0.1–1km∕s) is almost a linear function of the deposited energy. The expanding wire core is homogeneous for a deposited energy more than 4eV∕atom and nonhomogeneous (100–200 μm scale “spots”) for deposited energy less than 4eV∕atom. For homogeneous expansion, the wire core consists mainly of hot liquid microdrops of submicron size [G. S. Sarkisov, P. V. Sasorov, K. W. Struve et al., J. Appl. Phys. 96, 1674 (2004)]. For deposited energy higher than atomization enthalpy, the wire core transforms into the gas-plasma state. The linear dependence between deposited energy and expansion velocity for W wires was demonstrated. The data presented are important for the optimization of the ablation rate of wire arrays in modern high-current Z-pinch installations.

Plasma pinch for final focus and transport

Adiabatic plasma lens and Z-pinch channel transport represent attractive alternatives for the final transport of Heavy-Ion Fusion (HIF) beams to target. Production of stable, reliable, precisely timed Z-pinches is a first step to establish this method of channel transport for HIF. Stable Z-pinches at currents greater than 30 kA over a distance of 400 mm were routinely produced at 3–10 Torr. The technique uses four distinct steps: (1) laser ionization; (2) laser initiated resistor; (3) prepulse Z-pinch; and (4) high-current Z-pinch. The time interval between laser trigger and main-bank spark-gap trigger is controllable to less than 10 ns, limited by the firing characteristics of the spark gap. Optical channel diameters measured with a gated TV camera and correlated with a current probe are approximately those needed for transport in fusion chamber. No large or small scale instabilities were observed before the first current peak. A symmetric two-sided return path had a stable target interaction, even with inductively unbalanced currents. As expected, a single return path, 90° to a single-pinch channel had unstable alignment on the target, due to higher magnetic pressure on the inside of the 90° bend.

Quasi-steady processes of a high current Z-pinch

Quasi-steady states of an isolated high current Z-pinch are investigated analytically using two-temperature equations averaged in space. Some characteristic processes — a steady compression process etc. — are given. A new explanation for the results of the laser initiated gas-embedded Z-pinch experiments is also given.