Balzhima Cikhardtova

MHD simulation codes are essential tools for improving our understanding of z-pinch implosion and stagnation. While they can provide detailed information about spatially and temporally distributed variables, achieving accurate results remains challenging even within highly stable numerical schemes and with significant computational power. In z-pinch experiments, the most common approach is to fit the integral parameters, such as implosion time, average implosion velocity, implosion mass, or, e.g., x-ray power, with the simulations. However, it is also important to try to match spatially or time-resolved variables. Here, we propose a 2D MHD simulation of a dense plasma focus to analyze the radial implosion phase. In particular, we compared the density profiles with previous density measurements on the PF-1000 apparatus. Then, we focused on the analysis of current signals in both the experiment and the simulation, in particular by comparing the time derivative of the inductance.

Pulsed-power generators concentrate electrical energy in time and space, producing plasmas with extreme properties. During the final stage of current focusing, a current-carrying column can be compressed by its own magnetic field through the pinch effect. Among various pinch configurations, the x-pinch—formed by crossing two or more wires in an x-shape—has been extensively studied as a micrometer-scale, sub-nanosecond x-ray source. Here, we explore a novel aspect of x-pinches, highlighting their potential as a point-like source of MeV protons. The x-pinch experiments were performed on the XP generator, delivering a peak current of 500 kA with a rise time of 70 ns. A hybrid x-pinch configuration, comprising two solid conical electrodes connected by a single polymer fiber, was employed. A critical requirement for reproducible acceleration of protons to MeV energies was the use of low linear-mass fibers. Using nylon and polyethylene fibers with diameters of 25–40 μm, protons with energies of up to 3.9 MeV were observed in the radial direction, i.e., perpendicular to the fiber axis. Additional source parameters, particularly the effective source size and the anisotropy of the radial emission, were characterized using various CR-39-based ion detectors. Finally, the applicability of the x-pinch as a point-like proton source was demonstrated by x-pinch-driven proton radiography of an exploding wire.

In this contribution, we present the results of a long-term study on radiofrequency and microwave electromagnetic pulse (EMP) emission, a phenomenon that is still not satisfactorily explained, performed at the PALS iodine laser system (1315 nm, 0.3 ns, up to 700 J on target). Using a comprehensive set of broadband diagnostics, including double ridged horn antennas, target current probe, along with special low-loss cables and oscilloscopes with sampling rates up to 100 GS/s, we observed an unprecedentedly broad EMP spectrum with frequencies significantly exceeding 10 GHz. Moreover, scaling experiments revealed a dependence of the spectral shape and its central frequency on the laser intensity, and this was further correlated with electron emission. This dependence indicates that in addition to the well-known influence of the eigenfrequencies of the experimental hardware (e.g., target, stalk, and chamber), processes associated with the expanding plasma can also play a dominant role, as demonstrated in this study. We believe that these new findings will not only contribute to EMP mitigation and deepen our understanding of fundamental physics, but also support high-tech applications such as EMP hardening, biomedical research, and defense technologies.

Ion acceleration in Z -pinch plasmas is traditionally linked to the axial direction of current. Here, we report the radial emission of MeV protons from a low-mass, hydrogen-containing X pinch. Proton energies up to 3 MeV are observed in a hybrid X pinch with a 30 μ m polyethylene fiber at a 400 kA peak current. The low-mass load, correlation of protons with hard x-rays, and timing of hard x-ray emission point to proton acceleration driven by current disruption following fiber disintegration. A new insight into the acceleration mechanism arises from the use of an interelectrode gap that is too short for magnetic fields to bend axially accelerated protons by π / 2 radians; thus, the observed radial emission implies a substantial radial acceleration component. The radial emission also enables X -pinch-driven proton radiography, the exceptional potential of which is demonstrated with exploding wires.

The paper presents a comparison of shots with high and low neutron yield at deuterium filling. Shots with high neutron yield are characterized by a higher energy produced hard x rays and neutrons, a larger volume of plasmoid-like compact structure, and lower plasma density in the pinched column. The discrepancy was interpreted by different magnetic energies stored in the pinched column. The model of distribution of magnetic energy in a plasmoid assumes the existence of a poloidal component of magnetic field in the plasma, the formation of compact structures with closed poloidal and toroidal current components, filamentary distribution of the current, and development of MHD instabilities along the filaments. The model meets the characteristics of observed sources of fast deuterons, such as submillimeter dimensions, various directions of path with narrow directivity, and radial and azimuthal configuration of spots. The presented mechanism of acceleration of fast deuterons is based on the model of magnetic reconnection, in which part of the disappearing magnetic field induces a strong electric field sufficient for obtaining hundreds of keV energy.

Deuterium gas-puff z-pinches are researched primarily as efficient sources of DD fusion neutrons. The first experiment with a deuterium gas jet was carried out in 1978 (Shiloh et al 1978 Phys. Rev. Lett. 40 515518). Since then, several D₂ gas-puff experiments have been performed on various pulsed-power generators. The highest, so far published, DD neutron yields of 4 × 10 13 were observed on the Z machine at Sandia National Laboratories around 2005 (Coverdale et al 2007 Phys. Plasmas 14 022706). More recently, z-pinch experiments with a plasma-shell on a deuterium gas puff were carried out on the GIT-12 higher-impedance pulsed-power generator at 3 MA currents. On GIT-12, unique results were high neutron and ion energies, which approached 60 MeV. Comparison of deuterium gas-puff experiments on different generators allows the identification of the parameters essential for optimizing neutron production. These parameters include the optimal mass, preionization, short deuterium gas-injection time, and zippering towards a cathode. Neutron yields appear to depend not only on a current, but also on other parameters of a generator, such as an impedance and the energy stored in a capacitor bank. Our conclusions regarding the optimal conditions were tested on the Hawk generator (NRL, Washington, DC). At a current of 0.7 MA, Hawk accelerated deuterons up to 15 MeV producing one neutron pulse with the yield of the order of 10¹⁰ and a broad energy spectrum in the axial and radial direction. These results show that ion acceleration mechanisms in deuterium gas-puff z-pinches could be very efficient and attractive, with a variety of potential applications in high-energy-density physics, materials science, and controlled thermonuclear fusion research.

This paper presents the filamentary structure of the pinched column in a smaller plasma focus device filled with deuterium. The deflections were observed using schlieren and differential interferometry techniques. The observed filaments have a transverse diameter of 40–200 μm, which could be interpreted based on the electric current hypothesis as local concentrations of electric current. The evolution of filaments was compared with global structures recorded by extra ultraviolet frames. These results provide a basis for considering the possibility of a filamentary composition of the poloidal current in compact structures. The model of filaments with a helical shape of electrical current may be able to explain the central narrow and dense cord in the axis of the column, the different lifetimes of the structures, and the submillimeter sources of fast electrons and ions.