We report on new, portable X-pinch systems presently under development at Imperial College for probing dense plasmas. Presently 3 drivers have been built, each weighing ~50kg, and capable of driving currents >100kA. With a simple X-pinch load ~100mJ of radiation are emitted in ~1ns duration from a spot size of a few microns. The emission spectra depends on wire material, typically with strong emission in the k-lines, along with a broadband continuum stretching to many 10s of KeV. Radiography, X-ray absorption spectrometry and X-ray diffraction diagnostic tests are discussed, along with the first results utilizing X-ray polycapillary lenses with an X-pinches source to increase flux on target and enable large standoff distances.

We summarise existing results and future avenues of research from a novel experimental platform [1] fielded on the MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time). This platform uses the x-ray pulse emitted from a wire array z-pinch to drive plasma ablation from a target. The radiatively driven outflow has a uniform (quasi-1D) structure and expands into the ambient magnetic field produced by the z-pinch.

The Pulsed Power Plasmas (P3) group at UC San Diego develops experimental and diagnostic platforms for a range of HEDP and related plasma studies including inertial fusion, laboratory astrophysics and basic plasma physics. These studies are supported by simulation work carried out in collaboration with academic, national laboratory and private partners. Pulsed power drivers focus on $1\mu\mathrm{s}$ timescale devices, where the relatively slow varying plasma parameter can be studied in detail over large $(\text{mm}^2)$ volumes. Shocks generated by supersonic and magneto-supersonic flows can be designed to be stationary in the laboratory frame, and jet and flow systems are driven for timescale many times the hydrodynamic scale.

The dynamics of high-energy-density plasmas are dominated by the formation of instabilities. These can be seen on at all scales, from the structure of proto-stellar jets and nebulae, to the inertial confinement fusion experiments where instabilities can mix cold, dense, high Z plasma into fusion fuel significantly reducing yield. Measuring how the hydrodynamic instabilities evolve is crucial to providing quantitative comparison to theory and simulations, yet many experiments are limited to exploring relatively small region of parameter space in Mach and Atwood numbers, or provide only a few measurements per experiment, requiring control of the initial conditions (ICs).

High voltage, nanosecond risetime pulses are widely used for the triggering of high current switches in pulsed power facilities, however many of the generators used to produce these pulses are either no longer available (for example PT55s) or costly and complex. We present research into a modern, compact spiral generator using charging voltages of only $\sim$ few kV and solid state input switches to produce fast rising pulses of >>50kV. Through experiment and modelling we have explored how the pulses are formed within the spiral, why a high speed input switch is required, how the geometry of the spiral dictates its output characteristics, and the effects of different loads.

X-pinches, formed by driving intense current through the crossing of 2 or more wires, provide an excellent platform for the study of “micro-pinches” due to their propensity to generate a single micro-pinch at a predetermined location in space (i.e., where the wires cross) [1], [2]. Ideally, micro-pinches are areas of run-away compression to very small radii $(\sim 1\ \mu \mathrm{m})$ leading to pressures on the order of ~1 Gbar for currents on the order of ~0.1 MA. However, the fraction of the total current that is driven through the dense micro-pinch plasma at small radii versus that being shunted through the surrounding coronal plasma at larger radii is not well known. To allow for the study of X-pinches and their current distribution on the 1-MA MAIZE facility, a Faraday rotation imaging diagnostic (1064 nm) [3], as well as a corresponding modular load hardware, were developed. Presented is the status of these developments including preliminary experimental results characterizing X-pinches on the MAIZE LTD.

To better understand current losses in the MITL of high-power pulsed power machines, experiments may be conducted at scale in smaller facilities. However, on typical 1 MA peak current pulsed power drivers, it is difficult to produce the required current densities and magnetic fields. In this poster, we present a novel experiment that is being tested on the MAGPIE driver at Imperial College. Called the “hairpin”, this geometry uses small wires of circular cross-section bent into slightly inductive loops. Wire bending is inexpensive, so manufacturing costs are dramatically reduced compared to stripline experiments. In addition, the curvature of the wire cross-section provides field enhancement at the apex of the curve, making even higher magnetic and electric field strength attainable. Lastly, the inductance of the loop can easily be varied, providing precise tuning of the electric and magnetic field strengths in the experiment. Simulations using the COMSOL multiphysics software are presented, and compared with similar simulations using the GORGON code. These indicate that magnetic fields from 70 T to 300 T and electric fields from 30 MV/m to 650 MV/m can be produced with this geometry on MAGPIE. Preliminary results from an experimental campaign on MAGPIE are then presented and compared with the simulations.

Underwater electrical wire explosion (UEWE) has been demonstrated to be a robust approach in the research of matter at extreme conditions, the main goal of high energy density physics (HEDP). Indeed, applying pulse generators with stored energy of several kJ allows one to achieve $\geq 10^{8}\mathrm{J}/(\text{kg}\times \mathrm{s})$ energy density deposition rate, pressure of $> 10^{9}$ Pa, and temperature of several eV. It was shown that UEWE is accompanied by rapid phase transitions of wire material resulting in the formation of a non-ideal, high-resistivity plasma characterized by fast-rising thermal instabilities, allowing conductivity research of different materials at extreme conditions. Additionally, we demonstrated that a planar shock, generated by the explosion of planar wire arrays, can efficiently (~12% energy transfer) accelerate targets. Moreover, the generation of supersonic (~4.5 km/s) water jets by the explosion of a conical wire array was demonstrated. The latter can be used for sub-Mbar pressure formation when interacting with a target. These results show great promise when considering scaling experiments into more powerful pulse generators. Ongoing research of UEWE employs different diagnostics such as high current and voltage measurements, shadow frame and streak imaging, X-ray radiography, and visible spectroscopy. Experimental results are compared to one-and two-dimensional hydrodynamic and magneto-hydrodynamic simulations, which recreate key experimental results, providing additional insight into the complex process occurring during UEWE. In this presentation selected results from recent advancements in studying and applying the aforementioned processes in the field of UEWE to further understanding HEDP will be discussed.

The implosion of fast, convergent shock waves driven via the electrical explosion of cylindrical wire arrays embedded in insulator offers a highly efficient method of generating extreme pressures. At low currents (~30kA) the increased density on axis was directly observed at the ESRF synchroton; at higher currents - up to 2.5MA on the Cepage generator at First Light Fusion - the implosion dynamics imply pressures >Mbar exist in warm dense plasma on axis. How this process scales to currents >5MA is unclear - a limit could exist on the speed at which the shockwaves are initially projected from the wires, set by the rate of energy deposition into the wires.

X-pinches, formed by driving intense current through the crossing of 2 or more wires, provide an excellent platform for the study of "micro-pinches" due to their propensity to generate a single micro-pinch at a predetermined location in space (i.e., where the wires cross) [1] , [2] . Ideally, micropinches are areas of run-away compression to very small radii (~1 µm) leading to pressures on the order of ~1 Gbar for currents on the order of ~0.1 MA. However, the fraction of the total current that is driven through the dense micro-pinch plasma at small radii versus that being shunted through the surrounding coronal plasma at larger radii is not well known. To allow for the study of micro-pinches and their current distribution on the 1-MA MAIZE facility, a Faraday rotation imaging diagnostic (1064 nm) [3] , as well as a corresponding modular X-pinch load hardware, were developed. Presented is the status of these developments including preliminary experimental results characterizing X-pinches on the MAIZE LTD.

Magnetized Liner Inertial Fusion (MagLIF) at Sandia National Laboratories involves a laser preheating stage where a few-ns laser pulse passes through a few-micron-thick plastic window to preheat gaseous fusion fuel contained within the MagLIF target. Interactions with this window reduce heating efficiency and mix window and target materials into the fuel. A recently proposed idea called "Laser Gate" involves removing the window well before the preheating laser is applied. In this article, we present experimental proof-of-principle results for a pulsed-power implementation of Laser Gate, where a thin current-carrying wire weakens the perimeter of the window, allowing the fuel pressure to push the window open and away from the preheating laser path. For this effort, transparent targets were fabricated and a test facility capable of studying this version of Laser Gate was developed. A 12-frame bright-field laser schlieren/shadowgraphy imaging system captured the window opening dynamics on microsecond timescales. The images reveal that the window remains largely intact as it opens and detaches from the target. A column of escaping pressurized gas appears to prevent the detached window from inadvertently moving into the preheating laser path.

We present experimental measurements of a pulsed plasma gun, using two-colour imaging laser interferometry and spatially resolved Thomson scattering. Interferometry measurements give an electron density n(e) approximate to 2.7 x 10(17) cm(-3) at the centre of the plasma plume, at 5 mm from the plasma gun nozzle. The Thomson scattered light is collected from two probing angles allowed us to simultaneously measure the collective and non-collective spectrum of the electron feature from the same spatial locations. The inferred electron densities from the location of the electron plasma waves is in agreement with interferometry. The electron temperatures inferred from the two spectra are not consistent, with T-e approximate to 10 eV for non-collective scattering and T-e approximate to 30 eV for collective scattering. We discuss various broadening mechanisms such as finite aperture effects, density gradients within the collective volume and collisional broadening to account for some of this discrepancy. We also note the significant red/blue asymmetry of the electron plasma waves in the collective scattering spectra, which could relate to kinetic effects distorting the distribution function of the electrons.

Cylindrical copper wire array explosions were carried out in de-ionized water, sodium polytungstate solution, nitromethane, and polyester in order to obtain high energy density conditions in the vicinity of implosion using the generated converging shock waves. The use of different materials in which the array is immersed can contribute to this goal with higher density resulting in higher shock velocities and possible combustion. The generated shock waves were captured by a framing and a streak camera, and shock velocities were calculated and compared. The pressure behind the shock front was calculated using the known hydrodynamic relations (for water, polytungstate, and polyester) and compared to two-dimensional hydrodynamic simulations coupled with the equations of state (for water and polyester). It was shown that despite lower shock wave velocity in polytungstate solution than in water, the pressures generated are similar in both materials. In polyester, both shock velocities and generated pressures are 2–4 times higher than in water. It was also shown that it is possible to carry out these explosions in a solid which has several advantages compared to liquids, such as not relying on waterproof systems and easier transportation.

We present the measurements of the development of striation like instabilities during the electrical driven explosions of wires in a water bath. In vacuum based wire explosion experiments, such instabilities have long been known. However, in spite of intense research into the explosion of wires in liquids, the development of these instabilities has either not been observed or has been assumed to play a minor role in the parameters of the exploding wire due to the tamping of the wire's explosion. Using synchrotron based multiframe radiography, we have seen the development of platelike density structures along an exploding copper wire. Our measurements were compared to a 2D magnetohydrodynamics simulation, showing similar striation formation. These observed instabilities could affect the measurements of the conductivity of the wire material in the gas-plasma state—an important parameter in the warm dense matter community. The striations could also act as a seed for other instabilities later in time if the wire is in a dense flow of material or experiences a shock from an adjacent wire—as it would do in experiments with arrays of wires.

The objectives of this tutorial are as follows: 1) to help students and researchers develop a basic understanding of how pulsed-power systems are used to create high-energy-density (HED) matter; 2) to develop a basic understanding of a new, compact, and efficient pulsed-power technology called linear transformer drivers (LTDs); 3) to understand why LTDs are an attractive technology for driving HED physics (HEDP) experiments; 4) to contrast LTDs with the more traditional Marx-generator/ pulse-forming-line approach to driving HEDP experiments; and 5) to briefly review the history of LTD technology as well as some of the LTD-driven HEDP research presently underway at universities and research laboratories across the globe. This invited tutorial is part of the Mini-Course on Charged Particle Beams and High-Powered Pulsed Sources, held in conjunction with the 44th International Conference on Plasma Science in May of 2017.

In Magnetized Liner Inertial Fusion (MagLIF), pressurized fuel inside of a cylindrical metal tube (or “liner”) is preheated with a laser pulse. The laser enters the pressurized fuel region through a thin laser entrance window (LEW). The LEW contains the pressurized fuel inside of the liner until the few-ns preheating laser pulse is applied, which ablates the LEW and preheats the fuel. Energy losses are thought to occur at the laser entrance window (LEW) as a result of laser-plasma interactions (LPI). Additionally, simulations are presently unable to reliably model the LPI losses. 1 To reduce energy losses and computational uncertainties, the LEW could be weakened and removed very early in time, well before the preheating laser pulse arrives at the LEW. 2 This general concept of removing the LEW very early in time is referred to as “Laser Gate.”2 One proposed implementation of Laser Gate, which we are working on at the University of Michigan, is to break the LEW very early in time by driving an electrical current through a thin wire that is wrapped around the perimeter of the LEW. 2 The electrical current heats and melts the perimeter of the LEW, allowing the fuel pressure to push open the LEW. As the LEW is broken, it opens away from the contained fuel and out of the laser path. Before a significant amount of fuel has time to escape the liner, the preheating laser pulse is applied. Doing this successfully should reduce fuel-window mixing and LPI in MagLIF. For our experiments at UM, the pulsed electrical current is driven through the thin wire by a 13-kV mini-pulser. Additionally, a laser backlighting system is being developed to image the dynamics of the LEW as it opens. We will report on our first experimental tests of this implementation of Laser Gate.