Magnetic reconnection is a ubiquitous process in plasma physics, driving rapid and energetic events such as coronal mass ejections. Reconnection between magnetic fields with arbitrary shear can be decomposed into an anti-parallel reconnecting component and a non-reconnecting guide-field component, which is parallel to the reconnecting electric field. This guide field modifies the structure of the reconnection layer and the reconnection rate. We present results from experiments on the MAIZE pulsed-power generator (500 kA peak current, 200 ns rise time), which use two exploding wire arrays, tilted in opposite directions, to embed a guide field in the plasma flows with a relative strength b≡Bg/Brec=0, 0.4, or 1. The reconnection layers in these experiments have widths that are less than the ion skin depth, di=c/ωpi, indicating the importance of the Hall term, which generates a distinctive quadrupolar magnetic field structure along the separatrices of the reconnection layer. Using laser imaging interferometry, we observe quadrupolar structures in the line-integrated electron density, consistent with the interaction of the embedded guide field with the quadrupolar Hall field. Our measurements extend over much larger length scales (40di) at higher β (∼1) than previous experiments, providing an insight into the global structure of the reconnection layer.

In this article, we present experimental tests of a hybrid X-pinch loaded with a deuterated polyethylene fiber (CD2). These experiments were performed on the 1-MA, 100-ns MAIZE linear transformer driver (LTD). The purpose of these experiments was to investigate the properties of CD2 hybrid X-pinches as fast, spatially localized neutron sources. To our knowledge, these are the first experimental tests of a CD2 X-pinch in a hybrid configuration reported in the literature as well as the first tests of a CD2 X-pinch in general on a low-impedance LTD such as MAIZE ( 0.16 Omega ). The resulting neutron production was found to be highly correlated with X-ray emission peaks, to less than or similar to 10 ns, with a production duration of typically 15-20 ns. In the limited parameter sweep performed, the average yields were on the order of 10(7) neutrons, while the maximum yield obtained was as high as 1.4x10(8) neutrons. Such yields are comparable to those obtained from a gas-puff z-pinch on MAIZE; however, the CD2 hybrid X-pinch provides a more localized source and requires less deuterated material.

The Z-pinch Network US (ZNetUS) is a consortium of researchers from academia, national laboratories, and private industry, dedicated to advancing pulsed magnetic science, technology, and high energy density physics for energy and national security applications with a special focus on creating the pipeline of next-generation scientific leaders. The National Nuclear Security Administration (NNSA) has recently established a pilot User Facilities program through ZNetUS. This initiative represents a significant stride in fostering academic-led collaborations aimed at enhancing the field of pulsed magnetic science and technology (PMS&T). ZNetUS successfully launched its User Facilities program in 2024 awarding time on the User Facilities. Below is a research summary for the first full year of campaigns, and some guidelines on how to start collaborations and apply for time at the ZNetUS.

The Recirculating Planar Crossed-Field Amplifier (RPCFA) is a high power microwave amplifier. The RPCFA is initially zero drive stable and exhibits 11.6 dB gain with a 400 kW, 3.05 GHz input signal. By changing the AK gap, the RPCFA acts as an oscillator or a driven oscillator when an input signal is present. The experimental and simulated operating parameters and microwave output characteristics will be discussed.

A gas-puff z-pinch experimental platform has been developed for the 0.5-1-MA, 100-250-ns MAIZE pulsed power facility at the University of Michigan. The experiment consists of a nozzle and fast-valve assembly, which is integrated into the pulsed power circuit and forms a gas load in the center of the pulsed power device. The capacitors that form the pulsed power device discharge through the gas, forcing it to pinch on axis. Such a gas-puff z-pinch is afflicted by various instabilities, the mitigation of which is achieved by imploding multiple concentric shells of gas with increasing gas density toward the center of the pinch and imploding high mass number gases onto low mass number gases. These constraints suggested the development of a triple-nozzle system with an outer shell, inner shell, and central jet. A voltage-driven thin-shell model was used to inform the design of the gas-puff nozzles' radii and gas pressures in the fast valve. The hardware was developed based on this point design. The MAIZE transmission lines were redesigned to accommodate the new hardware. Systems that support the gas-puff experiment include a gas manifold that supplies the nozzles with gas; a driver that pulses the valve to opened and closed states; and a logic circuit that provides a signal if and only if the gas-puff load successfully forms, to trigger MAIZE and the diagnostics. These were all constructed, tested, and integrated into the experiment. Additional diagnostics were also developed and fielded: a 2-D interferometer, a four polycrystalline diamond (PCD) detector array with Ross filter pairs, and neutron bubble detectors. Characteristic results from the first z-pinch experiments conducted with this gas-puff system are presented. The system demonstrates an x-ray energy output of up to 720 +/- 50 J per pulse and a neutron output of up to (4.9 +/- 0.5) x 10(8) neutrons per pulse. Notably, this system has enabled shot rates of over 30 z-pinch experiments per day on MAIZE.

An X-pinch load driven by an intense current pulse (>100 kA in ∼100 ns) can result in the formation of a small radius, runaway compressional micro-pinch. A micro-pinch is characterized by a hot (>1 keV), current-driven (>100 kA), high-density plasma column (near solid density) with a small neck diameter (1–10 µm), a short axial extent (<1 mm), and a short duration (≲1 ns). With material pressures often well into the multi-Mbar regime, a micro-pinch plasma often radiates an intense, sub-ns burst of sub-keV to multi-keV x rays. A low-density coronal plasma immediately surrounding the dense plasma neck could potentially shunt current away from the neck and thus reduce the magnetic drive pressure applied to the neck. To study the current distribution in the coronal plasma, a Faraday rotation imaging diagnostic (1064 nm) capable of producing simultaneous high-magnification polarimetric and interferometric images has been developed for the MAIZE facility at the University of Michigan. Designed with a variable magnification (1–10×), this diagnostic achieves a spatial resolution of ∼35 µm, which is useful for resolving the ∼100-μm-scale coronal plasma immediately surrounding the dense core. This system has now been used on a reduced-output MAIZE (100–200 kA, 150 ns) to assess the radial distribution of drive current immediately surrounding the dense micro-pinch neck. The total current enclosed was found to increase as a function of radius, r, from a value of ≈50±25 kA at r ≈ 140 µm (at the edge of the dense neck) to a maximal value of ≈150±75 kA for r ≥ 225 µm. This corresponds to a peak magnetic drive pressure of ≈75±50 kbar at r ≈ 225 µm. The limitations of these measurements are discussed in the paper.

Presented is a platform for studying instability development and magnetic flux compression in a low-density plasma as the plasma implodes onto a dense cylindrical target. This platform, developed for the MAIZE pulsed power facility at the University of Michigan, utilizes the plasma from an annular gas-puff z -pinch to compress a preapplied axial magnetic field onto a central cylindrical rod. For the experiments presented, MAIZE supplied a driving current pulse that rose from 0 to 500 kA in approximately 150 ns. Images captured with fast framing cameras show that steep helical striations formed in the low-density plasma when the axial field (0.25-0.75 T) was applied. Measurements of the axial field during the implosion indicate a magnetic flux compression efficiency of nearly 50% (relative to an ideal flux compression model where an imploding thin shell with zero resistivity is assumed). The experiments presented are relevant to the magnetized liner inertial fusion (MagLIF) program on the Z facility at Sandia National Laboratories, where low-density plasma in the facility's power feed is likely compressed onto the outer surface of the dense MagLIF liner, potentially seeding instability structure in the liner.

X-ray imaging indicates magnetized liner inertial fusion (MagLIF) stagnation columns have a complicated quasi-helical structure with significant variations in x-ray brightness along the column. In this work, we describe MagLIF experiments aimed at controlling these stagnation structures by varying the initial liner geometry and composition. First, by varying the initial aspect ratio of the liner, we demonstrate a change in the stagnation structures that is consistent with helical magneto Rayleigh–Taylor (MRT) instabilities feedthrough from the outer-to-inner surfaces of the liner. Second, to minimize the seed for such instabilities, we incorporate a dielectric coating on the outer surface of the beryllium liner, which has previously been shown to reduce the growth of the electrothermal instability, a likely seed for MRT growth. Using this coating, we achieve a stagnation column with significantly reduced helical structure and axial variation in x-ray brightness. We discuss how this coating changes the evolution of structures through stagnation along with the spatial uniformity of neutron production. Finally, we show that these more uniform stagnations also result in improved reproducibility in stagnation temperatures and primary DD neutron yield.

Performance of magnetized liner inertial fusion (MagLIF) experiments is highly dependent on transport processes including magnetized heat flows and magnetic flux losses. Magnetohydrodynamic simulations used to model these experiments require a choice of model for the transport coefficients, which are the constants of proportionality relating driving terms, such as temperature gradients and currents, to the associated heat and magnetic field transport. The coefficients have been the subject of repeated recalculation using various methods throughout the years. Using a semi-analytic MagLIF model [McBride and Slutz, Phys. Plasmas 22, 052708 (2015)], we compare models for the transport coefficients provided by Braginskii [Reviews of Plasma Physics, edited by M. A. Leontovich (Consultants Bureau, New York, 1965), Vol. 1, p. 205], Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], Ji and Held [Phys. Plasmas 20, 042114 (2013)], Davies et al. [Phys. Plasmas 28, 012305 (2021)], and Sadler et al. [Phys. Rev. Lett. 126, 075001 (2021)]. The choice of model modifies magnetic-flux losses caused by the Nernst thermoelectric effect and thermal conduction losses. We present simulated results from parameter scans conducted in order to compare the effects of the different models on parameters of interest in MagLIF. In some regions of parameter space, discrepancies of up to 38% are found in integrated quantities like the fusion yield. These results may serve as a guide for experimental validation of the various models, particularly as laser preheat energies and initial axial field strengths are increased on MagLIF experiments.

We report on the results of point-projection ion deflectometry measurements from a mid-size university z-pinch experiment. A 1 MA 8 kJ LTD generator at the University of Michigan (called MAIZE) drove a hybrid x-pinch (HXP) with a deuterated polyethylene fiber load to produce a point-like source of MeV ions for backlighting. In these experiments, 2.7 MeV protons were generated by DD beam-target fusion reactions. Due to the kinematics of beam-target fusion, the proton energies were down-shifted from the more standard 3.02 MeV proton energy that is released from the center-of-mass rest frame of a DD reaction. In addition to the 2.7 MeV protons, strongly anisotropic beams of 3 MeV accelerated deuterons were detected by ion diagnostics placed at a radial distance of 90 mm from the x-pinch. Numerical reconstruction of experimental data generated by deflected hydrogen ion trajectories evaluated the total current in the vacuum load region. Numerical ion-tracking simulations show that accelerated deuteron beams exited the ion source region at large angles with respect to the pinch current direction.

Power flow studies on the 30-MA, 100-ns Z facility at Sandia National Laborat ories (SNL) have shown that plasmas in the facility’s magnetically insulated transmission lines (MITLs) can result in a loss of current delivered to the load. 1 During the current pulse, thermal energy deposition into the electrodes (ohmic heating, charged particle bombardment, etc.) causes neutral surface contaminants layers (water, hydrogen, hydrocarbons, etc.) to desorb, ionize, and form plasmas in the anode-cathode (AK) gap. 2 Shrinking typical ele ctrode thicknesses (~1 cm) down to that of thin foils (5−200 µm) produces observable amounts of plasma on smaller pulsed power drivers (≤1 MA). 3 We suspect that as the electrode material bulk thickness decreases relative to the skin depth of the current pulse (50−100 µm for a 100−500-ns pulse in aluminum), the thermal energy delivered to the neutral surface contaminant layers increases, and thus more surface contaminants desorb from the current carrying surface.

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.

The transition from amplifier to oscillator of the Recirculating Planar Crossed-Field Amplifier (RPCFA) is examined in simulation and experiment. Initially, the RPCFA is zero-drive stable and operates as a high power amplifier with an input signal. By changing the anode-cathode gap, the RPCFA can exhibit oscillations. We explore the cold-tube and beam-loaded device characteristics that cause the transition to oscillation.

This study is to develop a diagnostic suite for studying neutron production in gas-puff z-pinch experiments on the Michigan Accelerator for Inductive Z-Pinch Experiments (MAIZE) [1] . Of particular interest is measuring neutron yields from DD fusion reactions. Neutron production has been demonstrated recently on MAIZE with bubble detectors, but more accurate measurements of neutron yield are needed. We obtain accurate yield measurements through the use of scintillation techniques, where ionizing radiation is detected by the light produced in a scintillator material. Most scintillation materials convert the kinetic energy of charged particles into detectable light, where the conversion is linear, and the light yield is proportional to the deposited energy [3] . The diagnostic in this study is a beryllium (Be) probe detector, where neutrons activate Be in a 9 Be(n, a) 6 He reaction, and the subsequent decay of 6 He is observed to infer neutron yield [2] . Beta electrons from the decay of 6 He deposit energy in the scintillator and light is emitted and collected by a PMT.

Helical magneto-Rayleigh-Taylor instability (MRTI) structures have been observed in z-pinch-driven liner implosion experiments with a pre-imposed axial magnetic field. We show that the formation of these helical structures can be described by a Hall magnetohydrodynamical (HMHD) model. We used the 3D extended magnetohydrodynamics simulation code PERSEUS (which includes Hall physics) [C. E. Seyler and M. R. Martin, Phys. Plasmas 18, 012703 (2011)] to study these helical instabilities and show that a Hall interchange instability in low-density coronal plasma immediately surrounding the dense liner is responsible for producing helically oriented effects in the magnetic field and current density within the coronal layer. This seeds the helical pitch angle of the MRTI even when other proposed helical seeding mechanisms are either not present in the experiments or not accounted for in the simulations. For example, this mechanism does not require low-density power-feed plasmas to be swept in from large radius or the development of electrothermal instabilities. The Hall Instability is thus a new, independent explanation for the origin of the helical instabilities observed in axially premagnetized liner experiments. Simulation results supporting this mechanism are presented.