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The gas-puff Z-pinch is a well-known, efficient source of X-rays and/or neutrons, in which a cylindrical load is imploded by a pulsed-power driver due to the force arising from an applied axial current interacting with a self-generated azimuthal magnetic field. It is susceptible to the magneto-Rayleigh-Taylor instability (MRTI), which must be mitigated to achieve sufficient energy density, i.e., compression. Density tailoring, axial pre-magnetization, and increasing liner resistivity have been shown independently to be effective approaches. Here, we present 2-D radiation-MHD simulations using the HYDRA code [1] of axially-pre-magnetized multi-shell gas-puffs – one or two annular "liners" of Ne, Ar, or Kr, and a central D jet – that predict the mitigation from these approaches are additive: the axial magnetic field (Bz0) required to stabilize a Ne/D implosion is reduced from 0.7 T to 0.3 T by the addition of a second inner liner, and is further reduced by changing the outer liner to more-resistive Ar or Kr. Furthermore, the results suggest an Ne or Ar inner liner provides greater mitigation via snowplow stabilization than a Kr inner liner, as well as mitigation of ion thermal conduction losses from the fuel, the dominant loss mechanism at the 850-kA level. We conclude with a discussion on the scalability of these phenomena to 20 MA, at which level effects such as radiative cooling and fuel mixing may become more relevant.

The Dense Plasma Focus (DPF) is a Z-pinch configuration where coaxial electrodes channel a dynamic plasma sheath along the anode, resulting in a hot dense pinch near the anode tip. DPF is capable of producing X-rays, energetic ions, and high intensity, fast neutron pulses. Ongoing experiments using a 4.4 kJ Mather-type DPF exploring the role of anode geometry will be presented, with a focus on several geometries highlighted in recent theoretical works 1 , 2 , including curved and flat anodes with and without a hollow center. The convergence of plasma on axis is heavily influenced by the relationship between the residual axial motion of the plasma sheath relative to the inward driving force, which is primarily affected by the anode geometry and operating fill pressure. Trends in neutron yield measured by a calibrated Be activation detector will be presented alongside laser probing diagnostics and high energy X-ray sensitive photodiode measurements.

The deuterium-fill Dense Plasma Focus (DPF) is a Z-pinch configuration that produces energetic ions, X-rays, and neutrons from a high-temperature and high-density plasma pinch. There have been limited studies that consider the impact of the insulator length on the resulting pinch quality and neutron production. Experiments were conducted on a 4.4 kJ (250 kA, 21 kV) Mather type DPF 1 with laser probing diagnostics and a Be-activation detector for three different insulator sleeve lengths. Here, we report the results of experiments to optimize the neutron yield as a function of insulator sleeve length and fill pressure. The results show that the insulator length plays an important role in the dynamics, including pinch timing and neutron yield: increasing the insulator length reduces the effective anode length and thus affects the optimal fill pressure.

The gas puff Z-pinch 1 is a magnetic direct-drive plasma compression scheme with applications as an efficient X-ray or neutron source and for research on the fundamental physics of dense plasmas. Presented here are results of gas puff Z-pinch experiments on the CESZAR driver 2 (500 kA, 160 ns) with an annular liner imploding onto an on-axis target, where one or both species is D2. We investigate the effects of load material (D2, Ne, Ar, or Kr) on implosion dynamics, including stability and energy coupling, and on pinch performance. We show via self-emission and laser imaging that the inclusion of a central target jet improves pinch stability, and we discuss correlations between gas species and stability in liner-on-target implosions. Magneto-hydrodynamic simulations are used to infer values of plasma kinetic and internal energy, which are compared with experimental estimates. Pinch performance is quantified by measuring X-ray and neutron yield. Finally, we show that pinch reproducibility can be improved by pre-ionizing the gas before the main current pulse.

In many Z-pinch experiments, the magneto Rayleigh-Taylor instability and other MHD instabilities are potentially disruptive to the pinch. It has been demonstrated that multi -shell Z- pinch loads and an externally-applied axial magnetic field can mitigate these instabilities1. An external magnetic field has been applied in Staged Z-pinch2 (SZP), where a high-atomic-number gas liner (Ar or Kr) implodes onto a deuterium target in cylindrical geometry.

Recent experiments at the Nevada Terawatt Facility at UNR show evidence of uniform compression of a deuterium plasma target compressed by a high-Z, Argon or Krypton gas-puffed liner. Pinch stability is improved by seeding the implosion with a 0.1-0.2 T axial magnetic field. Implosion dynamics and stagnation conditions are also studied computationally with the radiation-MHD code MACH2, using in itial conditions similar to those in the experiment. Simulations show that magnetic field diffuses through the outer shell and piles up at the interface providing narrow profile, high intensity current that Ohm-icly preheats the target. This secondary piston launches a shock wave in the target plasma that heats the several 100 eV. Finally, the preheated target is adiabatically compressed to stagnation. Simulations show: (a) more pronounced preheating with Kr than Ar, (b) the axial magnetic field is compressed only in the shocked target and in the liner plasma, providing greater magneto-Rayleigh-Taylor mitigation during run-in compared to the self-similar model. For typical Ar liner on D target experiments we measured neutron yield up to 2x 109 and for Kr liner, up to 9x 109.

Semi-analytic models are useful tools in performing high-level parameter scans of complicated systems, as they are more flexible than analytic models and less computationally expensive than full-fledged simulations. Such models guided early magnetized target fusion (MTF) efforts1, and have been published recently in the literature for MTF2, MagLIF3, and $\text{PLX}-\alpha$ 4. We present here a semi-analytic model for the Staged Z-pinch, a magneto-inertial concept in which a high-atomic-number cylindrical liner or gas-puff implodes onto a low-Z (e.g. H or D) target, and compare its predictions with those of the radiation-MHD codes HYDRA and MACH2.

Understanding plasma shock behavior can inform the design of fusion reactor and X-ray source concepts such as the Staged Z-pinch [1], Magnetized Liner Inertial Fusion (MagLIF) [2], and inertial confinement fusion (ICF) [3]. The cylindrical or spherical geometry of such concepts obscures imploding shocks from diagnostic view and complicates analysis of observations. A simpler, planar geometry eases diagnosis and comprehension of the physics underlying the shocks.

The Staged Z-pinch is a magneto-inertial fusion concept in which compression of the target plasma, deuterium (D) or deuterium-tritium (DT) is driven by two mechanisms: inertial compression of the liner plasma, typically a high-Z gas like Kr, driven by the externally-applied JxB force, and shock compression, driven by transport of this force to the target/liner interface.

Previous Staged Z-pinch (SZP 1 experiments at the University of California-Irvine demonstrated that gas liners (or gas-puffs) can efficiently couple energy to a target plasma and implode it uniformly. In those experiments, a 1.5 MA, $1 \mu \mathrm {s}$ current driver was used to implode a magnetized, Kr liner onto a D+ target, producing ~1010 neutrons per shot. Time-of-flight data suggested that primary and secondary neutrons were produced. Recent MHD simulations 2 have suggested that liner composition is important for target shock-heating before the main adiabatic implosion and that pre-magnetization is crucial to achieve uniform implosions.A recent series of experiments were carried out to investigate implosion dynamics using Cornell’s 1 MA, 200 ns current driver COBRA with a goal to help us better understand the SZP physics and benchmark MHD codes. We used an optimized gas injector 3 composed of an annular (1 cm radius) high atomic number (e.g., Ar or Kr) gas-puff and an on-axis plasma gun that delivers the ionized hydrogen target. Liner implosion velocity and stability were studied using laser shadowgraphy and interferometry as well as gated visible and XUV imaging. Target temperature and density were measured with Thomson scattering and X-ray spectroscopy. Experimental data is presented and preliminary analysis is discussed.

Previous Staged Z-pinch experiments have demonstrated that gas liners (or puffs) can efficiently couple energy to a target plasma and implode uniformly, producing plasmas in High Energy Density (HED) regimes. In these experiments, a 50 kJ, 1.5 MA, 1 μs current driver was used to implode a magnetized, Kr liner onto a D+ target, producing 1010 neutrons per shot. Time-of-flight data suggested that primary and secondary neutrons were produced.

We discuss the design and characterization of a compact gas-puff nozzle and plasma gun assembly that will be used in Staged Z-pinch experiments1, where gas liners are imploded onto an on-axis target-plasma column. Previous work on the Staged Z-pinch demonstrated that gas liners can efficiently couple the energy and produce a uniform implosion on a target-plasma.2

We report on counter-propagating plasma flows produced by two vertically opposing conical wire arrays using a compact, low inductance Linear Transformer Driver (LTD) “GenASIS” capable of producing 250 kA in about 150 ns. Laser interferometry and laser schlieren were performed with the use of a Nd:YAG 532 nm laser, with a pulse width of 5 ns. A shock wave formed by jet interaction was clearly observed and remained stationary for at least 50 ns. Interferometry data showed that the ion density of the jets prior to collision was of the order of 2×1017cm−3 and a jump in density of ∼ 5 was observed at the shock wave region. A lower limit of ∼ 100 km/s has been measured for the jet velocity. The ion mean free path has been estimated to be ∼ 12 mm, which is larger than the shock wave scale ∼ 5 mm, and hence the shock wave approaches the collisionless regime. Magnetic field advection, which can drastically modify the conditions for shock wave formation, will be discussed. Kinetic particle-in-cell modeling using LSP code has also been implemented and benchmarked against the experimental results in order to study the underlying physics of formation and evolution of the shock.