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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.

The gas-puff $Z$-pinch is a well-known source of x-rays and/or neutrons, but it is highly susceptible to the magneto-Rayleigh-Taylor instability (MRTI). Approaches to MRTI mitigation include density profile tailoring, in which nozzles are added or modified to alter the acceleration trajectory, and axial pre-magnetization, in which perturbations are smoothed out via magnetic field line tension. Here, we present two-dimensional magnetohydrodynamic simulations of loads driven by an 850 kA, 160 ns driver that suggest these mitigation strategies can be additive. The initial axial magnetic field, ${B}_{z0}$, to stabilize a 2.5-cm-radius Ne gas liner imploding onto an on-axis deuterium target can be reduced from 0.7 T to 0.3 T by adding a second liner with a radius of 1.25 cm. Because MRTI mitigation tends to increasingly lower yield with higher ${B}_{z0}$, the use of a lower field is advantageous. Here, we predict a reduction in yield penalty from $g100\ifmmode\times\else\texttimes\fi{}$ with the single liner to $l10\ifmmode\times\else\texttimes\fi{}$ with a double liner. A premagnetized, triple nozzle gas puff could therefore be an attractive source for intense neutrons or other fusion applications.

A linear transformer driver (LTD) generator capable of delivering up to 0.9 MA current pulses with 160 ns rise time has been assembled and commissioned at University of California San Diego. The machine is an upgrade of the LTD-III pulser from Sandia National Laboratories, consisting of 40 capacitors and 20 spark gap switches, arranged in a 20-brick configuration. The driver was modified with the addition of a new trigger system, active premagnetization of the inductive cores, a vacuum chamber with multiple diagnostic ports, and a vacuum power feed to couple the driver to plasma loads. The new machine is called compact experimental system for $Z$-pinch and ablation research (CESZAR). The driver has a maximum bipolar charge voltage of $\ifmmode\pm\else\textpm\fi{}100\text{ }\text{ }\mathrm{kV}$, but for reliability and testing, and to reduce the risk of damage to components, the machine was operated at $\ifmmode\pm\else\textpm\fi{}60\text{ }\text{ }\mathrm{kV}$, producing 550 kA peak currents with a rise time of 170 ns on a 3.5 nH short circuit. While the peak current is scaled down due to the reduced charge voltage, the pulse shape and circuit parameters are close to the results of the cavity and power feed models but suggest a slightly higher inductance than predicted. The machine was then used to drive wire array $Z$-pinch and gas puff $Z$-pinch experiments as initial dynamic plasma loads. The evolution of the wire array $Z$ pinch is consistent with the general knowledge of this kind of experiment, featuring wire ablation and stagnation of the precursor plasma on axis. The gas puff $Z$ pinches were configured as a single, hollow argon gas shell, in preparation for more structured gas puff targets such as multispecies, multishell implosions. The implosion dynamics agree generally with 1D magnetohydrodynamics simulation results, but large zippering and magneto-Rayleigh-Taylor instabilities are observed. The CESZAR load region was designed to accommodate many load types to be driven by the machine, which makes it a versatile platform for studying $Z$-pinch plasmas. The completion of the CESZAR driver allows plasma experiments on energy coupling from LTD machines to plasma loads, instability mitigation techniques and magnetic field distributions in $Z$ pinches, and interface dynamics in multispecies implosions.

The staged Z-pinch (SZP) is a magnetoinertial fusion scheme, where a high-Z gas liner implodes onto a deuterium gas target. An accurate measurement of the initial mass distribution, both in the liner and target, is crucial to achieve the fusion-relevant conditions. This paper presents the characterization of a double-valve injector for the SZP experiment, performed on a test stand with interferometric and visible emission diagnostics. The injector produces an annular liner gas profile that is peaked at $R_{L} = 1.25$ cm, has an average full width at half-maximum $\Delta r_{L} = 0.50$ cm, and a mass density $\rho _{L} = 0.5$ – $140~\mu \text{g}$ /cm3, which is adjusted by selecting the gas species between Ar and Kr, plenum pressure, and injection timing. The target gas density is centered on the axis, has a width $\Delta r_{T} = 0.80$ cm, and a density $\rho _{T} = 0.3$ –30 $\mu \text{g}$ /cm3. The molecular deuterium can be partially ionized and accelerated out of the injector with a velocity $v_{z} > 2$ cm/ $\mu \text{s}$ by a coaxial plasma gun built into the injector.

Gas puff Z-pinch experiments with annular Ar and Ne gas shells have been conducted on the Compact Experimental System for Z-pinch and Ablation Research (CESZAR) linear transformer driver (LTD) with 500 kA current and 160 ns rise time. Here, we present results from the first systematic gas puff Z-pinch experiments using a fast ( ≤200 ns) LTD as a driver, in which we show that 7% of the stored energy in the capacitors is coupled to plasma kinetic energy as estimated via self-emission and laser schlieren images. 0D and 1D simulations—which do not allow instability growth and thus reach greater maximum average velocities—using initial conditions inferred from experimental implosion trajectories predict coupling in excess of 10% of the stored energy. The Ar and Ne implosions were comparably massed and thus achieved similar maximum kinetic energies, though the Ne pinches were more stable and the x-ray pulses were longer and produced higher yield: 2–5 ns and 0.21–0.52 J (0.15–0.37 J/cm) of Ar K-shell and 12–25 ns and 2.2–3.9 J (1.6–2.6 J/cm) of Ne K-shell, respectively. The difference in stability is most likely attributed to variations in initial conditions such as density distribution and gas breakdown initiation.

The dense plasma focus (DPF) can be an intense source of x rays, wherein the insulator sleeve strongly dictates the electrical breakdown, which subsequently affects the formation of a plasma sheath and a collapse phase. Experiments on a 25 kJ DPF (operated at 4.4 kJ) are carried out to demonstrate the influence of insulator surface morphology on the pinch structure, dynamics, and x-ray yield using a Ne fill. Two borosilicate insulators are directly compared, one with a smooth finish and the other machined with four circumferential grooves traversing the perimeter of the exterior insulator surface. Comparisons are made through same-shot imaging diagnostics of the evolving plasma sheath during breakdown, rundown, and at the pinch in addition to the time-resolved measurements of emitted x rays via filtered photodiodes. The presence of structures on the insulator sleeve reduces x-ray production across all fill pressures by a factor of 2.8 ± 2.4 on average and reduces the highest x ray producing shots by a factor of 5.5 ± 1.8. Observations of sheath asymmetry and inhomogeneity at lift-off are observed and correlated with subsequent observations of off-axis radial collapse. Taken together, this suggests that local variations in the insulator surface decrease the spatial uniformity of the sheath, leading to an azimuthally asymmetric focus, reduced electron densities, and, ultimately, degraded x-ray production.

Wire X-pinches (WXPs) have been studied comprehensively as fast ( ∼ 1 ns pulse width), small ( ∼ 1 μm) x-ray sources, created by twisting two or more fine wires into an “X” to produce a localized region of extreme magnetic pressure at the cross-point. Recently, two alternatives to the traditional WXP have arisen: the hybrid X-pinch (HXP), composed of two conical electrodes bridged by a thin wire or capillary, and the laser-cut foil X-pinch (LCXP), cut from a thin foil using a laser. We present a comparison of copper wire, hybrid, and laser-cut foil X-pinches on a single experimental platform: UC San Diego’s ∼ 200 kA, 150 ns rise time GenASIS driver. All configurations produced 1–2 ns pulse width, ≤ 5 μm soft x-ray (Cu L-shell, ∼ 1 keV) sources (resolutions diagnostically limited) with comparable fluxes. WXP results varied with linear mass and wire count, but consistently showed separate pinch and electron-beam-driven sources. LCXPs produced the brightest ( ∼ 1 MW), smallest ( ≤ 5 μm) Cu K-shell sources, and spectroscopic data showed both H-like Cu K α lines indicative of source temperatures ≥ 2 keV, and cold K α ( ∼ 8050 eV) characteristic of electron beam generated sources, which were not separately resolved on other diagnostics (within 1–2 ns and ≤ 200 μm). HXPs produced minimal K-shell emission and reliably single, bright, and small L-shell sources after modifications to shape the early current pulse through them. Benefits and drawbacks for each configuration are discussed to provide potential X-pinch users with the information required to choose the configuration best suited to their needs.

The addition of Kr dopant to a deuterium or deuterium–tritium dense plasma focus (DPF) is conventionally thought to enhance radiative cooling of the imploding sheath, resulting in a tighter pinch and, under optimized conditions, increased neutron yield [M. Krishnan, IEEE Trans. Plasma Sci. 40, 3189 (2012)]. In this work, 2D radiation magnetohydrodynamic (MHD) simulations are conducted of a DPF at peak current levels in the 2–3 MA range with Kr dopant concentrations of 0%, 0.1%, and 1.0% (by volume). Fully kinetic simulations are required to accurately model the pinch stagnation and accurately predict total neutron yield (thermonuclear + beam target), as MHD simulations cannot capture kinetic effects or beam-target neutron production. However, insights can be gained from following the evolution of the bulk dynamics of the sheath. The results show that sheath width narrows with increasing dopant concentration due to increased radiation. Thermonuclear neutron yields of ∼ 10 9 − 10 10 are observed, which is in good agreement with experimental data [E. N. Hahn et al., J. Appl. Phys. 128, 143302 (2020)] and simulations [N. Bennett et al., Phys. Plasmas 24, 021702 (2017)] that measure yields of ∼ 10 11 at ∼ 2 MA with ∼ 1% of that yield having thermonuclear origin. Scaling in excess of the conventional ∝ I 4 scaling is observed, though this should be confirmed with 3D and/or fully kinetic simulations of Kr-doped DPFs.

Experiments on a MA-class Dense Plasma Focus (DPF) device have been carried out to investigate changes in neutron production by adding moderate amounts of krypton to a deuterium fill gas. The neutron yield from Z-pinch devices, including DPFs, conventionally scales as the peak current to the fourth power. However, a dramatic drop-off from ∼I4 scaling occurs above 3 MA, which recent modeling [D. T. Offermann et al., Phys. Rev. Lett. 116, 195001 (2016)] attributed to the transition in the predominant neutron production mechanism from beam-target fusion to thermonuclear fusion. Previously, the addition of Kr (and other high-Z) dopants has been shown to enhance beam-target fusion yields at currents below 300 kA, with optimal concentrations at 1%–2% Kr, whereas here we show that the optimal concentration of Kr at the MA level is near 0.1% by volume—elucidating a trend in the optimal Kr doping concentration as a function of the device scale. The neutron time-of-flight data reveal that Kr doping creates shorter and more intense neutron bursts, likely due a tighter but unstable pinch, highlighting a key trade-off for Kr doping.

Gas puff Z-pinches are intense sources of X-rays and neutrons but are highly susceptible to the magneto-Rayleigh-Taylor instability (MRTI). MRTI mitigation is critical for optimal and reproducible yields, motivating significant attention toward various potential mitigation mechanisms. One such approach is the external application of an axial magnetic field, which will be discussed here in the context of recent experiments on the Zebra generator (1 MA, 100 ns) at the University of Nevada, Reno. In these experiments, an annular Kr gas liner is imploded onto an on-axis deuterium target with a pre-embedded axial magnetic field B z 0 ranging from 0 to 0.3 T. The effect of B z 0 on the stability of the Kr liner is evaluated with measurements of plasma radius, overall instability amplitude, and dominant instability wavelength at different times obtained from time-gated extreme ultraviolet pinhole images. It was observed that the external axial magnetic field does not affect the implosion velocity significantly and that it reduces the overall instability amplitude and the presence of short-wavelength modes, indicating improved pinch stability and reproducibility. For the highest applied B z 0 = 0.3 T, the stagnation radius measured via visible streak images was found to increase. These findings are consistent with experiments reported in the literature, but here, the B z 0 required for stability, B z 0 = 0.13 I p k / R 0 (where Ipk is the driver peak current and R0 is the initial radius), is lower. This could be attributed to the smaller load geometry, both radially and axially. Consistent with other experiments, the cause of decreased convergence cannot be explained by the additional axial magnetic pressure and remains an open question.

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.

In this paper we report on the ability of a compact current driver yielding 250 kA in 150 ns to produce counter-propagating plasma flows. The flows were produced by two vertically-opposed conical wire arrays separated by 1 cm, each comprised of 8 wires. With this array configuration, we were able to produce two supersonic plasma jets with velocities on the order of 100–200 km/s that propagate towards each other and collide. Aluminum wires were tested first; we observed a shock wave forming at the collision region that remained stationary for an extended period of time (∼50 ns) using optical probing diagnostics and Extreme Ultraviolet imaging. After this period, a bow shock is formed that propagates at 20 km/s towards the cathode of the array, likely due to small differences in the density and/or speed of the jets. The inter-jet ion mean free path was estimated to be larger than the shock scale length for aluminum, indicating that the shock is not mediated by collisions, but possibly by a magnetic field, whose potential sources are also discussed. Radiative cooling and density contrast between the jets were found to be important in the shock wave dynamics. We studied the importance of these effects by colliding jets of two different materials, using aluminum in one and copper in the other. In this configuration, the bow shock was observed to collapse into a thin shell and then to fragment, forming clumpy features. Simultaneously, the tip of the bow shock is seen to narrow as the bow shock moves at a similar speed observed in the Al–Al case. We discuss the similarity criteria for scaling astrophysical objects to the laboratory, finding that the dimensionless numbers are promising.

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.

Recent experiments on the 1 MA, 100 ns Zebra driver at the Nevada Terawatt Facility at the University of Nevada, Reno, investigated the compression of a deuterium target by a high-atomic-number (Ar or Kr) gas-puff liner. Pinch stability improved with axial premagnetization of 1–2 kG observed as a decrease in magneto-Rayleigh-Taylor instability growth. Implosion dynamics and stagnation conditions were studied computationally with the radiation-MHD code MACH2 using initial conditions that approximate those in the experiment. Typical average and peak implosion velocities exceeded 300 and 400 km/s, respectively, which raised the target adiabat by shock heating as the front converges on axis, at which time the target is adiabatically compressed to stagnation. Experimental fusion yields of up to 2 × 109 for Ar liner on D target implosions were measured, while with a Kr liner yields up to 1 × 1010 were measured. Higher yields in Kr compared to Ar were also calculated in 2-D MACH2 simulations. These observations will be further tested with other radiation-MHD codes, and experiments on the 1 MA LTD-III machine at UC San Diego.

A semi-analytic model is presented for the gas-puff Staged Z-pinch, a magneto-inertial fusion concept in which an annular gas-puff liner implodes onto a deuterium or deuterium-tritium target. The one-dimensional model is a modification of the semi-analytic model for MagLIF (SAMM) [R. D. McBride and S. A. Slutz, Phys. Plasmas 22, 052708 (2015)], that addresses the different set of physics inherent to a Staged Z-pinch implosion: azimuthal magnetic field transport, shock heating of the fuel, separate ion and electron energy equations, and a simplified radiation model that approximates the liner transition from optically thin to optically thick. Following the explanation of the model, three sample problems are presented: first, a Staged Z-pinch implosion on the Zebra driver (1 MA, 100 ns) is modeled and compared with the HYDRA simulation results; second, the MagLIF point design is modeled and compared to the original simulation results [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] and results from SAMM; and third, we conduct a simple parameter scan and scaling study for a Staged Z-pinch implosion on the LTD-III driver (0.8 MA, 160 ns). Some agreement with HYDRA and SAMM is obtained, and deuterium-deuterium (DD) neutron yield scaling with current is consistent with other existing models and HYDRA simulations.A semi-analytic model is presented for the gas-puff Staged Z-pinch, a magneto-inertial fusion concept in which an annular gas-puff liner implodes onto a deuterium or deuterium-tritium target. The one-dimensional model is a modification of the semi-analytic model for MagLIF (SAMM) [R. D. McBride and S. A. Slutz, Phys. Plasmas 22, 052708 (2015)], that addresses the different set of physics inherent to a Staged Z-pinch implosion: azimuthal magnetic field transport, shock heating of the fuel, separate ion and electron energy equations, and a simplified radiation model that approximates the liner transition from optically thin to optically thick. Following the explanation of the model, three sample problems are presented: first, a Staged Z-pinch implosion on the Zebra driver (1 MA, 100 ns) is modeled and compared with the HYDRA simulation results; second, the MagLIF point design is modeled and compared to the original simulation results [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] and results from SAM...

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 present the design of a gas-puff injector for liner-on-target experiments. The injector is composed of an annular high atomic number (e.g., Ar and Kr) gas and an on-axis plasma gun that delivers an ionized deuterium target. The annular supersonic nozzle injector has been studied using Computational Fluid Dynamics (CFD) simulations to produce a highly collimated (M > 5), ∼1 cm radius gas profile that satisfies the theoretical requirement for best performance on ∼1-MA current generators. The CFD simulations allowed us to study output density profiles as a function of the nozzle shape, gas pressure, and gas composition. We have performed line-integrated density measurements using a continuous wave (CW) He–Ne laser to characterize the liner gas density. The measurements agree well with the CFD values. We have used a simple snowplow model to study the plasma sheath acceleration in a coaxial plasma gun to help us properly design the target injector.

Target preheating is an integral component of magnetized inertial fusion in reducing convergence ratio. In the staged Z-pinch concept, it is achieved via one or more shocks. Previous work [Narkis et al., Phys. Plasmas 23, 122706 (2016)] found that shock formation in the target occurred earlier in higher-Z liners due to faster flux transport to the target/liner interface. However, a corresponding increase in magnitude of magnetic pressure was not observed, and target implosion velocity (and therefore shock strength) remained unchanged. To investigate other means of increasing the magnitude of transported flux, a Korteweg-de Vries-Burgers equation from the 1-D single-fluid, resistive magnetohydrodynamic equations is obtained. Solutions to the nondispersive (i.e., Burgers) equation depend on nondimensional coefficients, whose dependence on liner density, temperature, etc., suggests an increase in target implosion velocity, and therefore shock strength, can be obtained by tailoring the mass of a single-liner ...

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.

1- and 2-D simulations of 1-cm radius, gas-puff liners of Ne, Ar, Kr, and Xe imploding onto a deuterium target are conducted using the discharge parameters for the Zebra (1 MA, 130 ns) driver using the resistive MHD code MACH2. This is an implementation of the Staged Z-pinch concept, in which the target is driven to high-energy-density first by shock compression launched by a diffused azimuthal magnetic field ( J×B force), and then by the adiabatic compression as the liner converges on axis. During the run-in phase, the initial shock heating preheats the deuterium plasma, with a subsequent stable, adiabatic compression heating the target to high energy density. Shock compression of the target coincides with the development of a J×B force at the target/liner interface. Stronger B-field transport and earlier shock compression increases with higher-Z liners, which results in an earlier shock arrival on axis. Delayed shock formation in lower-Z liners yields a relative increase in shock heating, however, the 2...