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The goal of the Xflows experimental campaign is to study the radiation flow on the National Ignition Facility (NIF) reproducing the sensitivity of the temperature (±8 eV, ±23 μm) and density (±11 mg/cc) measurements of the COAX platform [Johns et al., High Energy Density Phys. 39, 100939 (2021); Fryer et al., High Energy Density Phys. 35, 100738 (2020); and Coffing et al., Phys. Plasmas 29, 083302 (2022)]. This new platform will enable future astrophysical experiments involving supernova shock breakout, such as Radishock (Johns et al., Laboratory for Laser Energetics Annual Report 338, 2020) on OMEGA-60 [Boehly et al., Rev. Sci. Instrum. 66, 508 (1995)], and stochastic media (such as XFOL on OMEGA). Greater energy and larger physical scale on NIF [Moses et al., Eur. Phys. J. D 44, 215 (2007)] will enable a greater travel distance of radiation flow, higher density, and more manufacturable foams and enable exploration of a greater range of radiation behavior than achievable in the prior OMEGA experiments. This publication will describe the baseline configuration for the Xflows experimental campaign and the roadmap to achieve its primary objectives.

In this paper, we report on a crystal based x-ray imaging system fielded at the OMEGA EP laser facility. This new system has a pointing accuracy of +/100 μm, a temporal resolution down to 100 ps (depending on backlighter characteristics), variable magnification, and a spatial resolution of 21.9 µm at the object plane at a magnification of 15×. The system is designed to use a crystal along the crystal plane that satisfies the Bragg condition for the x ray of interest. The thin crystal is then bent into a spherical geometry and attached to a glass backing substrate to hold it in the diagnostic, and the x rays are imaged onto a charge coupled device. We report on data acquired with the new Los Alamos National Laboratory supplied spherical quartz crystal to image the Mn He-α 6.15 keV line emission.

We examine the effects of varying the magnitude of an applied, uniform, axial magnetic field ( $B_{z}$ ) on the formation of laboratory plasma jets produced by a 1-MA 100-ns rise time pulsed power generator in a radial foil configuration. A Helmholtz coil applies the external magnetic field (0 to 2 T). With a small-enough applied field, the foil surface ablation is relatively azimuthally uniform, and $J\times B$ forces drive the ablated plasma inward and upward to form a well-defined azimuthally symmetric jet. Using applied field strengths larger than a critical $B_{z} = 1.1\pm 0.1$ T with aluminum foils, the plasma ablation is not azimuthally uniform, discrete bursts of plasma initiate from the foil surface, and the formation of a well-defined jet is disrupted. The critical $B_{z}$ for this plasma jet formation disruption correlates with the foil material’s electrical resistivity and equation of state (EOS). To better understand the material-dependent phenomenon, we compare the experimental results with 3-D extended magnetohydrodynamics simulations of ablation of a 2 mm $\times 2$ mm by 25- $\mu \text{m}$ slab that represents a section of the radial foil. The simulations initialize the slab in the solid state and include the material resistivity and EOS from the solid to plasma phases. As is observed in the experimental disruption, these simulations show enhanced nonuniform plasma ablation with an applied $B_{z}$ , which can inhibit the azimuthal uniformity necessary to produce a well-defined plasma jet. Furthermore, the simulations also show a material and resistivity dependence on the ablation process similar to the trend shown by the experiments. These results demonstrate the necessity of accurate, detailed modeling of material properties during the transition from solid to plasma phases.

We present experimental data providing evidence for the formation of transient ( ${\sim }20\ \mathrm {\mu }\textrm {s}$ ) plasmas that are simultaneously weakly magnetized (i.e. Hall magnetization parameter $\omega \tau > 1$ ) and dominated by thermal pressure (i.e. ratio of thermal-to-magnetic pressure $\beta > 1$ ). Particle collisional mean free paths are an appreciable fraction of the overall system size. These plasmas are formed via the head-on merging of two plasmas launched by magnetized coaxial guns. The ratio $\lambda _{\textrm {gun}}=\mu _0 I_{\textrm {gun}}/\psi _{\textrm {gun}}$ of gun current $I_{\textrm {gun}}$ to applied magnetic flux $\psi _{\textrm {gun}}$ is an experimental knob for exploring the parameter space of $\beta$ and $\omega \tau$ . These experiments were conducted on the Big Red Ball at the Wisconsin Plasma Physics Laboratory. The transient formation of such plasmas can potentially open up new regimes for the laboratory study of weakly collisional, magnetized, high- $\beta$ plasma physics; processes relevant to astrophysical objects and phenomena; and novel magnetized plasma targets for magneto-inertial fusion.

We numerically model the ablation process of a 25- $\mu \text{m}$ -thick aluminum foil driven by a pulsed-power machine that provides a 1-MA peak current in a 100-ns zero-to-peak rise time. The extended magnetohydrodynamics simulation is a discontinuous Galerkin code with Cartesian coordinates in 3-D and with 25- $\mu \text{m}$ spatial resolution. We investigate the influence of an external magnetic field normal to the foil surface, $B_{z}$ . During the foil ablation, $B_{z}=1$ T causes more nonuniform distributions of density and current compared to $B_{z}=0$ T. $B_{z}=4$ T delays the generation of surface plasma relative to the 0- and 1-T cases. The understanding of a material’s ablation as it undergoes transition from the solid to plasma phases requires detailed knowledge of a material’s equation of state and conductivity. This paper of warm dense matter and how instabilities propagate from a solid material to plasma motivates improvements to both numerical simulations and experimental diagnostics.

Ar gas puff z-pinch experiments were conducted on the 0.9-MA, 200-ns COBRA generator at Cornell University. In the experiments, a triple-nozzle gas valve was used to produce the z-pinch load with concentric outer and inner gas puffs and a central gas jet. We used a planer laser-induced fluorescence to measure the initial gas profile of the load, two four-frame 4-ns gated extreme ultraviolet cameras to image the imploding plasma, and filtered photoconducting diamond detectors to measure the X-ray output. We have observed the shock heating and/or photoionization of the dense center jet by the imploding plasma. With an outer-to-inner plenum pressure ratio of 1:3, deacceleration of the imploding plasma occurred when the outer plasma shell imploded on the inner shell resulting in a stable implosion. By varying the plenum pressure for the center jet, the X-ray emission was optimized. An Ar K-shell X-ray (3–4 keV) yield of 77 ± 17 J was produced at a current level of 0.87 ± 0.2 MA and an implosion time of 200 ns.

Thomson scattering measurements were performed on plasma jets created from a 15- $\mu \text{m}$ -thick radial Al foil load on a 1-MA pulsed power machine. The laser used for these measurements has a maximum energy of 10 J at 526.5 nm. Using the full energy, however, significantly heats the $5\times 10^{18}$ cm−3 jet by inverse bremsstrahlung, creating a density bubble in the jet. To measure the evolving plasma parameters of this laser-heated jet, a streak camera was used to record the scattered spectrum, resulting in the sub-ns time-resolved Thomson scattering. Analysis of the streak camera image showed that the electron temperature of the jet was about 25 eV prior to the laser pulse. The laser then heated the plasma to 80–100 eV within about 2 ns. The electron temperature then stabilized for about 0.5 ns prior to falling at the end of the laser pulse. Jets made from a radial Ti foil showed more heating by the laser than the Al jets, going from 50 to over 150 eV, and heating was detected even when only 1 J of laser energy was used. Also, the ion-acoustic peaks in the scattered spectrum from the Ti jets were significantly narrower than those from Al jets, a result of several possible differences in the plasma created from these two materials.

Recent work reported on the current density in pulsed-power-driven liners where a vacuum gap was introduced in the power feed connecting the liner to the generator. The resultant gap flashover generates azimuthally localized current-carrying plasma channels, which can create an azimuthal nonuniformity in the current density. The current density evolves during the current pulse, but nonuniformity is observed through the experiment timescale. Magnetohydrodynamic simulation work in 3-D demonstrates the difficulty in reproducing the experimental data within a limited computational domain, and those boundary conditions may dominate this paper. The development of current-driven instabilities in the plasma channels can explain the liner current density evolution, and specifically the ion acoustic instability can account for the main features observed in the experiments.

In this paper, collimated plasma jets form from Joule heating and ablation of a radial foil (Al 15- $\mu \text{m}$ -thin disk) using a pulsed power generator (Cornell Beam Research Accelerator) with 1-MA peak current and 100-ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform external magnetic field ( $\sim 1$ -T axial $B_{z}$ produced from a pulsed Helmholtz coil) and under a change of current polarity, which corresponds to current moving either radially inward or outward from the foil’s central axis. Experimental results are compared with predictions made by numerical simulations (Plasma as an Extended-MHD Relaxation System using an Efficient Upwind Scheme). The influence of the Hall effect on the jet development is observed under opposite current polarities.

In this paper, we introduce a novel experimental platform for the study of the Richtmyer–Meshkov instability in a cylindrically converging geometry using a magnetically driven cylindrical piston. Magnetically driven solid liner implosions are used to launch a shock into a liquid deuterium working fluid and, ultimately, into an on-axis rod with a pre-imposed perturbation. The shock front trajectory is tracked through the working fluid and up to the point of impacting the rod through the use of on axis photonic Doppler velocimetry. This configuration allows for precise characterization of the shock state as it impacts the perturbed rod interface. Monochromatic x-ray radiography is used to measure the post-shock interface evolution and rod density profile. The ALEGRA MHD model is used to simulate the dynamics of the experiment in one dimension. We show that late in time the perturbation growth becomes non-linear as evidenced by the observation of high-order harmonics, up to n = 5. Two dimensional simulations performed using a combination of the GORGON MHD code and the xRAGE radiation hydrodynamics code suggest that the late time non-linear growth is modified by convergence effects as the bubbles and spikes experience differences in the pressure of the background flow.

We observe shock-front separation and species-dependent shock widths in multi-ion-species collisional plasma shocks, which are produced by obliquely merging plasma jets of a He/Ar mixture (97% He and 3% Ar by initial number density) on the Plasma Liner Experiment [S. C. Hsu et al., IEEE Trans. Plasma Sci. 46, 1951 (2018)]. Visible plasma emission near the He-I 587.6 nm and Ar-II 476.5-514.5 nm lines are simultaneously recorded by splitting a single visible image of the shock into two different fast-framing cameras with different narrow bandpass filters (589 +/- 5 nm for observing the He-I line and 500 +/- 25 nm for the Ar-II lines). For conditions in these experiments (pre-shock ion and electron densities ~5*10^14 cm^-3, ion and electron temperatures of ~2.2 eV, and relative plasma-merging speed of 22 km/s), the observationally inferred magnitude of He/Ar shock-front separation and the shock widths themselves are < 1 cm, which correspond to ~50 post-shock thermal ion-ion mean free paths. These experimental lengths scales are in reasonable qualitative and quantitative agreement with results from 1D multi-fluid simulations using the Chicago code. However, there are differences between the experimentally-inferred and simulation-predicted ionization states and line emission intensities, particularly in the post-shock region. Overall, the experimental and simulation results are consistent with theoretical predictions that the lighter He ions diffuse farther ahead within the overall shock front than the heavier Ar ions.

We have conducted Ar gas puff z-pinch studies on the COBRA generator with an external Bz field. Two ~20 cm diameter coils are used to generate up to 6 kG Bz field on the pinch axis. A triple-nozzle injects two concentric annular gas puffs and a center jet into the load region. The z-pinch implosion starts from the outer puff at~3 cm in radius, slows down by the inner puff at the radius of ~ 1.5 cm, and then imploded on the center jet (R~0.5 cm). The de-acceleration of implosion by the inner puff reduces the grows of the magneto-Rayleigh-Taylor (MRT) instability. Stable implosions and ~200 J Ar K-shell yields are achieved with the outer, inner, and jet nozzle plenum pressure at 0.8, 2.4, and ~10 psia, respectively. In the absence of the inner gas puff, the implosion starts from 3 cm in radius accelerates to the center jet. The MRT instability grows rapidly and the implosion is not stable as observed. Subtitling the inner puff with an applied the external Bz field, the compression of the Bz field trapped between the outer and jet plasma slows down the implosion, and the MRT instability is suppressed. We have observed not only the stabilization of the implosion, but also the heating of the center jet plasma by the compression of the trapped magnetic field, and the helix -like structures in the imploding plasma.

In the present research, plasma jets form from Joule heating and ablation of a radial foil (approximately 15 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. We study the effects on jet dynamics resulting from varying an applied uniform axial magnetic field (Bz) from 0 to 2 T. We empirically observe a disruption of the plasma jet collimation, for which plasma is ej ected from the foil as discrete bursts and does not form an azimuthally symmetric plasma jet. The critical Bz for the disruption depends upon the foil material (Al, Ti, Ni, Cu, Zn, Mo, W). The disruption initiates from the foil surface and is dependent upon material properties such as electrical conductivity and equation of state. The applied Bz acts with the higher conductivity materials to facilitate nonuniform plasma and current filamentation that breaks the azimuthal symmetry needed to form the plasma jet. The plasma filamentation likely originates from initial perturbations (in density and resistivity) in the higher-density solid-liquid phases. 3D numerical simulations in Cartesian coordinates (using the extended magnetohydrodynamics code, PERSEUS) of a section of the ablating foil reproduce some of the experimental trends including the external magnetic field dependence and material resistivity dependence of the generation of plasma and current nonuniformities.

Streaked Thomson scattering measurements have been performed on plasma jets created from a 15 $\mu\mathrm{m}$ thick radial Al, Ti, or Cu foil load on COBRA, a 1 MA pulsed power machine. The streaked system enables collecting scattered light from two separate laser pulses separated in time by between 3 and 14 ns from two different scattering angles. The time separation is created by splitting the initial 2.2 ns full width half max duration, 10 J, 526.5 nm laser beam into two separate pulses, each with 2.5 J, and delaying one beam relative to the other. To collect streaked spectra from two angles simultaneously a split fiber bundle was used to couple light from the plasma to the spectrometer, and the size of the fibers, 100 $\mu \mathrm{m}$ diameter, was used as the effective spectral slit width. The 2.5 J laser pulse is shown to heat the plasma jet by inverse bremsstrahlung radiation, as measured by the streaked Thomson scattering system. Analysis of the streak camera image showed that the electron temperature of the Al jet was increased from 20 eV up to 50 eV within about 2 ns for both laser pulses when they were separated by 12 ns in time. Initial results from the Cu jets showed more heating then the Al jets while Ti jets showed the most heating of these three materials. In addition to this increased heating, the scattering profiles from Ti and Cu jets had ion-acoustic features that were more difficult to interpret then those from Al jets. Results from the two scattering angles showed reasonable agreement of the measured electron temperature, and implied that the electron density was at least $2\times 10^{18}\text{cm}^{-3}$ . Results will also be presented with the laser pulses separated by only 4 ns, creating a more continuous laser pulse. In addition, the effects of the current polarity in the radial foil on the measured electron temperature will be shown.

Thomson scattering measurements have been performed on laboratory plasma jets in order to measure the flow velocities and electron temperatures inside and near the edge of the jet. These jets were created using $\mathrm {a}15 \mu \mathrm {m}$ thick radial Al foil load on COBRA, a 1 MA pulsed power machine. The laser used for these measurements had a maximum energy of 10 J at 526.5 nm. Using this 10 J laser, however, significantly heats the $5\mathrm {x} 10 ^{18}$ cm $^{-3}$ jet by inverse bremsstrahlung, creating a density bubble in the jet. This was demonstrated by reducing the probe laser energy to 1 J, which reduced the measured electron temperature in the jet from about 40 to 20 eV and nearly eliminated the bubble. These measurements were made using a time gated spectrometer, with at least a 5 ns gate window, in order to encompass the entire 3 ns laser pulse. Therefore, no time dependent electron temperature measurements could be made from the Thomson scattering spectra. We are now developing an experimental arrangement to send the collected scattered spectra into a streak camera, in order to determine the plasma temperature as a function of time throughout the 3 ns laser pulse. With the streak camera data, we hope to track the changing plasma parameters during the laser heating of the plasma jet. In the future we hope to extend this diagnostic arrangement to other configurations, enabling time resolved measurements of the plasma parameters of various plasmas.

In the present research, plasma jets form from Joule heating and ablation of a radial foil (approximately 15 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. We study the effects on jet dynamics resulting from varying an applied uniform axial magnetic field (Bz) from 0 to 2 T. We empirically observe a disruption of the plasma jet collimation. The critical Bz for the disruption depends upon the foil material (Al, Ti, Ni, Cu, Zn, Mo, W). The disruption initiates from the foil surface and is dependent upon material mass as well as the solid electrical or thermal resistivities. We consider how the different foil materials affect the plasma magnetization, radiative losses, and formation time of surface plasma. The axial magnetic field larger than the critical Bz can break the azimuthal symmetry of the foil ablation.

On the 20 MA Z machine, the helical instability features that are observed in magnetized metal liner experiments were mitigated using a dielectric coating. 1In the experiments to be presented, we compare results using liners with and without a dielectric coating and without an applied axial magnetic field on the 1 MA, 100-200 ns COBRA pulsed power generator at Cornell University. 2Diagnostics used in these experiments include 4-frame extreme ultraviolet imaging, 3-frame laser imaging, and high resolution X-ray radiography. This combination of diagnostics enables investigation of plasma formation and evolution ranging from the higher density $( > 10 ^{19} /$cm $^{3})$region close to the initial liner radius to the lower density regions $\sim 0.3$mm from that radius.

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.

We have conducted Ar gas puff z-pinch studies on the COBRA generator. A triple-nozzle is used to produce tailored gas density distributions with two concentric annular nozzles and a center gas jet. We report suppression of Rayleigh-Taylor instabilities by inner dense plasmas, and photo-ionization of the inner gas puffs by the hot outer imploding plasma. By varying the initial gas density profiles, we have optimized the Ar K-shell x-ray radiation, and produced stable 200-ns implosions.

We present a method to seamlessly self-assemble, disassemble, transport, and reconstruct ordered 2-D structures of fluid-borne microspheres on a surface using an array of magnetic zigzag wire traps. Competition between and control over: 1) the trapping forces of underlying magnetic patterns; 2) magnetic dipole repulsion; and 3) Brownian motion gives rise to reproducible cluster structures. Weak external magnetic fields $({ tune the spacing between particles and enable the assembled structures to be remotely manipulated and reassembled on the platform. This method could be used in biological and photonic applications by utilizing the microspheres, for example, as carriers of host biomolecules or as linkers to fluorescent emitters.

A platform of microscopic magnetic wires and discrete bits of disks patterned on a surface offers dynamic control over the motion of fluid borne magnetic particles. The energy landscape associated with the local domain wall field originating from zigzag wire vertices is tuned by weak external fields to vary Brownian trajectories between strong confinements and delocalized spatial excursions. The corresponding spatial coverage of single particle trajectories allows the energy profile of such a magnetic trap to be mapped. Remote manipulation and guided transport of these objects across various opaque and transparent rigid surfaces as well as flexible films supporting discrete magnetic disks is presented.

We present a study investigating the distribution of current density in solid, metallic liners directly relevant to the MagLIF approach to fusion. Here, the liner thickness is large compared to the collisionless skin depth, and a vacuum gap is introduced in the power feed to simulate the load method on the Z machine at Sandia Laboratories. We present optical emission data along with a 3D magnetic field mapping method from aluminum liner loads on the 1 MA, 100ns COBRA generator.

In the present research, plasma jets form from Joule heating and ablation of a radial foil (∼15 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. We study the effects on jet dynamics resulting from varying an applied uniform axial magnetic field (Bz) from 0 to 1.8 T. We empirically observe a disruption of the plasma jet collimation. The critical Bz for the disruption depends upon the foil material (Al, Ti, Ni, Cu). We discuss physical reasons for the material dependence of the disruption.

The dynamics of Magnetized Liner Inertial Fusion (MagLIF)1, a new and promising approach to pulsed power fusion, are presently under detailed study at Sandia National Laboratories. Alongside this, a comprehensive analysis of the influence of the specific liner design geometry in the MagLIF system on liner initiation is underway in the academic community.

A single channel sub-nanosecond time-resolved Thomson scattering system used for pulsed power-driven high energy density plasma measurements has been upgraded to give electron temperatures at two different times and from two different angles simultaneously. This system was used to study plasma jets created from a 15 μm thick radial Al foil load on a 1 MA pulsed power machine. Two laser pulses were generated by splitting the initial 2.3 ns duration, 10 J, 526.5 nm laser beam into two pulses, each with 2.5 J, and delaying one relative to the other by between 3 and 14 ns. Time resolution within each pulse was obtained using a streak camera to record the scattered spectra from the two beams from two scattering angles. Analysis of the scattering profile showed that the electron temperature of the Al jet increased from 20 eV up to as much as 45 eV within about 2 ns by inverse bremsstrahlung for both laser pulses. The Thomson scattering results from jets formed with opposite current polarities showed different laser heating of the electrons, as well as possibly different ion temperatures. The two-angle scattering determined that the electron density of the plasma jet was at least 2 × 1018 cm-3.

As part of the work on the Magnetized Liner Inertial Fusion (MagLIF) concept1, Awe et al. found on the 20 MA Z-machine that applying an externally generated axial magnetic field to a liner produces a helical striation pattern in the liner2. We are investigating this phenomenon using 10 mm long cylindrical metal liners having 4 mm diameter and varying wall thickness on the 1 MA, 100–230 ns COBRA pulsed power generator at Cornell University. In addition, we will present experimental results on a configuration that includes a wire initially connecting the cathode and anode on the axis of a cylindrical liner that does not initially connect the cathode to the anode. Results of these experiments both with and without external magnetic fields will be shown. Extreme ultraviolet (XUV) imaging as well as optical streak and 12 frame camera imaging are used to observe and analyze liner surface emission. Axial and side-on interferometry are used to determine the distribution of plasma both near the liner surface and inside the liner, assessing, among other things, the impact of non-uniformities during the plasma ablation phase of the experiments.

Radiative losses are known to play an important role in the development of hydrodynamic instabilities in many astrophysical (Core-collapse supernovae; HH objects) and laboratory (Inertial confinement fusion) environments. The fielding of triple-annular gas-puff valves on university level pulsed-power generators [1][2] enables study of these instabilities in carefully controlled environments, for inviscid Re >> 1, non-diffusive Pe >> 1 fluids, where radiative losses on dynamically-relevant timescales can be significant. Furthermore, the acceleration of the unstable boundary and radiative cooling rates can both be specified, by variation of nozzle backing-pressures and gas species respectively.

In the present research, collimated plasma jets form from Joule heating and ablation of a radial foil (Al 20 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform external magnetic field (∼1 T axial Bz) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foil's central axis. Experimental results are compared with predictions made by numerical simulations (PERSEUS)1. The influence of the Hall effect on the jet development is observed under opposite current polarities. Before jet formation, initial plasma on top of the foil surface develops discrete narrow current path channels (tendrils) that display characteristics of electrothermal-filamentation plasma instability. A disruption of the tendrils and subsequent jet is noticed after a modest increase in the applied field strength from 1 to 1.5 T, which is not predicted by the 2D (r-z) simulations.

We experimentally measure the effects of an applied axial magnetic field (Bz) on laboratory plasma jets and compare the experimental results with numerical simulations using an extended magnetohydrodynamics code. A 1 MA peak current, 100 ns rise time pulse power machine is used to generate the plasma jet. On application of the axial field, we observe on-axis density hollowing and a conical formation of the jet using interferometry, compression of the applied Bz using magnetic B-dot probes, and azimuthal rotation of the jet using Thomson scattering. Experimentally, we find densities ≲5 × 1017 cm−3 on-axis relative to jet densities of ≳3 × 1018 cm−3. For aluminum jets, 6.5 ± 0.5 mm above the foil, we find on-axis compression of the applied 1.0 ± 0.1 T Bz to a total 2.4 ± 0.3 T, while simulations predict a peak compression to a total 3.4 T at the same location. On the aluminum jet boundary, we find ion azimuthal rotation velocities of 15–20 km/s, while simulations predict 14 km/s at the density peak. We discuss possible sources of discrepancy between the experiments and simulations, including surface plasma on B-dot probes, optical fiber spatial resolution, simulation density floors, and 2D vs. 3D simulation effects. This quantitative comparison between experiments and numerical simulations helps elucidate the underlying physics that determines the plasma dynamics of magnetized plasma jets.

Tests of the magnetized liner inertial fusion (MagLIF) concept will make use of the 27 MA Z-machine at Sandia National Laboratories, Albuquerque, to implode a cylindrical metal liner to compress and heat a preheated plasma contained within it [1]. While most pulsed power machines produce much lower currents than the Z-machine, there are questions that can still be answered on smaller scale setups. Recent work on the Cornell Beam Research Accelerator (COBRA) has made use of cylindrical metal liners made in-house to study the initiation of plasma on the liner surface and axial magnetic field compression. Although such liners are not sufficiently uniform for MagLIF-relevant studies of liner dynamics during implosion, they can make early-time studies of cylindrical liner implosions viable for smaller laboratories. This paper will present experimental results of imploding liners having imperfect uniformity to assess the impact that has on initiation and ablation. Extreme ultraviolet (XUV) imaging as well as optical streak imaging is used to assess when and where non-uniform-driven emission occurs. Axial interferometry is used to determine the distribution of plasma near the liner surface, including the impact of non-uniformities during the plasma initiation and ablation phases of the experiments.

Radial foil implosions on pulsed-power generators [1] can produce strongly collimated plasma jets. The typical ratio of the jet length to its radius is at least 20. These jets have large Reynolds and magnetic Reynolds numbers. Due to favorable scaling [2], they can be considered as a reasonable embodiment of collimated astrophysical plasma jets generated by protostars, planetary nebula or galactic nuclei. However, many of these astrophysical jets seem to strongly diverge near their base while flow collimation occurs much later downstream (e.g. M2-9). Using a set of twisted pins to add a strong axial magnetic field (≫ 10 T) at the base of a jet produced by radial foils, we show that conical plasma jet can be formed consistently and repeatedly on COBRA. While these jets arc strongly divergent at their base, the jet collimates rapidly as the axial magnetic field weakens. Using the 3D PERSEUS code [3], we show that the conical part of the jet is formed by the imposed axial field and the top part of jet, while extremely hollow, is collimated by the same mechanisms ruling non-magnetized plasma jets [4]. Code results are scaled to lengths similar to planetary nebula size and show how scaling affects the plasma dynamics of strongly magnetized plasma jets.

Tests of the magnetized liner inertial fusion (MagLIF) concept will make use of the 27 MA Z machine at Sandia National Laboratories, Albuquerque, to implode a cylindrical metal liner to compress and heat preheated, magnetized plasma contained within it. While most pulsed power machines produce much lower currents than the Z-machine, there are issues that can still be addressed on smaller scale facilities. Recent work on the Cornell Beam Research Accelerator (COBRA) has made use of 10 mm long and 4 mm diameter metal liners having different wall thicknesses to study the initiation of plasma on the liner’s surface as well as axial magnetic field compression [P.-A. Gourdain et al., Nucl. Fusion 53, 083006 (2013)]. This report presents experimental results with non-imploding liners, investigating the impact the liner’s surface structure has on initiation and ablation. Extreme ultraviolet (XUV) imaging and optical 12 frame camera imaging were used to observe and assess emission non-uniformities as they developed. Axial and side-on interferometry was used to determine the distribution of plasma near the liner surface, including the impact of non-uniformities during the plasma initiation and ablation phases of the experiments.

In the present research, collimated plasma jets form from ablation of a radial foil (Al 20 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform axial magnetic field (1 T) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foil's central axis. Experimental results are compared with numerical simulations (PERSEUS). The influence of the Hall effect on the jet development is observed under opposite current polarities. Additionally, the magnetic field compression within the jet is examined. Further studies will compare the laboratory-generated plasma jets and astrophysical jets with embedded magnetic fields.

The demand for high-throughput single cell assays is gaining importance because of the heterogeneity of many cell suspensions, even after significant initial sorting. These suspensions may display cell-to-cell variability at the gene expression level that could impact single cell functional genomics, cancer, stem-cell research and drug screening. The on-chip monitoring of individual cells in an isolated environment would prevent cross-contamination, provide high recovery yield, and enable study of biological traits at a single cell level. These advantages of on-chip biological experiments is a significant improvement for myriad of cell analyses over conventional methods, which require bulk samples providing only averaged information on cell metabolism. We report on a device that integrates mobile magnetic trap array with microfluidic technology to provide, combined functionality of separation of immunomagnetically labeled cells or magnetic beads and their encapsulation with reagents into pico-liter droplets. This scheme of simultaneous reagent delivery and compartmentalization of the cells immediately after sorting, all performed seamlessly within the same chip, offers unique advantages such as the ability to capture cell traits as originated from its native environment, reduced chance of contamination, minimal use and freshness of the reagent solution that reacts only with separated objects, and tunable encapsulation characteristics independent of the input flow. In addition to the demonstrated preliminary cell viability assay, the device can potentially be integrated with other up- or downstream on-chip modules to become a powerful single-cell analysis tool.

We present a study of the time varying current density distribution in solid metallic liner experiments at the 1 MA level. Measurements are taken using an array of magnetic field probes which provide 2D triangulation of the average centroid of the drive current in the load at 3 discrete axial positions. These data are correlated with gated optical self-emission imaging which directly images the breakdown and plasma formation region. Results show that the current density is azimuthally non-uniform and changes significantly throughout the 100 ns experimental timescale. Magnetic field probes show clearly motion of the current density around the liner azimuth over 10 ns timescales. If breakdown is initiated at one azimuthal location, the current density remains non-uniform even over large spatial extents throughout the current drive. The evolution timescales are suggestive of a resistive diffusion process or uneven current distributions among simultaneously formed but discrete plasma conduction paths.

Awe et al. found on the 20 MA Z machine [Acta Phys. Pol. A 115, 956 (2009)] that applying an externally generated axial magnetic field to an imploding liner leads to a helical pattern in the liner when viewed with soft x-ray radiography ([Phys. Rev. Lett. 111, 235005 (2013)] and [Phys. Plasmas 21, 056303 (2014)]). Here, we show that this phenomenon is also observed in extreme ultraviolet self-emission images of 10 mm long cylindrical metal liners having varying diameters and varying wall thicknesses on a 1 MA, 100–200 ns pulsed power generator. The magnetic field in these experiments is created using either twisted return current wires positioned close to the liner, generating a time-varying Bz, or a Helmholtz coil, generating a steady-state Bz.

We present an experimental study of plasma initiation of a solid metal liner at the 1 MA level. In contrast to previous work, we introduce a vacuum gap at one of the liner connections to the power feed to investigate how this affects plasma initiation and to infer how this may affect the symmetry of the liner in compression experiments. We observed that the vacuum gap causes non-uniform plasma initiation both azimuthally and axially in liners, diagnosed by gated optical imaging. Using magnetic field probes external to the liner, we also determined that the optical emission is strongly linked to the current distribution in the liner. The apparent persistent of azimuthal non-uniformities may have implications for fusion-scale liner experiments.

We describe a technique by which magnetic field probes are used to triangulate the exact position of breakdown in a high voltage coaxial vacuum gap. An array of three probes is placed near the plane of the gap with each probe at 90° intervals around the outer (anode) electrode. These probes measure the azimuthal component of the magnetic field and are all at the same radial distance from the cylindrical axis. Using the peak magnetic field values measured by each probe, the current carried by the breakdown channel, and Ampères law we can calculate the distance away from each probe that the breakdown occurred. These calculated distances are then used to draw three circles each centered at the centers of the corresponding magnetic probes. The common intersection of these three circles then gives the predicted azimuthal location of the center of the breakdown channel. Test results first gathered on the coaxial gap breakdown device (240 A, 25 kV, 150 ns) at the University of California San Diego and then on COBRA (1 MA, 1 MV, 100 ns) at Cornell University indicate that this technique is relatively accurate and scales between these two devices.