A series of experiments has been conducted in order to investigate the azimuthal structures formed by the interactions of cylindrically converging plasma flows during the ablation phase of aluminium wire array Z pinch implosions. These experiments were carried out using the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. The main diagnostic used in this study was a two-colour, end-on, Mach-Zehnder imaging interferometer, sensitive to the axially integrated electron density of the plasma. The data collected in these experiments reveal the strongly collisional dynamics of the aluminium ablation streams. The structure of the flows is dominated by a dense network of oblique shock fronts, formed by supersonic collisions between adjacent ablation streams. An estimate for the range of the flow Mach number (M ¼ 6.2-9.2) has been made based on an analysis of the observed shock geometry. Combining this measurement with previously published Thomson Scattering measurements of the plasma flow velocity by Harvey-Thompson et al. [Physics of Plasmas 19, 056303 (2012)] allowed us to place limits on the range of the ZT e of the plasma. The detailed and quantitative nature of the dataset lends itself well as a source for model validation and code verification exercises, as the exact shock geometry is sensitive to many of the plasma parameters. Comparison of electron density data produced through numerical modelling with the Gorgon 3D MHD code demonstrates that the code is able to reproduce the collisional dynamics observed in aluminium arrays reasonably well. V C 2013 American Institute of Physics. [http://dx

Three-dimensional extended-magnetohydrodynamic simulations of the stagnation phase of inertial confinement fusion implosion experiments at the National Ignition Facility are presented, showing selfgenerated magnetic fields over 10 4 T. Angular high mode-number perturbations develop large magnetic fields, but are localized to the cold, dense hot-spot surface, which is hard to magnetize. When low-mode perturbations are also present, the magnetic fields are injected into the hot core, reaching significant magnetizations, with peak local thermal conductivity reductions greater than 90%. However, Righi-Leduc heat transport effectively cools the hot spot and lowers the neutron spectra-inferred ion temperatures compared to the unmagnetized case. The Nernst effect qualitatively changes the results by demagnetizing the hot-spot core, while increasing magnetizations at the edge and near regions of large heat loss.

We present a detailed study of magnetic reconnection in a quasi-two-dimensional pulsed-power driven laboratory experiment. Oppositely directed magnetic fields (B ¼ 3 T), advected by supersonic, subAlfvénic carbon plasma flows (V in ¼ 50 km=s), are brought together and mutually annihilate inside a thin current layer (δ ¼ 0.6 mm). Temporally and spatially resolved optical diagnostics, including interferometry, Faraday rotation imaging, and Thomson scattering, allow us to determine the structure and dynamics of this layer, the nature of the inflows and outflows, and the detailed energy partition during the reconnection process. We measure high electron and ion temperatures (T e ¼ 100 eV, T i ¼ 600 eV), far in excess of what can be attributed to classical (Spitzer) resistive and viscous dissipation. We observe the repeated formation and ejection of plasmoids, consistent with the predictions from semicollisional plasmoid theory. DOI: 10.1103/PhysRevLett.118.085001 Magnetic reconnection is the rapid change of magnetic field topology in a plasma, accompanied by bulk heating and particle acceleration [1,2]. Reconnection is a ubiquitous process that occurs across a vast region of parameter space, including the collisionless plasmas at the heliopause [3] and the dense, hot plasmas deep in the solar convection zone [4,5]. Our understanding of magnetic reconnection has improved over the years thanks to dedicated laboratory experiments. In facilities like MRX [6][7][8] and TREX [9] the magnetic energy is much larger than the other plasma energy components. In contrast, laser-driven high energy density experiments are strongly driven-the kinetic and thermal energies are much larger than the magnetic energy [10,11], and reconnection heating is small [12].In this Letter we present experimental studies of high energy density magnetic reconnection driven by a new pulsed-power platform. The reconnection layer was created by the interaction of magnetized plasma flows in a quasi-2D geometry, which we studied using high resolution, nonperturbative measurements of the temperature, flow velocity, electron density, and magnetic field in the reconnection layer. The colliding plasma flows were supersonic (M s ∼ 1.6) but sub-Alfvénic (M A ∼ 0.7), and therefore the thermal and dynamic plasma betas (ratio of the thermal or ram pressure to the magnetic pressure) are close to unity (β th ∼ 0.7, β dyn ∼ 0.9). These parameters are significantly different from those found both in magnetically driven experiments, such as MRX, and in laser driven experiments, and we believe our experiments are the first to make a detailed study of this regime. We observed the formation of a reconnection layer with an aspect ratio of L=δ > 10, which existed for at least ten hydrodynamic flow times δ=V in , where L is the layer half length and δ is the layer half width [ Fig. 1(a)]. The annihilation of the magnetic flux caused strong plasma heating in the reconnection layer (T i ≈ 600 eV,ZT e ≈ 600 with T e ≈ 100 eV in a carbon plasma with average ionizationZ ≈ 6)...

We describe magnetic reconnection experiments using a new, pulsed-power driven experimental platform in which the inflows are super-sonic but sub-Alfvénic. The intrinsically magnetised plasma flows are long lasting, producing a well-defined reconnection layer that persists over many hydrodynamic time scales. The layer is diagnosed using a suite of high resolution laser based diagnostics which provide measurements of the electron density, reconnecting magnetic field, inflow and outflow velocities and the electron and ion temperatures. Using these measurements we observe a balance between the power flow into and out of the layer, and we find that the heating rates for the electrons and ions are significantly in excess of the classical predictions. The formation of plasmoids is observed in laser interferometry and optical self-emission, and the magnetic O-point structure of these plasmoids is confirmed using magnetic probes.

A new experimental platform was developed, based on the use of supersonic plasma flow from the ablation stage of an inverse wire array z-pinch, for studies of shocks in magnetized high energy density physics plasmas in a well-defined and diagnosable 1-D interaction geometry. The mechanism of flow generation ensures that the plasma flow (Re M $ 50, M S $ 5, M A $ 8, V flow % 100 km/s) has a frozen-in magnetic field at a level sufficient to affect shocks formed by its interaction with obstacles. It is found that in addition to the expected accumulation of stagnated plasma in a thin layer at the surface of a planar obstacle, the presence of the magnetic field leads to the formation of an additional detached density jump in the upstream plasma, at a distance of $c/x pi from the obstacle. Analysis of the data obtained with Thomson scattering, interferometry, and local magnetic probes suggests that the sub-shock develops due to the pile-up of the magnetic flux advected by the plasma flow. V C 2014 AIP Publishing LLC. [http://dx.