Publications
311 results found
Merlini S, Hare JD, Burdiak GC, et al., 2023, Radiative cooling effects on reverse shocks formed by magnetized supersonic plasma flows, Physics of Plasmas, Vol: 30, ISSN: 1070-664X
We study the structure of reverse shocks formed by the collision of supersonic, magnetized plasma flows driven by an inverse (or exploding) wire array with a planar conducting obstacle. We observe that the structure of these reverse shocks varies dramatically with wire material, despite the similar upstream flow velocities and mass densities. For aluminum wire arrays, the shock is sharp and well-defined, consistent with magneto-hydrodynamic theory. In contrast, we do not observe a well-defined shock using tungsten wires, and instead we see a broad region dominated by density fluctuations on a wide range of spatial scales. We diagnose these two very different interactions using interferometry, Thomson scattering, shadowgraphy, and a newly developed imaging refractometer that is sensitive to small deflections of the probing laser corresponding to small-scale density perturbations. We conclude that the differences in shock structure are most likely due to radiative cooling instabilities, which create small-scale density perturbations elongated along magnetic field lines in the tungsten plasma. These instabilities grow more slowly and are smoothed by thermal conduction in the aluminum plasma.
Russell DR, Burdiak GC, Carroll-Nellenback JJ, et al., 2023, Observation of subcritical shocks in a collisional laboratory plasma: scale dependence near the resistive length, Journal of Plasma Physics, Vol: 89, ISSN: 0022-3778
We present a study of subcritical shocks in a highly collisional laboratory plasma with a dynamically significant magnetic field. Shocks were produced by placing cylindrical obstacles into the supermagnetosonic ( MMS∼1.9 ) outflow from an inverse wire array z-pinch at the MAGPIE pulsed power facility ( ne∼8.5×1017cm−3 , v∼45kms−1 ). We demonstrate the existence of subcritical shocks in this regime and find that secondary stagnation shocks form in the downstream which we infer from interferometry and optical Thomson scattering measurements are hydrodynamic in nature. The subcritical shock width is found to be approximately equal to the resistive diffusion length and we demonstrate the absence of a jump in hydrodynamic parameters. Temperature measurements by collective optical Thomson scattering showed little temperature change across the subcritical shock ( <10% of the ion kinetic energy) which is consistent with a balance between adiabatic and Ohmic heating and radiative cooling. We demonstrate the absence of subcritical shocks when the obstacle diameter is less than the resistive diffusion length due to decoupling of the magnetic field from the plasma. These findings are supported by magnetohydrodynamic simulations using the Gorgon and AstroBEAR codes and discrepancies between the simulations and experiment are discussed.
Valenzuela-Villaseca V, Suttle LG, Suzuki-Vidal F, et al., 2023, Characterization of quasi-Keplerian, differentially rotating, free-boundary laboratory plasmas, Physical Review Letters, Vol: 130, ISSN: 0031-9007
We present results from pulsed-power driven differentially rotating plasma experiments designed tosimulate physics relevant to astrophysical disks and jets. In these experiments, angular momentum is injectedby the ram pressure of the ablation flows from a wire array Z pinch. In contrast to previous liquid metal andplasma experiments, rotation is not driven by boundary forces. Axial pressure gradients launch a rotatingplasma jet upward, which is confined by a combination of ram, thermal, and magnetic pressure of asurrounding plasma halo. The jet has subsonic rotation, with a maximum rotation velocity 23 3 km=s. Therotational velocity profile is quasi-Keplerian with a positive Rayleigh discriminant κ2 ∝ r−2.8 0.8 rad2=s2.The plasma completes 0.5–2 full rotations in the experimental time frame (∼150 ns).
Datta R, Russell DR, Tang I, et al., 2022, The structure of 3-D collisional magnetized bow shocks in pulsed-power-driven plasma flows, Journal of Plasma Physics, Vol: 88, ISSN: 0022-3778
We investigate three-dimensional (3-D) bow shocks in a highly collisional magnetized aluminium plasma, generated during the ablation phase of an exploding wire array on the MAGPIE facility (1.4 MA, 240 ns). Ablation of plasma from the wire array generates radially diverging, supersonic ( MS∼7 ), super-Alfvénic ( MA>1 ) magnetized flows with frozen-in magnetic flux ( RM≫1 ). These flows collide with an inductive probe placed in the flow, which serves both as the obstacle that generates the magnetized bow shock, and as a diagnostic of the advected magnetic field. Laser interferometry along two orthogonal lines of sight is used to measure the line-integrated electron density. A detached bow shock forms ahead of the probe, with a larger opening angle in the plane parallel to the magnetic field than in the plane normal to it. Since the resistive diffusion length of the plasma is comparable to the probe size, the magnetic field decouples from the ion fluid at the shock front and generates a hydrodynamic shock, whose structure is determined by the sonic Mach number, rather than the magnetosonic Mach number of the flow. The 3-D simulations performed using the resistive magnetohydrodynamic (MHD) code Gorgon confirm this picture, but under-predict the anisotropy observed in the shape of the experimental bow shock, suggesting that non-MHD mechanisms may be important for modifying the shock structure.
Russell D, Burdiak G, Carroll-Nellenback JJ, et al., 2022, Perpendicular subcritical shock structure in a collisional plasma experiment, Physical Review Letters, Vol: 129, ISSN: 0031-9007
We present a study of perpendicular subcritical shocks in a collisional laboratory plasma. Shocks areproduced by placing obstacles into the supermagnetosonic outflow from an inverse wire array z pinch. Wedemonstrate the existence of subcritical shocks in this regime and find that secondary shocks form in thedownstream. Detailed measurements of the subcritical shock structure confirm the absence of ahydrodynamic jump. We calculate the classical (Spitzer) resistive diffusion length and show that it isapproximately equal to the shock width. We measure little heating across the shock (< 10% of the ionkinetic energy) which is consistent with an absence of viscous dissipation.
Datta R, Russell DR, Tang I, et al., 2022, Time-resolved velocity and ion sound speed measurements from simultaneous bow shock imaging and inductive probe measurements, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 93, ISSN: 0034-6748
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- Citations: 3
Markwick RN, Frank A, Carroll-Nellenback J, et al., 2022, Morphology of shocked lateral outflows in colliding hydrodynamic flows, Physics of Plasmas, Vol: 29, ISSN: 1070-664X
Supersonic interacting flows occurring in phenomena, such as protostellar jets, give rise to strong shocks and have been demonstrated in several laboratory experiments. To study such colliding flows, we use the AstroBEAR AMR code to conduct hydrodynamic simulations in three dimensions. We introduce variations in the flow parameters of density, velocity, and cross-sectional radius of the colliding flows in order to study the propagation and conical shape of the bow shock formed by collisions between two, not necessarily symmetric, hypersonic flows. We find that the motion of the interaction region is driven by imbalances in ram pressure between the two flows, while the conical structure of the bow shock is a result of shocked lateral outflows being deflected from the horizontal when the flows are of differing cross sections.
Halliday JWD, Crilly A, Chittenden J, et al., 2022, Investigating radiatively driven, magnetized plasmas with a university scale pulsed-power generator, Physics of Plasmas, Vol: 29, Pages: 1-13, ISSN: 1070-664X
We present first results from a novel experimental platform which is able toaccess physics relevant to topics including indirect-drive magnetised ICF;laser energy deposition; various topics in atomic physics; and laboratoryastrophysics (for example the penetration of B-fields into HED plasmas). Thisplatform uses the X-Rays from a wire array Z-Pinch to irradiate a silicontarget, producing an outflow of ablated plasma. The ablated plasma expands intoambient, dynamically significant B-fields (~5 T) which are supported by thecurrent flowing through the Z-Pinch. The outflows have a well-defined(quasi-1D) morphology, enabling the study of fundamental processes typicallyonly available in more complex, integrated schemes. Experiments were fielded onthe MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time). On this machine awire array Z-Pinch produces an X-Ray pulse carrying a total energy of ~15 kJover ~30 ns. This equates to an average brightness temperature of around 10 eVon-target.
Halliday JWD, Crilly A, Chittenden J, et al., 2022, An Experimental Study of Magnetic Flux Penetration in Radiatively Driven Plasma Flows, ISSN: 0730-9244
In this talk we present measurements from a novel platform in which the X-Rays from a wire-array Z-Pinch irradiate a silicon target, producing an outflow of ablated silicon plasma. This ablated plasma expands into ambient, dynamically significant magnetic fields (B ∼ 5 T) which are supported by the current flowing through the Z-Pinch.
Russell DR, Tubman ER, Halliday JWD, et al., 2022, Radiatively cooled shocks in jets at the MAGPIE pulsed-power facility
Halliday JWD, Bland SN, Hare JD, et al., 2021, A time-resolved imaging system for the diagnosis of x-ray self-emission in high energy density physics experiments, Review of Scientific Instruments, Vol: 92, Pages: 123507-123507, ISSN: 0034-6748
A diagnostic capable of recording spatially and temporally resolved x-ray self-emission data was developed to characterize experiments on the MAGPIE pulsed-power generator. The diagnostic used two separate imaging systems: a pinhole imaging system with two-dimensional spatial resolution and a slit imaging system with one-dimensional spatial resolution. The two-dimensional imaging system imaged light onto the image plate. The one-dimensional imaging system imaged light onto the same piece of image plate and a linear array of silicon photodiodes. This design allowed the cross-comparison of different images, allowing a picture of the spatial and temporal distribution of x-ray self-emission to be established. The design was tested in a series of pulsed-power-driven magnetic-reconnection experiments.
Markwick RN, Frank A, Carroll-Nellenback J, et al., 2021, Cooling and instabilities in colliding flows, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 508, Pages: 2266-2278, ISSN: 0035-8711
Suttle LG, Hare JD, Halliday JWD, et al., 2021, Collective optical Thomson scattering in pulsed-power driven high energy density physics experiments (invited), Review of Scientific Instruments, Vol: 92, Pages: 033542-1-033542-8, ISSN: 0034-6748
Optical collective Thomson scattering (TS) is used to diagnose magnetized high energy density physics experiments at the Magpie pulsedpower generator at Imperial College London. The system uses an amplified pulse from the second harmonic of a Nd:YAG laser (3 J, 8 ns, 532 nm) to probe a wide diversity of high-temperature plasma objects, with densities in the range of 1017–1019 cm−3 and temperatures between 10 eV and a few keV. The scattered light is collected from 100 μm-scale volumes within the plasmas, which are imaged onto optical fiber arrays. Multiple collection systems observe these volumes from different directions, providing simultaneous probing with different scattering K-vectors (and different associated α-parameters, typically in the range of 0.5–3), allowing independent measurements of separate velocity components of the bulk plasma flow. The fiber arrays are coupled to an imaging spectrometer with a gated intensified charge coupled device. The spectrometer is configured to view the ion-acoustic waves of the collective Thomson scattered spectrum. Fits to the spectra with the theoretical spectral density function S(K, ω) yield measurements of the local plasma temperatures and velocities. Fitting is constrained by independent measurements of the electron density from laser interferometry and the corresponding spectra for different scattering vectors.This TS diagnostic has been successfully implemented on a wide range of experiments, revealing temperature and flow velocity transitions across magnetized shocks, inside rotating plasma jets and imploding wire arrays, as well as providing direct measurements of drift velocitiesinside a magnetic reconnection current sheet.
Hare J, Burdiak G, Merlini S, et al., 2021, An imaging refractometer for density fluctuation measurements in high energy density plasmas, Review of Scientific Instruments, Vol: 92, ISSN: 0034-6748
We report on a recently developed laser-probing diagnostic which allows direct measurements of ray-deflection anglesin one axis, whilst retaining imaging capabilities in the other axis. This allows us to measure the spectrum of angulardeflections from a laser beam which passes though a turbulent high-energy-density plasma. This spectrum containsinformation about the density fluctuations within the plasma, which deflect the probing laser over a range of angles. Wecreate synthetic diagnostics using ray-tracing to compare this new diagnostic with standard shadowgraphy and schlierenimaging approaches, which demonstrates the enhanced sensitivity of this new diagnostic over standard techniques. Wepresent experimental data from turbulence behind a reverse shock in a plasma and demonstrate that this technique canmeasure angular deflections between 0.06 and 34 mrad, corresponding to a dynamic range of over 500.
Blackman EG, Lebedev SV, 2020, Persistent mysteries of jet engines, formation, propagation, and particle acceleration: have they been addressed experimentally?, Publisher: arXiv
The physics of astrophysical jets can be divided into three regimes: (i)engine and launch (ii) propagation and collimation, (iii) dissipation andparticle acceleration. Since astrophysical jets comprise a huge range of scalesand phenomena, practicality dictates that most studies of jets intentionally orinadvertently focus on one of these regimes, and even therein, one body of workmay be simply boundary condition for another. We first discuss long standingpersistent mysteries that pertain the physics of each of these regimes,independent of the method used to study them. This discussion makes contactwith frontiers of plasma astrophysics more generally. While observationstheory, and simulations, and have long been the main tools of the trade, whatabout laboratory experiments? Jet related experiments have offered controlledstudies of specific principles, physical processes, and benchmarks fornumerical and theoretical calculations. We discuss what has been done to dateon these fronts. Although experiments have indeed helped us to understandcertain processes, proof of principle concepts, and benchmarked codes, theyhave yet to solved an astrophysical jet mystery on their own. A challenge isthat experimental tools used for jet-related experiments so far, are typicallynot machines originally designed for that purpose, or designed with specificastrophysical mysteries in mind. This presents an opportunity for a differentway of thinking about the development of future platforms: start with theastrophysical mystery and build an experiment to address it.
Hare JD, Burdiak GC, Merlini S, et al., 2020, An imaging refractometer for density fluctuation measurements in high energy density plasmas, Publisher: arXiv
We report on a recently developed laser-based diagnostic which allows directmeasurements of ray-deflection angles in one axis, whilst retaining imagingcapabilities in the other axis. This allows us to measure the spectrum ofangular deflections from a laser beam which passes though a turbulenthigh-energy-density plasma. This spectrum contains information about thedensity fluctuations within the plasma, which deflect the probing laser over arange of angles. The principle of this diagnostic is described, along with ourspecific experimental realisation. We create synthetic diagnostics usingray-tracing to compare this new diagnostic with standard shadowgraphy andschlieren imaging approaches, which demonstrates the enhanced sensitivity ofthis new diagnostic over standard techniques. We present experimental data fromturbulence behind a reverse shock in a plasma and demonstrate that thistechnique can measure angular deflections between 0.05 and 34 mrad,corresponding to a dynamic range of over 500.
Suttle LG, Burdiak GC, Cheung CL, et al., 2020, Interactions of magnetized plasma flows in pulsed-power driven experiments, Plasma Physics and Controlled Fusion, Vol: 62, ISSN: 0741-3335
A supersonic flow of magnetized plasma is produced by the application of a 1 MA-peak, 500 ns current pulse to a cylindrical arrangement of parallel wires, known as an inverse wire array. The plasma flow is produced by the J × B acceleration of the ablated wire material, and a magnetic field of several Tesla is embedded at source by the driving current. This setup has been used for a variety of experiments investigating the interactions of magnetized plasma flows. In experiments designed to investigate magnetic reconnection, the collision of counter-streaming flows, carrying oppositely directed magnetic fields, leads to the formation of a reconnection layer in which we observe ions reaching temperatures much greater than predicted by classical heating mechanisms. The breakup of this layer under the plasmoid instability is dependent on the properties of the inflowing plasma, which can be controlled by the choice of the wire array material. In other experiments, magnetized shocks were formed by placing obstacles in the path of the magnetized plasma flow. The pile-up of magnetic flux in front of a conducting obstacle produces a magnetic precursor acting on upstream electrons at the distance of the ion inertial length. This precursor subsequently develops into a steep density transition via ion-electron fluid decoupling. Obstacles which possess a strong private magnetic field affect the upstream flow over a much greater distance, providing an extended bow shock structure. In the region surrounding the obstacle the magnetic pressure holds off the flow, forming a void of plasma material, analogous to the magnetopause around planetary bodies with self-generated magnetic fields.
Lebedev S, Spielman RB, Li X, 2019, Editorial for special issue on Z-pinches, MATTER AND RADIATION AT EXTREMES, Vol: 4, ISSN: 2468-2047
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- Citations: 2
Fogerty E, Liu B, Frank A, et al., 2019, Hydrodynamic and magnetohydrodynamic simulations of wire turbulence, High Energy Density Physics, Vol: 33, Pages: 1-9, ISSN: 1574-1818
We report on simulations of laboratory experiments in which magnetized supersonic flowsare driven through a wire mesh. The goal of the study was to investigate the ability of such aconfiguration to generate supersonic, MHD turbulence. We first report on the morphologicalstructures that develop in both magnetized and non-magnetized cases. We then analyze the flowusing a variety of statistical measures, including power spectra and probability distributionfunctions of the density. Using these results we estimate the sonic mach number in the flowsdownstream of the wire mesh. We find the initially hypersonic (Ms = 20) planar shock throughthe wire mesh does lead to downstream turbulent conditions. However, in both magnetizedand non-magnetized cases, the resultant turbulence was marginally supersonic to transonic(Ms ∼ 1), and highly anisotropic in structure.
Hare JD, MacDonald J, Bland SN, et al., 2019, Two-colour interferometry and Thomson scattering measurements of a plasma gun, Publisher: IOP PUBLISHING LTD
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- Citations: 14
Hare JD, MacDonald J, Bland S, et al., 2019, Two-colour interferometry and Thomson scattering measurements of a plasma gun, Plasma Physics and Controlled Fusion, Vol: 61, ISSN: 0741-3335
We present experimental measurements of a pulsed plasma gun, using two-colour imaging laser interferometry and spatially resolved Thomson scattering. Interferometry measurements give an electron density ne ≈ 2.7 × 1017 cm−3 at the centre of the plasma plume, at 5 mm from the plasma gun nozzle. The Thomson scattered light is collected from two probing angles allowed us to simultaneously measure the collective and non-collective spectrum of the electron feature from the same spatial locations. The inferred electron densities from the location of the electron plasma waves is in agreement with interferometry. The electron temperatures inferred from the two spectra are not consistent, with Te ≈ 10 eV for non-collective scattering and Te ≈ 30 eV for collective scattering. We discuss various broadening mechanisms such as finite aperture effects, density gradients within the collective volume and collisional broadening to account for some of this discrepancy. We also note the significant red/blue asymmetry of the electron plasma waves in the collective scattering spectra, which could relate to kinetic effects distorting the distribution function of the electrons.
Palmer CAJ, Campbell PT, Ma Y, et al., 2019, Field reconstruction from proton radiography of intense laser driven magnetic reconnection, Publisher: AIP Publishing, ISSN: 1070-664X
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- Citations: 12
Lebedev SV, Frank A, Ryutov DD, 2019, Exploring astrophysics-relevant magnetohydrodynamics with pulsed-power laboratory facilities, Reviews of Modern Physics, Vol: 91, ISSN: 0034-6861
Laboratory facilities employing high pulsed currents and voltages, and called generally “pulsedpower facilities,” allow experimenters to produce a variety of hydrodynamical structures replicating, often in a scalable fashion, a broad range of dynamical astrophysical phenomena. Among these are astrophysical jets and outflows, astrophysical blast waves, magnetized radiatively dominated flows, and, more recently, aspects of simulated accretion disks. The magnetic field thought to play a significant role in most of the aforementioned objects is naturally present and controllable in pulsedpower environments. The size of the objects produced in pulsed-power experiments ranges from a centimeter to tens of centimeters, thereby allowing the use of a variety of diagnostic techniques. In a number of situations astrophysical morphologies can be replicated down to the finest structures. The configurations and their parameters are highly reproducible; one can vary them to isolate the most important phenomena and thereby help in developing astrophysical models. This approach has emerged as a useful tool in the quest to better understand magnetohydrodynamical effects in astronomical environments. The present review summarizes the progress made during the last decade and is designed to help readers identify and, perhaps, implement new experiments in this growing research area. Techniques used for the generation and characterization of the flows are described.
Suzuki Vidal F, Clayson T, Lebedev S, et al., 2018, Inverse liner z-pinch: an experimental pulsed power platform for studying radiative shocks, IEEE Transactions on Plasma Science, Vol: 46, Pages: 3734-3740, ISSN: 0093-3813
We present a new experimental platform for studying radiative shocks using an ``inverse liner z-pinch'' configuration. This platform was tested on the MAGPIE pulsed power facility (~1 MA with a rise time of ~240 ns) at Imperial College London, U.K. Current is discharged through a thin-walled metal tube (a liner) embedded in a low-density gas-fill and returned through a central post. The resulting magnetic pressure inside the liner launched a cylindrically symmetric, expanding radiative shock into the gas-fill at ~10 km/s. This experimental platform provides good diagnostic access, allowing multiframe optical self-emission imaging, laser interferometry, and optical emission spectrography to be fielded. Results from experiments with an Argon gas-fill initially at 0.04 mg/cm³are presented, demonstrating the successful production of cylindrically symmetric, expanding shocks that exhibit radiative effects such as the formation of a radiative precursor.
Wu J, Lu Y, Sun F, et al., 2018, Preconditioned wire array Z-pinches driven by a double pulse current generator, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 60, ISSN: 0741-3335
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- Citations: 20
Rigby A, Cruz F, Albertazzi B, et al., 2018, Electron acceleration by wave turbulence in a magnetized plasma, Nature Physics, Vol: 14, Pages: 475-479, ISSN: 1745-2473
Astrophysical shocks are commonly revealed by the non-thermal emission of energetic electrons accelerated in situ 1-3 . Strong shocks are expected to accelerate particles to very high energies 4-6 ; however, they require a source of particles with velocities fast enough to permit multiple shock crossings. While the resulting diffusive shock acceleration 4 process can account for observations, the kinetic physics regulating the continuous injection of non-thermal particles is not well understood. Indeed, this injection problem is particularly acute for electrons, which rely on high-frequency plasma fluctuations to raise them above the thermal pool 7,8 . Here we show, using laboratory laser-produced shock experiments, that, in the presence of a strong magnetic field, significant electron pre-heating is achieved. We demonstrate that the key mechanism in producing these energetic electrons is through the generation of lower-hybrid turbulence via shock-reflected ions. Our experimental results are analogous to many astrophysical systems, including the interaction of a comet with the solar wind 9 , a setting where electron acceleration via lower-hybrid waves is possible.
Suttle LG, Hare JD, Lebedev SV, et al., 2018, Ion heating and magnetic flux pile-up in a magnetic reconnection experiment with super-Alfvenic plasma inflows, Physics of Plasmas, Vol: 25, ISSN: 1070-664X
This work presents a magnetic reconnection experiment in which the kinetic, magnetic, and thermal properties of the plasma each play an important role in the overall energy balance and structure of the generated reconnection layer. Magnetic reconnection occurs during the interaction of continuous and steady flows of super-Alfvénic, magnetized, aluminum plasma, which collide in a geometry with two-dimensional symmetry, producing a stable and long-lasting reconnection layer. Optical Thomson scattering measurements show that when the layer forms, ions inside the layer are more strongly heated than electrons, reaching temperatures of Ti∼Z⎯⎯⎯Te≳300 eV—much greater than can be expected from strong shock and viscous heating alone. Later in time, as the plasma density in the layer increases, the electron and ion temperatures are found to equilibrate, and a constant plasma temperature is achieved through a balance of the heating mechanisms and radiative losses of the plasma. Measurements from Faraday rotation polarimetry also indicate the presence of significant magnetic field pile-up occurring at the boundary of the reconnection region, which is consistent with the super-Alfvénic velocity of the inflows.
Hare JD, Suttle LG, Lebedev SV, et al., 2018, An Experimental Platform for Pulsed-Power Driven Magnetic Reconnection, Physics of Plasmas, Vol: 25, ISSN: 1070-664X
We describe a versatile pulsed-power driven platform for magneticreconnection experiments, based on exploding wire arrays driven in parallel[Suttle, L. G. et al. PRL, 116, 225001]. This platform produces inherentlymagnetised plasma flows for the duration of the generator current pulse (250ns), resulting in a long-lasting reconnection layer. The layer exists for longenough to allow evolution of complex processes such as plasmoid formation andmovement to be diagnosed by a suite of high spatial and temporal resolutionlaser-based diagnostics. We can access a wide range of magnetic reconnectionregimes by changing the wire material or moving the electrodes inside the wirearrays. We present results with aluminium and carbon wires, in which theparameters of the inflows and the layer which forms are significantlydifferent. By moving the electrodes inside the wire arrays, we change howstrongly the inflows are driven. This enables us to study both symmetricreconnection in a range of different regimes, and asymmetric reconnection.
Hare JD, Lebedev SV, Suttle LG, et al., 2017, Formation and structure of a current sheet in pulsed-power driven magnetic reconnection experiments, Physics of Plasmas, Vol: 24, ISSN: 1070-664X
We describe magnetic reconnection experiments using a new, pulsed-powerdriven experimental platform in which the inflows are super-sonic butsub-Alfv\'enic.The intrinsically magnetised plasma flows are long lasting,producing a well-defined reconnection layer that persists over manyhydrodynamic time scales.The layer is diagnosed using a suite of highresolution laser based diagnostics which provide measurements of the electrondensity, reconnecting magnetic field, inflow and outflow velocities and theelectron and ion temperatures.Using these measurements we observe a balancebetween the power flow into and out of the layer, and we find that the heatingrates for the electrons and ions are significantly in excess of the classicalpredictions. The formation of plasmoids is observed in laser interferometry andoptical self-emission, and the magnetic O-point structure of these plasmoids isconfirmed using magnetic probes.
Suzuki Vidal F, Clayson T, Swadling GF, et al., 2017, Counter-propagating radiative shock experiments on the Orion laser, Physical Review Letters, Vol: 119, ISSN: 1079-7114
We present new experiments to study the formation of radiative shocks and the interaction between two counterpropagating radiative shocks. The experiments are performed at the Orion laser facility, which is used to drive shocks in xenon inside large aspect ratio gas cells. The collision between the two shocks and their respective radiative precursors, combined with the formation of inherently three-dimensional shocks, provides a novel platform particularly suited for the benchmarking of numerical codes. The dynamics of the shocks before and after the collision are investigated using point-projection x-ray backlighting while, simultaneously, the electron density in the radiative precursor was measured via optical laser interferometry. Modeling of the experiments using the 2D radiation hydrodynamic codes nym and petra shows very good agreement with the experimental results.
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