Imperial College London

DrJackHare

Faculty of Natural SciencesDepartment of Physics

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+44 (0)20 7594 5659jdhare CV

 
 
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Location

 

739BBlackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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38 results found

Pearcy JA, Rosenberg MJ, Johnson TM, Sutcliffe GD, Reichelt BL, Hare JD, Loureiro NF, Petrasso RD, Li CKet al., 2024, Experimental Evidence of Plasmoids in High-β Magnetic Reconnection., Phys Rev Lett, Vol: 132

Magnetic reconnection is a ubiquitous and fundamental process in plasmas by which magnetic fields change their topology and release magnetic energy. Despite decades of research, the physics governing the reconnection process in many parameter regimes remains controversial. Contemporary reconnection theories predict that long, narrow current sheets are susceptible to the tearing instability and split into isolated magnetic islands (or plasmoids), resulting in an enhanced reconnection rate. While several experimental observations of plasmoids in the regime of low-to-intermediate β (where β is the ratio of plasma thermal pressure to magnetic pressure) have been made, there is a relative lack of experimental evidence for plasmoids in the high-β reconnection environments which are typical in many space and astrophysical contexts. Here, we report strong experimental evidence for plasmoid formation in laser-driven high-β reconnection experiments.

Journal article

Merlini S, Hare JD, Burdiak GC, Halliday JWD, Ciardi A, Chittenden JP, Clayson T, Crilly AJ, Eardley SJ, Marrow KE, Russell DR, Smith RA, Stuart N, Suttle LG, Tubman ER, Valenzuela-Villaseca V, Varnish TWO, Lebedev SVet 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.

Journal article

Datta R, Angel J, Greenly JB, Bland SN, Chittenden JP, Lavine ES, Potter WM, Robinson D, Varnish TWO, Wong E, Hammer DA, Kusse BR, Hare JDet al., 2023, Plasma flows during the ablation stage of an over-massed pulsed-power-driven exploding planar wire array, PHYSICS OF PLASMAS, Vol: 30, ISSN: 1070-664X

Journal article

Russell DR, Burdiak GC, Carroll-Nellenback JJ, Halliday JWD, Hare JD, Merlini S, Suttle LG, Valenzuela-Villaseca V, Eardley SJ, Fullalove JA, Rowland GC, Smith RA, Frank A, Hartigan P, Velikovich AL, Chittenden JP, Lebedev SVet 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.

Journal article

Valenzuela-Villaseca V, Suttle LG, Suzuki-Vidal F, Halliday JWD, Merlini S, Russell DR, Tubman ER, Hare JD, Chittenden JP, Koepke ME, Blackman EG, Lebedev SVet 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).

Journal article

Jahanbakhsh S, Hare JD, Meister H, Ingesson C, Majewski M, Penzel F, Schmitt S, Walach U, Dubois Met al., 2023, Calibration and thermal test results of prototype bolometer sensors for ITER fusion reactor, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 94, ISSN: 0034-6748

Journal article

Datta R, Russell DR, Tang I, Clayson T, Suttle LG, Chittenden JP, Lebedev S, Hare JDet 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.

Journal article

Russell D, Burdiak G, Carroll-Nellenback JJ, Halliday J, Hare J, Merlini S, Suttle L, Valenzuela-Villaseca V, Eardley S, Fullalove J, Rowland G, Smith R, Frank A, Hartigan P, Velikovich AL, Chittenden J, Lebedev Set 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.

Journal article

Datta R, Russell DR, Tang I, Clayson T, Suttle LG, Chittenden JP, Lebedev S, Hare JDet 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

Journal article

Halliday JWD, Bland SN, Hare JD, Parker S, Suttle LG, Russell DR, Lebedev SVet 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.

Journal article

Filippov ED, Makarov SS, Burdonov KF, Yao W, Revet G, Beard J, Bolanos S, Chen SN, Guediche A, Hare J, Romanovsky D, Skobelev IY, Starodubtsev M, Ciardi A, Pikuz SA, Fuchs Jet al., 2021, Enhanced X-ray emission arising from laser-plasma confinement by a strong transverse magnetic field, SCIENTIFIC REPORTS, Vol: 11, ISSN: 2045-2322

Journal article

Suttle LG, Hare JD, Halliday JWD, Merlini S, Russell DR, Tubman ER, Valenzuela-Villaseca V, Rozmus W, Bruulsema C, Lebedev SVet 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.

Journal article

Hare J, Burdiak G, Merlini S, Chittenden J, Clayson T, Crilly A, Halliday J, Russell D, Smith R, Stuart N, Suttle L, Lebedev Set 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.

Journal article

Hare JD, Burdiak GC, Merlini S, Chittenden JP, Clayson T, Crilly AJ, Halliday JWD, Russell DR, Smith RA, Stuart N, Suttle LG, Lebedev SVet 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.

Working paper

Suttle LG, Burdiak GC, Cheung CL, Clayson T, Halliday JWD, Hare JD, Rusli S, Russell DR, Tubman ER, Ciardi A, Loureiro NF, Li J, Frank A, Lebedev Set 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.

Journal article

Hare JD, MacDonald J, Bland S, Dranczewski J, Halliday J, Lebedev S, Suttle L, Tubman E, Rozmus Wet 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.

Journal article

Hare JD, MacDonald J, Bland SN, Dranczewski J, Halliday JWD, Lebedev S, Suttle LG, Tubman ER, Rozmus Wet al., 2019, Two-colour interferometry and Thomson scattering measurements of a plasma gun, Publisher: IOP PUBLISHING LTD

Working paper

Suzuki Vidal F, Clayson T, Lebedev S, Hare J, Halliday J, Suttle L, Tubman Eet 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.

Journal article

Suttle LG, Hare JD, Lebedev SV, Ciardi A, Loureiro NF, Burdiak GC, Chittenden JP, Clayson T, Halliday JWD, Niasse N, Russell D, Suzuki-Vidal F, Tubman E, Lane T, Ma J, Robinson T, Smith RA, Stuart Net 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.

Journal article

Hare J, Suttle L, Lebedev S, Loureiro N, Ciardi A, Chittenden J, Clayson T, Eardley S, Garcia C, Halliday J, Robinson T, Smith R, Stuart N, Suzuki-Vidal F, Tubman Eet 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 magnetic reconnection experiments, based on the exploding wire arrays driven in parallel [Suttle et al., Phys. Rev. Lett. 116, 225001 (2016)]. This platform produces inherently magnetised plasma flows for the duration of the generator current pulse (250 ns), resulting in a long-lasting reconnection layer. The layer exists for long enough to allow the evolution of complex processes such as plasmoid formation and movement to be diagnosed by a suite of high spatial and temporal resolution laser-based diagnostics. We can access a wide range of magnetic reconnection regimes by changing the wire material or moving the electrodes inside the wire arrays. We present results with aluminium and carbon wires, in which the parameters of the inflows and the layer that forms are significantly different. By moving the electrodes inside the wire arrays, we change how strongly the inflows are driven. This enables us to study both symmetric reconnection in a range of different regimes and asymmetric reconnection.

Journal article

Hare JD, Lebedev SV, Suttle LG, Loureiro NF, Ciardi A, Burdiak GC, Chittenden JP, Clayson T, Eardley SJ, Garcia C, Halliday JWD, Niasse N, Robinson T, Smith RA, Stuart N, Suzuki-Vidal F, Swadling GF, Ma J, Wu Jet 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.

Journal article

Hare J, 2017, FORMATION AND STRUCTURE OF A CURRENT SHEET IN PULSED-POWER DRIVEN MAGNETIC RECONNECTION EXPERIMENTS, Physics of Plasmas, ISSN: 1070-664X

Journal article

Burdiak GC, Lebedev SV, Bland SN, Clayson T, Hare J, Suttle L, Suzuki-Vidal F, Garcia DC, Chittenden JP, Bott-Suzuki S, Ciardi A, Frank A, Lane TSet al., 2017, The structure of bow shocks formed by the interaction of pulsed-power driven magnetised plasma flows with conducting obstacles, PHYSICS OF PLASMAS, Vol: 24, ISSN: 1070-664X

We present an experimental study of the development and structure of bow shocks produced by the interaction of a magnetised, collisional, super-Alfvénic plasma flow with conducting cylindrical obstacles. The plasma flow with an embedded, frozen-in magnetic field (ReM ∼ 20) is produced by the current-driven ablation of fine aluminium wires in an inverse, exploding wire array z-pinch. We show that the orientation of the embedded field with respect to the obstacles has a dramatic effect on the bow shock structure. When the field is aligned with the obstacle, a sharp bow shock is formed with a global structure that is determined simply by the fast magneto-sonic Mach number. When the field is orthogonal to the obstacle, magnetic draping occurs. This leads to the growth of a magnetic precursor and the subsequent development of a magnetised bow shock that is mediated by two-fluid effects, with an opening angle and a stand-off distance, that are both many times larger than in the parallel geometry. By changing the field orientation, we change the fluid regime and physical mechanisms that are responsible for the development of the bow shocks. MHD simulations show good agreement with the structure of well-developed bow shocks. However, collisionless, two-fluid effects will need to be included within models to accurately reproduce the development of the shock with an orthogonal B-field.

Journal article

Hare JD, Suttle L, Lebedev SV, Loureiro NF, Ciardi A, Burdiak GC, Chittenden JP, Clayson T, Garcia C, Niasse N, Robinson T, Smith RA, Stuart N, Suzuki-Vidal F, Swadling GF, Ma J, Wu J, Yang Qet al., 2017, Anomalous heating and plasmoid formation in a driven magnetic reconnection experiment, Physical Review Letters, Vol: 118, ISSN: 0031-9007

We present a detailed study of magnetic reconnection in a quasi-two-dimensional pulsed-power driven laboratory experiment. Oppositely directed magnetic fields (B=3  T), advected by supersonic, sub-Alfvénic carbon plasma flows (Vin=50  km/s), are brought together and mutually annihilate inside a thin current layer (δ=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 (Te=100  eV, Ti=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.

Journal article

Suttle LG, Hare JD, Lebedev SV, Swadling GF, Burdiak GC, Ciardi A, Chittenden JP, Loureiro NF, Niasse N, Suzuki Vidal F, Wu J, Yang Q, Clayson T, Frank A, Robinson TS, Smith RA, Stuart Net al., 2016, Structure of a Magnetic Flux Annihilation Layer Formed by the Collision of Supersonic, Magnetized Plasma Flows, Physical Review Letters, Vol: 116, ISSN: 1079-7114

We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counterstreaming, supersonic and magnetized aluminum plasma flows. The antiparallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure—two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature (Ti∼Z¯Te, with average ionization Z¯=7). Analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of the inflowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities.

Journal article

Swadling GF, Lebedev SV, Hall GN, Suzuki-Vidal F, Burdiak GC, Pickworth L, De Grouchy P, Skidmore J, Khoory E, Suttle L, Bennett M, Hare JD, Clayson T, Bland SN, Smith RA, Stuart NH, Patankar S, Robinson TS, Harvey-Thompson AJ, Rozmus W, Yuan J, Sheng Let al., 2016, Experimental investigations of ablation stream interaction dynamics in tungsten wire arrays: interpenetration, magnetic field advection, and ion deflection, Physics of Plasmas, Vol: 23, ISSN: 1089-7674

Experiments have been carried out to investigate the collisional dynamics of ablation streams produced by cylindrical wire array z-pinches. A combination of laser interferometric imaging, Thomson scattering, and Faraday rotationimaging has been used to make a range of measurements of the temporal evolution of various plasma and flow parameters. This paper presents a summary of previously published data, drawing together a range of different measurements in order to give an overview of the key results. The paper focuses mainly on the results of experiments with tungsten wire arrays. Early interferometric imagingmeasurements are reviewed, then more recent Thomson scattering measurements are discussed; these measurements provided the first direct evidence of ablation stream interpenetration in a wire array experiment. Combining the data from these experiments gives a view of the temporal evolution of the tungsten stream collisional dynamics. In the final part of the paper, we present new experimental measurements made using an imagingFaraday rotationdiagnostic. These experiments investigated the structure of magnetic fields near the array axis directly; the presence of a magnetic field has previously been inferred based on Thomson scattering measurements of ion deflection near the array axis. Although the Thomson and Faradaymeasurements are not in full quantitative agreement, the Faraday data do qualitatively supports the conjecture that the observed deflections are induced by a static toroidal magnetic field, which has been advected to the array axis by the ablation streams. It is likely that detailed modeling will be needed in order to fully understand the dynamics observed in the experiment.

Journal article

Haerendel G, Suttle L, Lebedev SV, Swadling GF, Hare JD, Burdiak GC, Bland SN, Chittenden JP, Kalmoni N, Frank A, Smith RA, Suzuki-Vidal Fet al., 2016, Stop layer: a flow braking mechanism in space and support from a lab experiment, Plasma Physics and Controlled Fusion, Vol: 58, ISSN: 1361-6587

The paper presents short summaries and a synopsis of two completely independent discoveries of a fast flow braking process, one realized by a laboratory experiment (Lebedev et al 2014 Phys. Plasmas 21 056305), the other by theoretical reasoning stimulated by auroral observation (Haerendel 2015a J. Geophys. Res. Space Phys. 120 1697–714). The first has been described as a magnetically mediated sub-shock forming when a supersonic plasma flow meets a wall. The second tried to describe what happens when a high-beta plasma flow from the central magnetic tail meets the strong near-dipolar field of the magnetosphere. The term stop layer signals that flow momentum and energy are directly coupled to a magnetic perturbation field generated by a Hall current within a layer of the width of c/ω pi and immediately propagated out of the layer by kinetic Alfvén waves. As the laboratory situation is not completely collision-free, energy transfer from ions to electrons and subsequent radiative losses are likely to contribute. A synopsis of the two situations identifies and discusses six points of commonality between the two situations. It is pointed out that the stop layer mechanism can be regarded as a direct reversal of the reconnection process.

Journal article

Burdiak GC, Lebedev SV, Clayson T, Hare JD, Suttle LG, Suzuki-Vidal F, Chittenden JP, Garcia DC, Niasse N, Lane Tet al., 2016, THE EFFECT OF MAGNETIC FIELD ORIENTATION ON THE STRUCTURE AND INTERACTION OF MAGNETISED BOW SHOCKS IN PULSED-POWER DRIVEN EXPERIMENTS, 43rd IEEE International Conference on Plasma Science (ICOPS), Publisher: IEEE

Conference paper

Burdiak GC, Lebedev SV, Clayson T, Hare JD, Suttle LG, Suzuki-Vidal Fet al., 2016, LABORATORY ASTROPHYSICS WITH SUPERSONIC MAGNETISED PLASMAS: EXPERIMENTS ON THE MAGPIE PULSED-POWER FACILITY, 43rd IEEE International Conference on Plasma Science (ICOPS), Publisher: IEEE

Conference paper

Burdiak GC, Lebedev SV, Suzuki-Vidal F, Swadling GF, Bland SN, Niasse N, Suttle L, Bennet M, Hare J, Weinwurm M, Rodriguez R, Gil J, Espinosa Get al., 2015, Cylindrical liner Z-pinch experiments for fusion research and high-energy-density physics, Journal of Plasma Physics, Vol: 81, ISSN: 1469-7807

A gas-filled cylindrical liner z-pinch configuration has been used to drive convergentradiative shock waves into different gases at velocities of 20–50 km s−1. On applicationof the 1.4 MA, 240 ns rise-time current pulse produced by the Magpie generatorat Imperial College London, a series of cylindrically convergent shock waves aresequentially launched into the gas-fill from the inner wall of the liner. This occurswithout any bulk motion of the liner wall itself. The timing and trajectories of theshocks are used as a diagnostic tool for understanding the response of the linerz-pinch wall to a large pulsed current. This analysis provides useful data on theliner resistivity, and a means to test equation of state (EOS) and material strengthmodels within MHD simulation codes. In addition to providing information on linerresponse, the convergent shocks are interesting to study in their own right. The shocksare strong enough for radiation transport to influence the shock wave structure. Inparticular, we see evidence for both radiative preheating of material ahead of theshockwaves and radiative cooling instabilities in the shocked gas. Some preliminaryresults from initial gas-filled liner experiments with an applied axial magnetic fieldare also discussed.

Journal article

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