Imperial College London

ProfessorSergeyLebedev

Faculty of Natural SciencesDepartment of Physics

Professor of Plasma Physics
 
 
 
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Contact

 

+44 (0)20 7594 7748s.lebedev Website

 
 
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Location

 

743Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

307 results found

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, Pages: 225001-225001, ISSN: 0031-9007

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

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

Markwick RN, Frank A, Carroll-Nellenback J, Blackman EG, Hartigan PM, Lebedev SV, Russell DR, Halliday JWD, Suttle LGet al., 2022, Morphology of shocked lateral outflows in colliding hydrodynamic flows, PHYSICS OF PLASMAS, Vol: 29, ISSN: 1070-664X

Journal article

Halliday JWD, Crilly A, Chittenden J, Mancini RC, Merlini S, Rose S, Russell DR, Suttle LG, Valenzuela-Villaseca V, Bland SN, Lebedev SVet 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.

Journal article

Halliday JWD, Crilly A, Chittenden J, Merlini S, Rose S, Russell D, Suttle LG, Mancini RC, Valenzuela-Villaseca V, Bland SN, Lebedev SVet 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.

Conference paper

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

Markwick RN, Frank A, Carroll-Nellenback J, Liu B, Blackman EG, Lebedev S, Hartigan PMet al., 2021, Cooling and instabilities in colliding flows, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 508, Pages: 2266-2278, ISSN: 0035-8711

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

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.

Working paper

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

Lebedev S, Spielman RB, Li X, 2019, Editorial for special issue on Z-pinches, MATTER AND RADIATION AT EXTREMES, Vol: 4, ISSN: 2468-2047

Journal article

Fogerty E, Liu B, Frank A, Carroll-Nellenback J, Lebedev Set 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.

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

Palmer CAJ, Campbell PT, Ma Y, Antonelli L, Bott AFA, Gregori G, Halliday J, Katzir Y, Kordell P, Krushelnick K, Lebedev SV, Montgomery E, Notley M, Carroll DC, Ridgers CP, Schekochihin AA, Streeter MJV, Thomas AGR, Tubman ER, Woolsey N, Willingale Let al., 2019, Field reconstruction from proton radiography of intense laser driven magnetic reconnection, Publisher: AIP Publishing, ISSN: 1070-664X

Conference paper

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

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.

Journal article

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

Rigby A, Cruz F, Albertazzi B, Bamford R, Bell AR, Cross JE, Fraschetti F, Graham P, Hara Y, Kozlowski PM, Kuramitsu Y, Lamb DQ, Lebedev S, Marques JR, Miniati F, Morita T, Oliver M, Reville B, Sakawa Y, Sarkar S, Spindloe C, Trines R, Tzeferacos P, Silva LO, Bingham R, Koenig M, Gregori Get 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.

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 JD, Suttle LG, Lebedev SV, Loureiro NF, Ciardi A, Chittenden JP, Clayson T, Eardley SJ, Garcia C, Halliday JWD, Robinson T, Smith RA, Stuart N, Suzuki-Vidal F, Tubman ERet 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.

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

Suzuki Vidal F, Clayson T, Swadling GF, Lebedev SV, Burdiak GC, Stehlé C, Chaulagain U, Singh RL, Foster JM, Skidmore J, Gumbrell ET, Graham P, Patankar S, Danson C, Spindloe C, Larour J, Kozlova M, Rodriguez R, Gil JM, Espinosa G, Velarde Pet 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.

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

Hansen EC, Frank A, Hartigan P, Lebedev SVet al., 2017, The Shock Dynamics of Heterogeneous YSO Jets: 3D Simulations Meet Multi-epoch Observations, ASTROPHYSICAL JOURNAL, Vol: 837, ISSN: 0004-637X

High-resolution observations of young stellar object (YSO) jets show them to be composed of many small-scale knots or clumps. In this paper, we report results of 3D numerical simulations designed to study how such clumps interact and create morphologies and kinematic patterns seen in emission line observations. Our simulations focus on clump scale dynamics by imposing velocity differences between spherical, over-dense regions, which then lead to the formation of bow shocks as faster clumps overtake slower material. We show that much of the spatial structure apparent in emission line images of jets arises from the dynamics and interactions of these bow shocks. Our simulations show a variety of time-dependent features, including bright knots associated with Mach stems where the shocks intersect, a "frothy" emission structure that arises from the presence of the Nonlinear Thin Shell Instability along the surfaces of the bow shocks, and the merging and fragmentation of clumps. Our simulations use a new non-equilibrium cooling method to produce synthetic emission maps in Hα and [S ii]. These are directly compared to multi-epoch Hubble Space Telescope observations of Herbig–Haro jets. We find excellent agreement between features seen in the simulations and the observations in terms of both proper motion and morphologies. Thus we conclude that YSO jets may be dominated by heterogeneous structures and that interactions between these structures and the shocks they produce can account for many details of YSO jet evolution.

Journal article

Clayson T, Suzuki-Vidal F, Lebedev SV, Swadling GF, Stehle C, Burdiak GC, Foster JM, Skidmore J, Graham P, Gumbrell E, Patankar S, Spindloe C, Chaulagain U, Kozlova M, Larour J, Singh RL, Rodriguez R, Gil JM, Espinosa G, Velarde P, Danson Cet al., 2017, Counter-propagating radiative shock experiments on the Orion laser and the formation of radiative precursors, High Energy Density Physics, Vol: 23, Pages: 60-72, ISSN: 1878-0563

We present results from new experiments to study the dynamics of radiative shocks, reverse shocks and radiative precursors. Laser ablation of a solid piston by the Orion high-power laser at AWE Aldermaston UK was used to drive radiative shocks into a gas cell initially pressurised between 0.1 and 1.0 bar with different noble gases. Shocks propagated at 80 ± 10 km/s and experienced strong radiative cooling resulting in post-shock compressions of ×25 ± 2. A combination of X-ray backlighting, optical self-emission streak imaging and interferometry (multi-frame and streak imaging) were used to simultaneously study both the shock front and the radiative precursor. These experiments present a new configuration to produce counter-propagating radiative shocks, allowing for the study of reverse shocks and providing a unique platform for numerical validation. In addition, the radiative shocks were able to expand freely into a large gas volume without being confined by the walls of the gas cell. This allows for 3-D effects of the shocks to be studied which, in principle, could lead to a more direct comparison to astrophysical phenomena. By maintaining a constant mass density between different gas fills the shocks evolved with similar hydrodynamics but the radiative precursor was found to extend significantly further in higher atomic number gases (∼4 times further in xenon than neon). Finally, 1-D and 2-D radiative-hydrodynamic simulations are presented showing good agreement with the experimental data.

Journal article

Espinosa G, Rodriguez R, Gil JM, Suzuki-Vidal F, Lebedev SV, Ciardi A, Rubiano JG, Martel Pet al., 2017, Influence of atomic kinetics in the simulation of plasma microscopic properties and thermal instabilities for radiative bow shock experiments, PHYSICAL REVIEW E, Vol: 95, ISSN: 2470-0045

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

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