69 results found
Rosenberg MJ, Hernandez JE, Butler N, et al., 2021, The Scattered Light Time-history Diagnostic suite at the National Ignition Facility, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 92, ISSN: 0034-6748
Farmer WA, Rosen MD, Swadling GF, et al., 2021, Investigation of heat transport using directly driven gold spheres, PHYSICS OF PLASMAS, Vol: 28, ISSN: 1070-664X
Farmer WA, Bruulsema C, Swadling GF, et al., 2020, Validation of heat transport modeling using directly driven beryllium spheres, PHYSICS OF PLASMAS, Vol: 27, ISSN: 1070-664X
Fiuza F, Swadling GF, Grassi A, et al., 2020, Electron acceleration in laboratory-produced turbulent collisionless shocks, NATURE PHYSICS, Vol: 16, Pages: 916-+, ISSN: 1745-2473
Swadling GF, Bruulsema C, Fiuza F, et al., 2020, Measurement of Kinetic-Scale Current Filamentation Dynamics and Associated Magnetic Fields in Interpenetrating Plasmas, PHYSICAL REVIEW LETTERS, Vol: 124, ISSN: 0031-9007
Bruulsema C, Rozmus W, Swadling GF, et al., 2020, On the local measurement of electric currents and magnetic fields using Thomson scattering in Weibel-unstable plasmas, PHYSICS OF PLASMAS, Vol: 27, ISSN: 1070-664X
Williams GJ, Patankar S, Mariscal DA, et al., 2020, Laser intensity scaling of the magnetic field from a laser-driven coil target, JOURNAL OF APPLIED PHYSICS, Vol: 127, ISSN: 0021-8979
Higginson DP, Ross JS, Ryutov DD, et al., 2019, Kinetic effects on neutron generation in moderately collisional interpenetrating plasma flows, PHYSICS OF PLASMAS, Vol: 26, ISSN: 1070-664X
Patankar S, Yang ST, Moody JD, et al., 2018, Understanding Fifth-Harmonic Generation in CLBO, Conference on Nonlinear Frequency Generation and Conversion - Materials and Devices XVII, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Patankar S, Yang ST, Moody JD, et al., 2017, Two-photon absorption measurements of deep UV transmissible materials at 213 nm, APPLIED OPTICS, Vol: 56, Pages: 8309-8312, ISSN: 1559-128X
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.
Ross JS, Higginson DP, Ryutov D, et al., 2017, Transition from Collisional to Collisionless Regimes in Interpenetrating Plasma Flows on the National Ignition Facility, PHYSICAL REVIEW LETTERS, Vol: 118, ISSN: 0031-9007
Huntington CM, Manuel MJ-E, Ross JS, et al., 2017, Magnetic field production via the Weibel instability in interpenetrating plasma flows, PHYSICS OF PLASMAS, Vol: 24, ISSN: 1070-664X
Goyon C, Pollock BB, Turnbull DP, et al., 2017, Ultrafast probing of magnetic field growth inside a laser-driven solenoid, PHYSICAL REVIEW E, Vol: 95, ISSN: 2470-0045
Clayson T, Suzuki-Vidal F, Lebedev SV, et 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.
Swadling GF, Ross JS, Manha D, et al., 2017, Initial experimental demonstration of the principles of a xenon gas shield designed to protect optical components from soft x-ray induced opacity (blanking) in high energy density experiments, PHYSICS OF PLASMAS, Vol: 24, ISSN: 1070-664X
Hare JD, Suttle L, Lebedev SV, et 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.
Swadling GF, Ross JS, Datte P, et al., 2016, Design calculations for a xenon plasma x-ray shield to protect the NIF optical Thomson scattering diagnostic, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 87, ISSN: 0034-6748
Ross JS, Datte P, Divol L, et al., 2016, Simulated performance of the optical Thomson scattering diagnostic designed for the National Ignition Facility, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 87, ISSN: 0034-6748
Datte PS, Ross JS, Froula DH, et al., 2016, The design of the optical Thomson scattering diagnostic for the National Ignition Facility, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 87, ISSN: 0034-6748
Suttle LG, Hare JD, Lebedev SV, et 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.
Swadling GF, Lebedev SV, Hall GN, et 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.
Haerendel G, Suttle L, Lebedev SV, et 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.
Galbraith J, Datte P, Ross S, et al., 2016, Design of an Optical Thomson Scattering Diagnostic at the National Ignition Facility, Conference on Target Diagnostics Physics and Engineering for Inertial Confinement Fusion V, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Datte P, Ross JS, Froula D, et al., 2016, The preliminary design of the optical Thomson scattering diagnostic for the National Ignition Facility, 9th International Conference on Inertial Fusion Sciences and Applications (IFSA), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Suzuki-Vidal F, Lebedev SV, Ciardi A, et al., 2015, BOW SHOCK FRAGMENTATION DRIVEN BY A THERMAL INSTABILITY IN LABORATORY ASTROPHYSICS EXPERIMENTS, Astrophysical Journal, Vol: 815, ISSN: 1538-4357
The role of radiative cooling during the evolution of a bow shock was studied in laboratory-astrophysics experiments that are scalable to bow shocks present in jets from young stellar objects. The laboratory bow shock is formed during the collision of two counterstreaming, supersonic plasma jets produced by an opposing pair of radial foil Z-pinches driven by the current pulse from the MAGPIE pulsed-power generator. The jets have different flow velocities in the laboratory frame, and the experiments are driven over many times the characteristic cooling timescale. The initially smooth bow shock rapidly develops small-scale nonuniformities over temporal and spatial scales that are consistent with a thermal instability triggered by strong radiative cooling in the shock. The growth of these perturbations eventually results in a global fragmentation of the bow shock front. The formation of a thermal instability is supported by analysis of the plasma cooling function calculated for the experimental conditions with the radiative packages ABAKO/RAPCAL.
Burdiak GC, Lebedev SV, Harvey-Thompson AJ, et al., 2015, Characterisation of the current switch mechanism in two-stage wire array Z-pinches, Physics of Plasmas, Vol: 22, ISSN: 1089-7674
In this paper, we describe the operation of a two-stage wire array z-pinch driven by the 1.4 MA,240 ns rise-time Magpie pulsed-power device at Imperial College London. In this setup, an inversewire array acts as a fast current switch, delivering a current pre-pulse into a cylindrical load wirearray, before rapidly switching the majority of the generator current into the load after a100–150 ns dwell time. A detailed analysis of the evolution of the load array during the pre-pulse ispresented. Measurements of the load resistivity and energy deposition suggest significant bulk heatingof the array mass occurs. The 5 kA pre-pulse delivers 0.8 J of energy to the load, leaving itin a mixed, predominantly liquid-vapour state. The main current switch occurs as the inverse arraybegins to explode and plasma expands into the load region. Electrical and imaging diagnostics indicatethat the main current switch may evolve in part as a plasma flow switch, driven by the expansionof a magnetic cavity and plasma bubble along the length of the load array. Analysis ofimplosion trajectories suggests that approximately 1 MA switches into the load in 100 ns, correspondingto a doubling of the generator dI/dt. Potential scaling of the device to higher currentmachines is discussed. V
Swadling GF, Hall GN, Lebedev SV, et al., 2015, Commissioning of a Rotated Wire Array Configuration for Improved Diagnostic Access, IEEE TRANSACTIONS ON PLASMA SCIENCE, Vol: 43, Pages: 2503-2508, ISSN: 0093-3813
Veloso F, Munoz-Cordovez G, Donoso-Tapia L, et al., 2015, Ablation dynamics in wire array Z-pinches under modifications on global magnetic field topology, Physics of Plasmas, Vol: 22, ISSN: 1089-7674
The dynamics of ablation streams and precursor plasma in cylindrical wire array Z-pinches under temporal variations of the global magnetic field topology is investigated through experiments and numerical simulations. The wire arrays in these experiments are modified by replacing a pair of consecutive wires with wires of a larger diameter. This modification leads to two separate effects, both of which impact the dynamics of the precursor plasma; firstly, current is unevenly distributed between the wires and secondly, the thicker wires take longer to fully ablate. The uneven distribution of current is evidenced in the experiments by the drift of the precursor off axis due to a variation in the global magnetic field topology which modifies the direction of the ablation streams tracking the precursor position. The variation of the global magnetic field due to the presence of thick wires is studied with three-dimensional magnetohydrodynamic (MHD) simulations, showing that the global field changes from the expected toroidal field to a temporally variable topology after breakages appear in the thin wires. This leads to an observed acceleration of the precursor column towards the region closer to the thick wires and later, when thick wires also present breakages, it continues moving away from the original array position as a complicated and disperse object subject to MHD instabilities.
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