The Role of Flux Advection in the Development of the Ablation Streams and Precursors of Wire Array Z-pinches

Greenly, J. B.; Martin, Matthew; Blesener, I. C.; Chalenski, D.A.; Knapp, Patrick; McBride, R. D.

doi:10.1063/1.3079752

Cited by 32 publications

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“…The ablated plasma is accelerated to velocity of $1 Â 10 7 cm/s in the close vicinity of the wires (inside the first $1-2 mm), and then propagates with almost constant velocity. The plasma flow is expected to possess a frozen-in magnetic field, the advection of the magnetic field having been observed previously in standard wire arrays, [13][14][15] although not measured for inverse arrays prior to these experiments. The wire arrays used here consist of 16 Al wires, each 40 lm in diameter and 15 mm in length, and positioned on a diameter of 20 mm coaxially with the central (8 mm diameter) electrode (Figs.…”

Section: Experimental Setup and Diagnosticsmentioning

confidence: 86%

The formation of reverse shocks in magnetized high energy density supersonic plasma flows

et al. 2014

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

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Section: Experimental Setup and Diagnosticsmentioning

confidence: 86%

The formation of reverse shocks in magnetized high energy density supersonic plasma flows

et al. 2014

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“…1(a). Ablation flows form in a similar manner to those produced by standard ("imploding") wire arrays [16][17][18]; however, here the J × B force acts to direct the plasma radially outwards, into a region initially free of magnetic fields. The ablated plasma is accelerated away from the wires, reaching a velocity of ∼50 km=s within the first 1-2 mm, and thereafter propagates with an almost constant velocity.…”

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confidence: 99%

Structure of a Magnetic Flux Annihilation Layer Formed by the Collision of Supersonic, Magnetized Plasma Flows

et al. 2016

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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 (T i ∼ZT e , with average ionizationZ ¼ 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. DOI: 10.1103/PhysRevLett.116.225001 The interaction of supersonic, counterstreaming plasma flows occurs in many astrophysical scenarios (e.g., astrophysical jets [1] and termination shocks [2,3]) and in laboratory experiments (e.g., colliding plasmas in inertial confinement fusion hohlraums [4]). The presence of frozenin magnetic fields advected by the colliding flows could play an important role in determining the structure of the interaction region in these systems. Collisions of magnetized plasmas with oppositely directed magnetic fields should eventually lead to annihilation of the flux via magnetic reconnection. In many astrophysical scenarios reconnection occurs in high beta plasmas and is strongly driven, with ram pressure significantly exceeding the magnetic pressure. The structure of the reconnection layer in these conditions is unknown, but is expected to adjust to accommodate the rate of magnetic flux delivered into the layer, where, for example, a pileup of the magnetic flux could contribute to controlling the reconnection rate [5,6]. A number of recent laser-driven, high energy density physics (HEDP) experiments [7][8][9][10] have investigated magnetic reconnection in the strongly driven regime, as well as the formation of astrophysically relevant collisionless shocks [11] and self-organized field structures [12]. Large-scale field structures produced by collisions between laser-driven plasma flows have, for example, been interpreted [11] as being due to the accumulation of advected toroidal magnetic fields generated via the Biermann battery mechanism at the laser spots [13]. Despite the importance of magnetic fields in defining the properties of shocks formed in HEDP plasmas, experimental information is still limited.In this Letter we present experimental data characterizing the structure of an interaction layer formed by the collision of two counterstreaming, supersonic (sonic Mach number M S > 3), magnetized plasma flows. These flows advect embedded magnetic fields (magnetic Reynolds number Re M > 30), orientated in opposing directions perpendicular to the flow, and their interaction is strongly driven [i.e., high dynamic beta regime,. The experiments provide detaile...

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“…Initially the individual wires are surrounded by closed magnetic field lines, but as the plasma accelerates outwards it carries with it some fraction of the drive current. This current causes a reconfiguration of the overall magnetic topology 18,19 that results in a global azimuthal magnetic structure. The coronal plasma is continuously replenished by ablation from the surface of cold wire cores and this plasma is continuously accelerated outwards for the duration of the current pulse, resulting in long lasting, magnetised plasma flows.…”

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confidence: 99%

Formation and structure of a current sheet in pulsed-power driven magnetic reconnection experiments

et al. 2017

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

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The Role of Flux Advection in the Development of the Ablation Streams and Precursors of Wire Array Z-pinches

Cited by 32 publications

References 0 publications

The formation of reverse shocks in magnetized high energy density supersonic plasma flows

The formation of reverse shocks in magnetized high energy density supersonic plasma flows

Structure of a Magnetic Flux Annihilation Layer Formed by the Collision of Supersonic, Magnetized Plasma Flows

Formation and structure of a current sheet in pulsed-power driven magnetic reconnection experiments

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