An experimental platform for pulsed-power driven magnetic reconnection

Abstract

We describe a versatile pulsed-power driven platform for magnetic reconnection experiments, based on exploding wire arrays driven in parallel [Suttle, L. G. et al. PRL, 116, 225001]. 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 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 which 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. arXiv:1711.06534v2 [physics.plasm-ph]

Interactions of magnetized plasma flows in pulsed-power driven experiments

“…In carbon experiments however, the larger electron temperature of 60 eV results in a Lundquist number of S~100, which is sufficiently large that it is expected to place the layer in the plasmoid unstable, semi-collisional reconnection regime[41,42]. This is consistent with observations of the layer structure, which show the formation of plasmoids in both self-emission images [figure 3(b)] and laser interferometry[25,31,33]. Measurements with B-dot probes placed in the exhaust of the layer have indicated these indeed possess a magnetic O-point structure[25,31].…”

“…Magnetic reconnection is a complex and multifaceted process which is an active topic of research across space, astrophysics and plasma physics [28,29]. One of the most notable applications of the inverse wire array setup therefore has been to create a platform for studying this process in the laboratory [25,[30][31][32][33]. In these experiments two identical inverse wire arrays are fielded side-by-side on the MAGPIE generator, connected in parallel and in the same polarity to each receive a 50% share of the current supply.…”

Exploring astrophysics-relevant magnetohydrodynamics with pulsed-power laboratory facilities

“…50) and in multi-frame self-emission images (Hare et al, 2017a). Measurements with miniature magnetic probes (Hare et al, 2018) also indicate the presence of an O-point magnetic field structure as expected in a plasmoid. It is interesting to note that plasmoids in these experiments were observed at a relatively small Lundquist number of S~100.…”

“…Characteristic plasma parameters in the magnetic reconnection layer. [Suttle et al, 2018;Hare et al, 2018 The formation of the reconnection layer in Al and C plasmas has many features which are common for both materials: the layer thickness is comparable to the ion skin depth (/d i ~1); the incoming plasma flows are re-directed and accelerated in the ydirection to velocities V y > V A ; the plasma is strongly heated, and the ion temperature significantly exceeds both the electron temperature (T i ~ ZT e , with Z=6-7) and the kinetic energy of the incoming ions. Measurements show that the conversion of the magnetic energy provides a significant contribution to the overall energy balance, ~50% for Carbon (Hare et al, 2017a).…”

Use of synchrotron-based radiography to diagnose pulsed power driven wire explosion experiments

“…Pulsed power is often used to drive high energy density physics (HEDP) experiments, exploring topics including laboratory astrophysics, 1,2 high pressure materials, 3 and inertial confinement fusion experiments. 4,5 Perhaps the simplest experiment of this kind involves the explosion of a single thin metal wire either in a vacuum or in a medium such as water.…”