High energy density magnetic reconnection experiments in colliding carbon plasma flows

• Main Author: Hare, Jack Davies
• Other Authors: Lebedev, Sergey
• Published: Imperial College London 2017
• Subjects: 621.044
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.721591

This thesis presents a detailed study of magnetic reconnection in a quasi-two-dimensional pulsed-power driven laboratory experiment. These experiments were performed at the 1.4 MA, 240 ns rise time Magpie facility at Imperial College London. Initial experiments are presented which demonstrate the viability of carbon as a wire material, and the use of exploding wire arrays as a platform for laboratory astrophysics. In the reconnection experiments, two exploding carbon wire arrays are placed side-by-side and driven in parallel by the Magpie current pulse. The carbon wires become plasma, creating super-sonic, sub-Alfvénic flows which advect anti-parallel magnetic fields towards the mid-plane between the two arrays, where the fields mutually annihilate inside a thin current sheet. A suite of temporally and spatially resolved diagnostics are used to study the reconnection process, including optical fast-framing, laser interferometry, Faraday Rotation imaging and Thomson Scattering. These detailed measurements allow the structure and dynamics of the reconnection layer to be determined, along with the nature of the inflows and outflows and the detailed energy partition during the reconnection process. The layer is unstable, exhibiting the repeated formation and ejection of plasmoids which have an associated magnetic structure measured by magnetic probes. The number and growth rate of these plasmoids agrees well with the predictions of semi-collisional tearing instability theory, and represent the first experimental observation of plasmoids in this regime. High electron and ion temperatures are observed, far in excess of what can be attributed to classical (Spitzer--Braginskii) resistivity or viscosity. Some possible anomalous heating mechanisms are discussed, including kinetic turbulence, and the plasmoid instability. Preliminary measurements of the out-of-plane velocity and magnetic field are presented along with the outlook for future experiments.