Application of x-ray diagnostics to the characterisation of pulsed power driven magnetic reconnection experiments

Abstract

This thesis describes results obtained using a versatile, pulsed power driven platform for magnetic reconnection experiments. The platform used the MAGPIE generator (1.4 MA, 240 ns) to produce plasma inflows (Vin ≈ 50 km s−1) that carry a strong azimuthal magnetic field (Bin 3 T) and persisted for many hydrodynamic timescales. The platform consisted of a pair of inverse (or exploding) wire arrays, and the plasma flows were generated by the ablation of material from these arrays. Plasma conditions were diagnosed with an existing suite of high spatial and temporal resolution laser probing diagnostics including laser interferometry, Thomson scattering, and Faraday rotation imaging. These results indicated that the plasma flows from the two arrays carried oppositely directed magnetic fields and that, in the region where the two flows met, magnetic flux was efficiently annihilated in a well defined reconnection layer. The magnetic energy released in the flux annihilation process was observed to cause plasma heating, and to increase fluid velocity in the outflows. The reconnection layer was observed to be unstable to the plasmoid instability. Preliminary evidence indicated that the reconnecting plasma generated a population of fast electrons. In order to investigate this possibility in more detail, a variety of X-Ray diagnostics were used to characterise experimental conditions. These included spherically bent crystal X-Ray spectroscopy; time integrated, filtered pinhole imaging; and time resolved, filtered slit imaging. The results obtained using X-Ray diagnostics were consistent with the previous laser probing measurements, but do not conclusively prove that particle acceleration occurred in the experiments