Application of x-ray diagnostics to the characterisation of pulsed power driven magnetic reconnection experiments
File(s)
Author(s)
Halliday, Jonathan
Type
Thesis
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
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
Version
Open Access
Date Issued
2020-05
Date Awarded
2021-11
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Lebedev, Sergey
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)