Experimental Study of Plasma Implosion Dynamics in a Two-Stage Wire Array Z-Pinch Configuration
Author(s)
Khoory, Essa
Type
Thesis
Abstract
This thesis presents results from experiments of a two-stage wire array Z-pinch
configuration carried out on the MAGPIE generator ( ~ 1.4MA in ~ 250ns) at
Imperial College, London. This configuration preconditions the load wires (heating
and expanding wires into columns of gas) before allowing the full current to
rapidly switch into the load. The preconditioning effect of cylindrical Al wire array
loads of different wire numbers and wire thicknesses were investigated from density
analysis of laser interferometry. It was found that thicker wires expand to larger
diameters than thinner wires in the preconditioning phase. The 30μm wire
expanded to a diameter of 3.7±0.4mm while the 10μm wire expanded to a
diameter of 1.6±0.4mm in ~ 170ns after current start.
Experiments were also conducted on a single Al wire load of different thicknesses.
Again thicker wires expanded to a larger diameter. This uniform column of Al gas
on axis showed a high degree of azimuthal symmetry. The fast current switch into
the load drives a snowplough implosion with an implosion time of ~ 25-30ns with
no apparent development of Rayleigh-Taylor instability. It was observed at
stagnation that the expansion the m=1 MHD instability into a helical structure
was responsible for the main X-ray pulse.
A cylindrical plasma ‘shell’ was formed by preconditioning an array of large wire
number and a small inter-wire separation causing the expanding wires to merge
before the current switch time. The shell imploded in a 0D manner with no
ablation phase and no trailing mass left behind as in standards wire arrays.
Implosion of the ‘shell’ was susceptible to R-T instability. Analysis of this
instability growth estimated an initial effective perturbation of ~ 1-2μm on the
preconditioned wires surface prior to implosion.
configuration carried out on the MAGPIE generator ( ~ 1.4MA in ~ 250ns) at
Imperial College, London. This configuration preconditions the load wires (heating
and expanding wires into columns of gas) before allowing the full current to
rapidly switch into the load. The preconditioning effect of cylindrical Al wire array
loads of different wire numbers and wire thicknesses were investigated from density
analysis of laser interferometry. It was found that thicker wires expand to larger
diameters than thinner wires in the preconditioning phase. The 30μm wire
expanded to a diameter of 3.7±0.4mm while the 10μm wire expanded to a
diameter of 1.6±0.4mm in ~ 170ns after current start.
Experiments were also conducted on a single Al wire load of different thicknesses.
Again thicker wires expanded to a larger diameter. This uniform column of Al gas
on axis showed a high degree of azimuthal symmetry. The fast current switch into
the load drives a snowplough implosion with an implosion time of ~ 25-30ns with
no apparent development of Rayleigh-Taylor instability. It was observed at
stagnation that the expansion the m=1 MHD instability into a helical structure
was responsible for the main X-ray pulse.
A cylindrical plasma ‘shell’ was formed by preconditioning an array of large wire
number and a small inter-wire separation causing the expanding wires to merge
before the current switch time. The shell imploded in a 0D manner with no
ablation phase and no trailing mass left behind as in standards wire arrays.
Implosion of the ‘shell’ was susceptible to R-T instability. Analysis of this
instability growth estimated an initial effective perturbation of ~ 1-2μm on the
preconditioned wires surface prior to implosion.
Version
Open Access
Date Issued
2013-06
Date Awarded
2013-10
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Lebedev, Sergey
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)