Leiden University Scholarly Publications

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Kooij, V.L. (2021)

Laser-generated toroidal helium plasmas

Doctoral Thesis
This dissertation is an experimental study of laser-generated, atmospheric pressure, transient toroidal helium plasmas.

The formation mechanism of these toroidal plasmas is identified and an estimate of their main plasma parameters is obtained. Furthermore, preliminary experiments are presented, aimed at heating these plasmas by absorption of microwave radiation, in order to counteract their transient nature.

Through a tomographic reconstruction, cross-sectional images of the toroidal plasma are obtained, visualising the fluid flow responsible for the generation of the toroidal structure. The origin of the flow is traced back to the structure of the plasma kernel. The shocks generated by this kernel interact akin to a Mach reflection and generate a low pressure region whose replenishment transforms the plasma into a toroid. Schlieren imaging, complemented with a novel scanning-probe technique, and thermodynamic modelling, as well as deliberately breaking the flow...Show moreThis dissertation is an experimental study of laser-generated, atmospheric pressure, transient toroidal helium plasmas.

The formation mechanism of these toroidal plasmas is identified and an estimate of their main plasma parameters is obtained. Furthermore, preliminary experiments are presented, aimed at heating these plasmas by absorption of microwave radiation, in order to counteract their transient nature.

Through a tomographic reconstruction, cross-sectional images of the toroidal plasma are obtained, visualising the fluid flow responsible for the generation of the toroidal structure. The origin of the flow is traced back to the structure of the plasma kernel. The shocks generated by this kernel interact akin to a Mach reflection and generate a low pressure region whose replenishment transforms the plasma into a toroid. Schlieren imaging, complemented with a novel scanning-probe technique, and thermodynamic modelling, as well as deliberately breaking the flow symmetry, confirm the formation mechanism. A high-power, sub-microsecond rise time, pulsed magnetron source has been designed for the microwave heating experiments. Its detailed design and the effect of the microwave pulse on the plasma are discussed.

This work is part of a larger study on self-organising knotted magnetic structures in plasma, which may find their application in nuclear fusion and astrophysical research.
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Tomography
Fluid flow
Plasma kernel
Shock wave
Mach reflection
Schlieren
Magnetron
Microwave heating
Self-organization
Laser-induced breakdown plasma
All authors
Kooij, V.L.
Supervisor
Bouwmeester, D.
Co-supervisor
Dood, M.J.A. de
Committee
Bruggeman, P.J.; Bongers, W.A.; Eliel, E.R.; Exter, M.P. van
Qualification
Doctor (dr.)
Awarding Institution
Leiden Institute of Physics (LION), Faculty of Science, Leiden University
Date
2021-04-28
Title of host publication
Casimir PhD Series
ISBN (print)
9789085934677

Publication Series

Name
2021-01