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Title: Studies of plasmas produced by high power laser radiation
Author: Evans, A. M.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1988
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This thesis describes some studies of ion emission from a laser-produced plasma. The plasmas were produced by focussing a light pulse of wavelength 1.06 um and duration 35 ps from a multistage high power (GW) Neodymium-in-Glass laser system onto a solid plane target. An ion analyser mounted normal to the target, with its axis pointing directly at the site of the plasma, received a small fraction of the ions emitted from the plasma and provided data regarding their atomic nature and charge state. Preliminary measurements of ion emission using an oil-pumped vacuum chamber revealed that the targets were severely contaminated with an impurity of a hydrocarbon nature. Pre-cleaning of the target with a prior laser pulse was not possible since it was found that the impurity was rapidly re-deposited. The installation of a new turbomolecular pumping system and the meticulous cleaning of the vacuum chamber and plasma diagnostics alleviated these problems and allowed, for the first time, plasmas to be produced and studied that either contained or did not contain ions of a hydrocarbon impurity, depending upon the nature of the target site. The nature of the target site irradiated was either 'Fresh' or 'Cratered'; a fresh target site was an area of the target not previously irradiated with laser light whereas a cratered target site was an area previously irradiated with laser light. It soon became clear that plasmas produced in the new clean vacuum chamber from a 'cratered' target site contained ions of a much higher charge state than seen from a 'fresh' contaminated target site. This observation was further substantiated when the limited resolution of the original ion analyser was greatly increased by the use of an electromultiplier system of much wider bandwidth. The refinements made to the previous state of this project have made possible studies of a number of important features of the plasma, for example, fast ions where their true nature and charge state could be established. As a consequence it should be possible in the future to obtain satisfactory estimates of the electron temperature in the plasma corona.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available