Doherty, Columb (2018) Effect of target geometry on ion distributions from laser-produced colliding plasma stagnation layers. Master of Science thesis, Dublin City University.
Abstract
When a laser pulse of sufficient intensity is focussed onto a flat metal target it vaporises the surface, forming a high temperature and high-density plasma that rapidly expands in a direction perpendicular to the target. If two laser-produced plasmas are created in close proximity to each other, upon expansion they collide and may, depending on density and relative velocity, either interpenetrate or stagnate along the collision front.
The purpose of this work is to investigate the ion emission characteristics of stagnation layers with a view towards developing a potential ion beam source for other research and commercial uses. This research aims to shed new light on the control that can be exercised over laser plasma generated ions, specifically with the use of colliding plasmas, and to explore how one can selectively alter the kinetic energy and charge state densities of the emitted ion beams.
This was investigated using mass spectrometry, with a particular focus on how the target geometry affects generation and distribution of highly charged ions over a range of kinetic energies. The work was carried out using an ESA-ToF MS (Energy Sector Analyser-Time of Flight Mass Spectrometer) device designed and built with assistance from the Laser and Plasma Applications Group in Trinity College Dublin. This detector was ultimately capable of isotope resolution for Cu ions with a minimum of background noise and could be tuned to examine kinetic energies of positively or negatively charged plasma species.
Using a colliding plasma system comprising two point plasmas focussed on a flat target, and a series of wedge shaped targets with angles of 90°, 60° and 30°, the ion emission was measured over a range of kinetic energies for each target. The results consistently show a visible increase in the proportion of highly ionised Cu atoms produced by using narrower wedge targets for every pass energy examined. On average there is a three- fold increase in the number density of higher charged states (Cu3+,4+,5+) visible in the signal from a 90° target vs a 180° (flat) target. Concomitantly, there is a similar but smaller decrease in the percentage of lowly charged states in the 90° target signal.
Metadata
Item Type: | Thesis (Master of Science) |
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Date of Award: | November 2018 |
Refereed: | No |
Supervisor(s): | Costello, John T. |
Subjects: | Physical Sciences > Detectors Physical Sciences > Laser plasmas Physical Sciences > Lasers Physical Sciences > Physics Physical Sciences > Spectrum analysis Physical Sciences > Plasmas |
DCU Faculties and Centres: | DCU Faculties and Schools > Faculty of Science and Health > School of Physical Sciences Research Initiatives and Centres > National Centre for Plasma Science and Technology (NCPST) |
Use License: | This item is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 License. View License |
Funders: | Science Foundation Ireland |
ID Code: | 22636 |
Deposited On: | 21 Nov 2018 13:45 by John Costello . Last Modified 13 Dec 2019 13:58 |
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