Optical characterisation of a low temperature plasma jet

Low temperature plasma jets are of particular interest due to their unique way of producing reactive species even at room temperature and atmospheric pressure. They therefore have the potential to be used for various applications, in plasma medicine and surface modification in particular. The characterisation of these plasma jets is important in order to be able to control them for the desired application.<br/><br/>Various optical diagnostics have been implemented to establish the formation and propagation of the plasma, as well as to estimate the important parameters such as electron density, <i>n_e</i> , and electron temperature, <i>T_e</i>. Initially imaging on nanosecond timescale established that the plasma, although continuous to the naked eye, consisted of plasma bullets travelling at velocities of up to 10⁵ m s⁻¹. 2D quasi monchromatic images of the plasma, obtained by isolating the light produced by individual spectral transitions, allowed an estimation of the density of excited helium states within the plasma, in the region of 1 × 10⁹ − 2 × 10¹⁰ cm⁻³.<br/><br/>Optical emission spectroscopy was used to identify the species present, to estimate the electron temperature of the plasma using helium line ratios, and to estimate the gas temperature using nitrogen emission. The electron temperature and gas temperature were found to be 0.3 eV and 303 K respectively, which confirmed that the plasma jet was operating in the low temperature regime. Emission from allowed and forbidden helium lines was also utilised, in this case to estimate the electric field present, which was calculated to be 32.1 kV cm⁻¹.<br/><br/>Thomson scattering was also attempted in an effort to obtain electron density and temperature estimates. However, the electron density of the plasma in question was simply too low to detect using the experimental set-up at hand. However, using a model consisting of data from Raman scattering it was possible to put an upper limit on the electron density of the plasma of 9.95 × 10¹² cm⁻³.<br/>

Name dc:type.qualificationname

Doctor of Philosophy

Level dc:type.qualificationlevel

Doctoral Thesis

Grantor dc:publisher.institution

Queen's University Belfast

Year dc:date.issued

2020

Author dc:creator

• Irwin, Rachael

Advisor dc:contributor.advisor

• Riley, David

Language dc:language

eng

Identifier

oai:pure.qub.ac.uk/portal:studenttheses/d1bf225a-d2ff-49aa-988e-13d9f4c0be55

OAI identifier oai:identifier

oai:pure.qub.ac.uk/portal:studenttheses/d1bf225a-d2ff-49aa-988e-13d9f4c0be55