Tungsten nanostructure formation in a magnetron sputtering device



Petty, Thomas
(2015) Tungsten nanostructure formation in a magnetron sputtering device. Doctor of Philosophy thesis, University of Liverpool.

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Abstract

Fuzzy tungsten is a phenomena that could potentially occur in future fusion reactors. There are three conditions for fuzz to form, the existence of He ions impinging on a tungsten sample for a sufficient amount of time, that these ions be of sufficient energy, and that the surface temperature of the tungsten is hot enough. These conditions will likely be fulfilled in ITER, the future flagship fusion reactor. Therefore efforts to understand and characterise the fuzz formation are of importance. A thorough literature review has been provided, bringing together for the first time works from over 100 papers on the area. The history of its discovery is explained and the characteristics of the structure are detailed. The potential for fuzz to occur in ITER is shown, and positive and negative aspects of fuzz for fusion operation are discussed. The current accepted growth mechanisms are explained and a brief summary of the current work on simulating the phenomena is given. Fuzz appearing on other metals is introduced, and evidence of creating fuzz in a tokamak is shown. Methods for removing fuzz are presented should it be deemed necessary to do so in ITER. Results are compiled from many fuzz samples created in the literature spanning four orders of magnitude of fluence. This provided the foundation for a collaboration with the UC San Diego, and lab time at their facilities. Several samples were created to complement the dataset. The compilation provides new insights into the growth equation surrounding fuzz formation. A new addition to the equation is introduced in the form of an incubation fluence, a minimum fluence required before fuzz can develop. The growth model is expanded to fuzz grown in erosive regimes, and a new equation is proposed that encompasses the competition between growth and erosion, giving good predictions for the resulting equilibrium thickness. A new method for creating fuzz has been developed in a cheap and simple way. Conventional methods involve using large scale expensive devices, only available in a select few places worldwide. Magnetrons are apparent in many laboratories around the world and a technique for making fuzz in them has been developed. The three parameters controlling fuzz formation have been studied in the magnetron by making samples at many different conditions. The results provide new insight into early fuzz formation, providing results in a fluence range often over-looked. A cross-over fluence is noted from pre-fuzz to fully formed fuzz, overlapping with the predicted incubation fluence. The results differ slightly from fuzz created in other devices at similar fluence. The most probable cause is due to the unique existence of deposition of metallic particles in a magnetron incident on the samples during the growth of fuzz.

Item Type: Thesis (Doctor of Philosophy)
Subjects: Q Science > QC Physics
Divisions: Fac of Science & Engineering > School of Electrical Engineering, Electronics and Computer Science
Depositing User: Symplectic Admin
Date Deposited: 10 Nov 2015 08:53
Last Modified: 11 Aug 2016 14:42
URI: http://livrepository.liverpool.ac.uk/id/eprint/2036140
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