Design and fabrication of conventional and non-conventional emissive probes for plasma diagnostics

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Plasma physics importance has increased over the last decades given the relatively new industrial and technological applications that involve this state of matter. For a proper performance and understanding of these applications, experimental techniques are required to determine plasma properties and to verify current main theories. This project aims to use current idealized main theories in plasma diagnostics to develop emissive probes that are able to take proper experimental measurements of plasma potential. The first part of the thesis will develop an idealized description of the interaction between probes and plasmas. Non idealizations will be defined given the disturbance caused by a probe presence inside a plasma region. Following the plasma-probe system, the Floating Point Method accuracy will be discussed regarding experimental plasma diagnostics. This method will be established as a convenient enough approximation to measure experimental plasma bias. A material study will be performed in order to define and propose non-conventional low work function materials such as LaB6, CeB6 and C12A7 : e- for thermionic applications. Both thoriated tungsten conventional probes and low work function non-conventional probes will be discussed. Due to the di culty to machine boride emissive tips during the project time-frame, non-conventional emissive probe designs and manufacturing process will be proposed for future projects. After the chosen design for conventional probes, their thermal model will be performed, dealing with the importance of the emitted electron current on the energy balance at high temperatures. These models will show the approximate power range at which the actual devices need to be operated to be in the saturated oating point region. Finally, the manufactured probes will be used to acquired experimental data. The results will seem to agree with the expected oating point behavior at high temperatures, where it is is extended to saturate. Measured potential deviations dependent on probe filament radius will be regarded.
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