Diagnostic Development of Gas Delivery and Viewing System for Analysing the Electric Field Stark Effect on H-Alpha Light Emissions close to a Plasma Excitation Antenna
Creators: name: Frost, Benjamin
Publisher: name: The Australian National University
Year: 2020

description: Fusion - the process that powers the sun - offers the possibility of a clean and abundant source of energy in a world where alternatives rely on dwindling resources or struggle to generate reliable base load power. On earth, attaining fusion requires magnetic confinement of hydrogen plasma (the fourth state of matter) heated to many millions of degrees. Advanced diagnostic tools are used by scientists to probe and understand the physics of such magnetically confined high temperature plasmas. This project describes the development of a gas injection and associated optical spectroscopic imaging system for study of radio frequency electric fields in the sheath of an unshielded fast wave heating antenna on the H-1NF plasma confinement facility at the Australian National University. It is proposed that measurements of the Stark splitting and polarization of Balmer-alpha light emissions emanating from a supersonic hydrogen gas beam injected into the plasma volume directly under the antenna system could be used to give information about the sheath field and a better understanding of near field ion heating effects. The primary work of this thesis concerns the development and testing of the gas delivery system and the positioning and validation of the related viewing apparatus. The gas injection system was designed for high speed short gas bursts with limited fluences in order minimize the perturbation on the plasma. It was also developed with a view to reducing the spread of the injected beam as much as possible by tailoring the geometric characteristic of the nozzle. To test theoretical expectations related to nozzle design a method for characterising the gas beam was developed that involved a sweeping orientation-tracked anemometer system installed in a vacuum test tank. The nozzle characterisation results showed that the delivered flow rates were consistent with theory and that the directionality and localization of the beam was an improvement upon previous nozzles implemented on H-1NF. The plenum/nozzle system was installed at a location above the heating antenna and plumbed out to a gas hub allowing access to a variety of different gases. A control system for administering, managing and acquiring data for the injector was also developed and was interfaced with the H-1NF control and timing system. The beam imaging requirements were ascertained and optimized using CAD models of H-1NF. Experimental images captured by the camera conformed well to modelling expectations - a clear view of the plasma volume of interest under and around the antenna was obtained. Images were obtained for a number of gases injected into various plasma configurations. The illumination of an electron beam produced by an electron gun inserted in the closed magnetic volume could be used to confirm the viewing geometry. The scope of this thesis work did not include spectroscopic or polarization-based imaging. For appropriate injection conditions, it should be noted that the puffer could also be utilized as a gas fuelling device.