Ultra-fast Langmuir probe measurements in MAST-U edge plasma

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Langmuir probes are commonly used to measure plasma parameters such as electron temperature, ion saturation current and floating potential in fusion and technological plasmas. Conventional Langmuir probe systems, however, are not well suited for plasma turbulence investigations due to either a spatial or temporal resolution limitation. Experiments have shown that the edge region in a fusion plasma is very turbulent. For example, fast transient filamentary structures transport plasma particles and heat radially outward across the open magnetic field lines (scrape-off-layer). The midplane reciprocator, fitted with several electrodes at the probe head, is a key diagnostic for measuring filament properties in the scrape-off-layer.A novel ultra-fast Langmuir probe system, based on a field programmable gate array (FPGA), is currently being developed through a collaboration between UKAEA, University of Liverpool and MIT and is due to end in March 2023. This is expected to provide real-time outputs (-1 MHz temporal resolution) of all three plasma parameters using a single electrode. This proposed, primarily experimental, project will continue the development of this system and will use the diagnostic to investigate fast transport phenomena in the edge plasma region of the MAST-U spherical tokamak.