Speaker
Description
Outside the separatrix lies the scrape-off layer (SOL), within which the heat and particle flux from the core flows to the target; for which future devices may be in excess of $20\,\mathrm{MWm}^{-2}$. To mitigate such fluxes, a deeper understanding of transport in the SOL is vital. SOL transport is dominated by turbulent processes across a broad spectrum of time and spatial scales. For a deeper examination, a coalition of diagnostics are required to cover these domains. This collection of diagnostics span a variety of plasma parameters that may be used in conjunction to aid in verification of the edge turbulence models GRILLIX and GENE-X. However, many diagnostics have relatively narrow spatial and frequency ranges, with multiple overlaps, and few cover both high frequencies and large spatial regions.
Langmuir probes have long been used for edge plasma measurements, however, their effectiveness is limited to the voltage range and frequency the probe is swept. The $IV$ characteristics determined from the probe contain the electron density, floating potential, and electron temperature. However, plasma properties vary radially from the far SOL to the separatrix. This change in properties may lie outside of the chosen voltage range, reducing the accuracy and effectiveness of the swept probe. Currently, fast fluctuations are missed by swept probes due to limitations of sweeping the entire voltage range.
An FPGA based, digital Mirror Langmuir Probe dynamically adjusts the probe bias potential in response to measured plasma parameters. This diagnostic is capable of ultra-fast sweeping, allowing high time resolution for direct plasma parameter measurements in the SOL. Combined with the spatial range of the midplane manipulator system on AUG, complimentary measurements can be made with the existing cohort of diagnostics. High frequency probe measurements provide increased time resolution inside filament structures, the dominant turbulent transport mechanism in the SOL, revealing further detail.
This contribution focuses on producing such a diagnostic, multiple testing stages, and incorporation of the FPGA within the manipulator system. Some initial test results of the FPGA will be presented, followed by an outlook of the future of the project, including possible exploitations of the implemented diagnostic.