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Limit cycle oscillations measurements with Langmuir and ball-pen probes on COMPASS

This contribution presents the experimentally observed edge plasma evolution during limit cycle oscillations (LCO) measured with a new Langmuir and ball-pen multi-pin probe head at the COMPASS tokamak. The observed LCO regime modulates the intensity of density fluctuations , radial electric field Er and intensity of emission with a frequency 3–5 kHz. The density fluctuations grow after Er decreases in strength which appears to be strongly correlated with the evolution of the pressure gradient . The magnetic signature of the LCO shows a left–right asymmetry with propagation from the low to high field side. High-frequency (above 100 kHz) precursor-like oscillations are observed as well.