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 delta n(e), radial electric field E-r and intensity of D-alpha emission with a frequency 3-5 kHz. The density fluctuations grow after E-r decreases in strength which appears to be strongly correlated with the evolution of the pressure gradient partial derivative(r)p. 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.