Interaction between a low-frequency electrostatic mode and resonant magnetic perturbations in MAST

A strong ?10?kHz mode is detected in both potential and density fluctuations of the edge plasma of the MAST tokamak using a reciprocating probe. The mode is radially localized, with outer limit ?2?cm inside the separatrix, and is affected on application of resonant magnetic perturbations generated by external coils. A shift in frequency with plasma rotation is found, and a rapid suppression of the mode is observed when it can couple to the imposed n?=?3 magnetic perturbations in the rotating frame. Non-linear coupling to high wave number turbulence is evident, and an increase in power of turbulence fluctuations is seen after suppression. These observations are then interpreted in the context of known low-frequency plasma modes present in the toroidal configuration. A possibility that the observed mode is a geodesic acoustic mode is considered and motivated by observations.