Behaviour of central plasma relaxation oscillations during localized electron cyclotron heating on the TCV tokamak

During initial studies of ECRH in the TCV tokamak, non-standard central MHD activities, such as humpbacks and saturated and inverted sawteeth, have been observed while changing the heating location, the ECRH power, the plasma shape and the safety factor. For edge safety factors qa > 4.5, safety factors on-axis q(0) < 1 and small plasmas, complete sawtooth stabilization was achieved with the present 1 MW gyrotron power, and it is likely that sawtooth stabilization can be achieved for all conditions at higher ECRH power. The conditions under which the various relaxation activities are produced or suppressed are reported, and the origins for such non-standard behaviour are discussed.