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 be en observed while changing the heating location, the ECRH power, the plasma shape and the safety factor. For edge safety factors q(alpha) > 4.5, safet y factors on-axis q(0) < 1 and small plasmas, complete sawtooth stabilizati on 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 pro duced or suppressed are reported, and the origins for such tron-standard be haviour are discussed.