Observation of High-Field-Side Crash and Heat Transfer during Sawtooth Oscillation in Magnetically Confined Plasmas

High resolution (temporal and spatial), two-dimensional images of electron temperature fluctuations during sawtooth oscillations were employed to study the crash process and heat transfer in magnetically confined toroidal plasmas. The combination of kink and local pressure driven instabilities leads to a small poloidally localized puncture in the magnetic surface at both the low and the high field sides of the poloidal plane. This observation closely resembles the ``fingering event'' of the ballooning mode model with the high-$m$ mode only predicted at the low field side.