Spontaneous improvement of TJ-II plasmas confinement

Spontaneous improvements in particle and energy confinement have been observed in TJ-II plasmas with <iopmath latex="$\approx $">&approx;</iopmath>300 kW of electron cyclotron resonance heating. Density and temperature profiles broaden giving rise to energy content enhancement up to a factor of 1.4. The transport analysis on one of these discharges describes the evolution of the profiles via a sudden reduction (<iopmath latex="$\sim $">~</iopmath>50&percent;) of the thermal and particle diffusivities inside the main plasma. A brief comparison with transition phenomena in other devices is given.