Spontaneous improvement of TJ-II plasmas confinement

Spontaneous improvements in particle and energy confinement have been recently observed in some TJ-II plasmas. Their energy content increases up to a factor. The transport analysis indicates substantial (∼50%) reductions of the thermal and particle diffusivities around the region of steepest pressure gradients. For a series of ∼300 kW Electron Cyclotron Resonance Heating (ECRH) discharges in which a systematic reduction of the gas puffing rate has been carried out, the phenomenon is observed until the gas puffing rate is too low. Therefore, the gas puffing control and hence the fuelling rate on the discharge, seem to be critical in the achievement of the transition. The results here shown add to stellarator confinement phenomenology. Copyright (2002) Australian National University- Research School of Physical Sciences and Engineering