The dynamics of the formation of the edge particle transport barrier at TJ-II

摘要

A large set of discharges with both spontaneous and forced confinement transitions at low electron density is studied at the stellarator TJ-II in different magnetic configurations. By means of a Bayesian technique, using refiectometry and interferometry, electron density profiles are reconstructed in the outer half of the plasma. A scanning heavy ion beam probe delivers information on the global evolution of the plasma potential. Langmuir probes are used to measure long-range correlations. Together, a comprehensive picture is obtained of the evolution of various key global plasma profiles and parameters across forward and backward transitions associated with the formation of an edge sheared flow layer. The impact of low-order rationals on the transition is elucidated.