Transport in threshold plasmas for a confinement transition in the TJ-II stellarator

A description and transport analysis (energy and particles) of neutral beam heated plasmas is shown for two almost identical magnetic configurations except for a ≈1% difference in their rotational transform, t. Due to the low magnetic shear of TJ-II magnetic fields, such difference takes the low order rational t = 8/5 to the plasma edge in one of them, while in the other the 8/5 value is near the edge but inside the plasma. A transport transition happens at lower density and plasma energy for the configuration that includes the t = 8/5, which exhibits better particle confinement already before the transition. (paper)