Importance of the Rotational Transform for L¿H Transitions in the TJ-II Stellarator

We study the effect of the rotational transform profile on the L¿H confinement transitions in the neutral beam-heated plasmas in the TJ-II stellarator. The rotational transform profile in the vacuum is determined by the external coil currents but is modified by the plasma current, (Formula presented.). We find that L¿H confinement transitions systematically occur when the configuration and plasma current are such that a low-order rational is placed in the plasma edge region, with a distribution centered around (Formula presented.). It is suggested that magnetohydrodynamic turbulence plays an important role in triggering the L¿H transitions at TJ-II.

confinement transitions; magnetic confinement; rational surfaces; rotational transform; stellarator; turbulence

Importance of the Rotational Transform for L¿H Transitions in the TJ-II Stellarator Articles