Studying the impurity charge and main ion mass dependence of impurity confinement in ECR-heated TJ-II stellarator

• Published in: Plasma physics and controlled fusion Vol. 56; no. 12; pp. 124007 - 10
• Main Authors: Zurro, B, Hollmann, E M, Baciero, A, Ochando, M A, McCarthy, K J, Medina, F, Velasco, J L, Pastor, I, Baião, D, de la Cal, E, Rapisarda, D
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.12.2014
• Subjects: Arrays; blow-off injection; bolometer tomography; Charge; Confinement; Controlled fusion; Electric fields; Impurities; Isotope effect; plasma impurities; plasma transport; stellarator; Stellarators; TJ-II
• ISSN: 0741-3335; 1361-6587
• DOI: 10.1088/0741-3335/56/12/124007

The dependence of impurity confinement time on the charge and mass of the impurity ions injected from various samples (LiF, BN, W) by the laser blow-off method is reported for electron cyclotron heated discharges of the TJ-II heliac. Distinct impurity confinements are distinguished clearly for these injected ions in the plasma core as revealed by soft x-ray analysis and by tomographic reconstruction of bolometer array signals. A dependence of impurity confinement with charge seems to be the most probable explanation, as confirmed by the analysis of spectrally resolved data in the vacuum-ultraviolet range. This is discussed in terms of the dependence of impurity neoclassical transport on the background radial electric field. In addition, the impurity confinement of LiF is studied for a set of discharges in which the hydrogenic isotope mixture (H, D) is known (and evolves along the experiment), revealing a moderate isotope effect that is observed for the first time in particle confinement in a stellarator. This effect is consistent with a similar effect reported in global energy confinement time in the ATF stellarator.