Global Energy Confinement Studies in TJ-II NBI Plasmas

This paper is an extension of global plasma confinement in electron-cyclotron operation to neutral beam heated plasmas in TJ-II. The reported NBI plasmas have been obtained under lithium-coated wall conditions. The plasma operation exhibits a substantially better density control and improved confinement as compared to similar boron-coated wall discharges heated by NBI. Regression analyses of energy confinement time yield a scaling law indicating degradation with power with an exponent of αP = 0.8. The scaling shows an improvement with density with exponent αn = 0.5. The dependencies on plasma radius and rotational transform have not been resolved so far because the –still incomplete– NBI database suffers from a high correlation between these two parameters (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)