Impurity transport measurements of biased H mode in hydrogen and deuterium plasmas on the Phaedrus-T tokamak

Abstract

Soft X-ray spectroscopy was used to study the transport of the dominating impurity, carbon, in the central region of the Phaedrus-T tokamak in ohmic and high confinement mode (H mode) plasmas. These H modes were induced by an electrode positioned in the edge of the plasma and biased positive with respect to the limiter. The primary source of carbon in the Phaedrus-T tokamak plasma is the graphite limiter. A soft X-ray polychromator utilizing multilayer mirrors (MLM) as dispersive elements simultaneously monitored the Lyman alpha emission of H-I-like carbon at 33.7 AA, and the blended singlet and triplet transitions of He-I-like carbon at 40.3 and 40.7 AA, respectively, and spatially resolved their distributions in the plasma with a temporal resolution of 1 ms. The measured impurity emission profiles from the ohmic and H mode portions of hydrogen and deuterium plasmas were analysed with the Multiple Ionization State Transport (MIST) code in order to estimate the impurity transport in the plasma. Large increases in the impurity particle confinement time were observed as the plasma made the transition from ohmic to H mode, and the improvement in the impurity confinement was found to be greater in the deuterium plasmas. Comparisons were made between the emission profiles, which are used to probe the effects of the H mode deep inside the plasma, and the I-V characteristics of the biased electrode, which are used to monitor the edge of the plasma. The I-V characteristics of the biased electrode were found to have a direct impact on the carbon emission profiles