IMPURITY TRANSPORT MEASUREMENTS OF BIASED H-MODE IN HYDROGEN AND DEUTERIUM PLASMAS ON THE PHAEDRUS-T TOKAMAK

Soft X-ray spectroscopy was used to study the transport of the dominat ing impurity, carbon, in the central region of the Phaedrus-T tokamak in ohmic and high confinement mode (H mode) plasmas. These H modes wer e induced by an electrode positioned in the edge of the plasma and bia sed positive with respect to the Limiter. The primary source of carbon in the Phaedrus-T tokamak mak plasma is the graphite limiter. A soft X ray polychromator utilizing multilayer mirrors (MLM) as dispersive e lements simultaneously monitored the Lyman alpha emission of H-I-like carbon at 33.7 Angstrom, and the blended singlet and triplet transitio ns of He-I-like carbon at 40.3 and 40.7 Angstrom, respectively, and sp atially resolved their distributions in the plasma with a temporal res olution of 1 ms. The measured impurity emission profiles from the ohmi c and H mode portions of hydrogen and deuterium plasmas were analysed with the Multiple Ionization State Transport (MIST) code in order to e stimate the impurity transport in the plasma. Large increases in the i mpurity particle cofinement time were observed as the plasma made the transition from ohmic to H mode, and the improvement in the impurity c onfinement was found to be greater in the deuterium plasmas. Compariso ns were made between the emission profiles, which are used to probe th e effects of the H mode deep inside the plasma, and the I-V characteri stics of the biased electrode, which are used to monitor the edge of t he plasma. The I-V characteristics of the biased. electrode were found to have a direct impact on the carbon emission profiles.