TTF 05

1. DENSITY AND TEMPERATURE FLUCTUATIONS IN PEAKED DENSITY PROFILES ON ALCATOR C-MOD (3.5MB pdf) - A.G. Lynn, P. Phillips, W. Rowan, M. Sampsell N. Basse, B. Bose, E.M. Edlund, C. Fiore, A. Hubbard, L. Lin, M. Porkolab, E.S. Marmar, S. J. Wukitch.
   We used a heterodyne electron cyclotron (ECE) system to make observations of both density and temperature fluctuations during discharges with peaked density profiles in the Alcator C-Mod tokamak. ECE systems typically measure electron temperature only; this ECE system was also able to detect density fluctuations in certain cases due to refractive effects. The peaked density profiles were generated by different methods: off-axis ion cyclotron resonance (ICRF) heating, lithium pellet injection and gas puffing. The peaked density profiles generated by off-axis ICRF formed after creation of an enhanced-DAlpha¡ (EDA) H-mode. The EDA H-mode has an edge transport barrier which co-existed with the core peaked density profiles. The low particle confinement of the EDA H-mode is attributed to a quasi-coherent (QC) mode producing increased impurity transport in the edge pedestal region. Similarities between the QC mode and the observed coherent density and temperature fluctuations in the plasma interior are discussed. In peaked density profiles generated by pellet injection, broadband density fluctuations were observed. Implications of these core and edge fluctuations for understanding transport in peaked profiles and the EDA H-mode are discussed.