Download or read book The Quasi-coherent Signature of Enhanced D Alpha H-mode in Alcator C-Mod written by Joseph Allan Snipes and published by . This book was released on 2001 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: The steady-state H-mode regime found at moderate to high density in Alcator C-Mod, known as Enhanced D alpha H-mode (EDA), appears to be maintained by a continuous quasi-coherent (QC) mode in the edge steep gradient region. Large amplitude density and magnetic fluctuations with typical frequencies of %7E100 kHz are driven by the QC mode. These fluctuations are measured in the steep edge gradient region by inserting a fast scanning probe containing two poloidally separated Langmuir probes and a poloidal field pick-up coil. As the probe approaches the plasma edge, clear magnetic fluctuations were measured within %7E 2 cm of the last closed flux surface (LCFS). The mode amplitude falls off rapidly with distance from the plasma center with an exponential decay length of kr approximately equal to 1.5 cm-1, measured 10 cm above the outboard midplane. The root-mean-square amplitude of the poloidal field fluctuation extrapolated to the LCFS was approximately 5 G. The density fluctuations, on the other hand, were visible on the Langmuir probe only when it was within a few mm of the LCFS. The potential and density fluctuations were sufficiently in phase to enhance particle transport at the QC mode frequency. These results show that the quasi-coherent signature of the EDA H-mode is an electromagnetic mode that appears to be responsible for the enhanced particle transport in the plasma edge.