New Fluctuation Phenomena in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>H</mml:mi></mml:math>-Mode Regime of Poloidal-Diverter Tokamak Plasmas

Abstract

A new kind of fluctuation is observed near the edge of plasmas in the PDX tokamak operating in the "$H$-mode" (improved-confinement) regime. These fluctuations are evidenced as vacuum-uv and density-fluctuation bursts at well-defined frequencies ($\frac{\ensuremath{\Delta}\ensuremath{\omega}}{\ensuremath{\omega}}\ensuremath{\lesssim}0.1$) in the range between 50 and 180 kHz. The bursts are correlated, both in space and in time, with changes in the temperature-density product near the plasma edge where large density and temperature gradients develop during the $H$ mode.