1. Does quasi-coherent mode limit pedestal pressure gradient?
Rich Groebner1, Jerry Hughes2, Phil Snyder
1General Atomics, San Diego CA, USA
2MIT Plasma Science and Fusion Center, Cambridge, Massachusetts, USA
Presented at the
C-Mod Ideas Forum
April 7, 2009

2. Motivation: Study pedestal limiting phenomena in C-Mod
Studies in C-Mod suggest that there may be a critical pressure gradient in the pedestal
The Quasi-Coherent Mode is a candidate mechanism for limiting the pressure gradient
There is some evidence that this could be happening, but evidence not definitive
Goal of experiment would be to obtain high quality, temporally-resolved pressure profiles to study this idea
Experiment complementary to a study in DIII-D for evidence that kinetic ballooning modes limit the pressure gradient

3. Execution of experiment
Set up discharge which develops a robust, saturated QCM
The QCM should evolve for a few tens of milliseconds prior to saturation
Quantify strength of QCM with fluctuation diagnostics
Obtain time-resolved measurements of pedestal pressure profile during growth and saturation of QCM
Thomson Scattering will be key
Perform multiple repeat discharges to build up record of temporal evolution of pressure gradient
Look for saturation of gradient when QCM reaches max strength