Theory Weekly Highlights for June 1999

June 18, 1999

The nonlinear interaction of drift wave turbulence with sheared ExB or “zonal” flows is being investigated. Equations for the drift wave and zonal flow potentials were derived. In addition to the usual polarization drift nonlinearity, an electron nonlinearity was found, which was found to be essential for energy conservation in the coupled equations for the potentials. This may lead eventually to an understanding of how turbulence in tokamaks is regulated by sheared ExB flows, and a prediction of transport rates.

The general purpose data access routine GADAT was integrated with the Data Analysis Group's IDL code management system. The routine is now documented and automatically available to users through the standardized login scheme. This integration makes it simpler for users to access DIII-D data from within their own IDL codes.

June 11, 1999

A new theoretical model has been developed which explains the observation that inside launched pellets in DIII-D deposit fuel closer to the interior of the plasma than normal outside launched pellets despite the lower pellet speed. The model derives the cross-field movement of the pellet cloud from the vertical grad-B and curvature drifts induced by the 1/R variation in the toroidal field strength and includes the effects of inductive parallel currents and the associated polarization drifts and the finite pellet beta. The vertical drift current leads to a charge-induced electric field build up inside the cloud and the resulting ExB drift velocity is faster than typical pellet velocity. The model predicts that the large-R shift in the fuel penetration is ~ 17 cm, which is consistent with the fuel deposition profile measured within 1 ms after pellet injection.

The transition to Unix MDSplus was completed and DIII-D data is now being served from a Digital Unix Workstation with 100 GB of RAID disk space. Data retrieval performance is at least two times faster than from the old VMS server. Also, the transition opens up 57 GB of space for storing additional analyzed datasets and provides an upgradable path for future expansion in both CPU and magnetic storage.

These highlights are reports of research work in progress and are accordingly subject to change or modification