Theory Weekly Highlights for August 2001

August 24, 2001

In collaboration with S. Kruger of SAIC, a new standardized tree structure for storing data from stability code runs with either NIMROD or GATO has been agreed upon and is being implemented in MDSplus. The tree structure contains a code specific branch and a comparison branch. In the latter branch, the equilibrium data, plasma displacements, and perturbed fields are stored in a uniform manner so that comparisons between codes and with experimental data are greatly facilitated. This will also allow a set of general analysis tools to be developed independently of which code produced the data. An infrastructure is being created and tested to read the GATO and NIMROD output and store the data in the MDSplus tree upon the completion of a code run.

August 10, 2001

The continuum gyrokinetic turbulence code GYRO has explored the finite rho-star effects of profile shear stabilization and broken gyroBohm scaling. For ITG adiabatic electron cases, the code with noncylic radial boundary conditions reproduces flux tube cyclic boundary condition results in the absence of profile variation. With profile variation, an adaptive source technique has been successfully used to maintain the equilibrium plasma profiles. The key result is that when profile shear is weak compared to the growth rate, there is little profile shear effect and gyroBohm scaling is found. Near threshold with very peaked density gradient lengths, strong self consistent diamagnetic ExB shear, and very sheared profiles, Bohm scaling or worse can be found. These results will be described in an invited talk at the next APS meeting.

August 03, 2001

The normal mode approach for the feedback stabilization of the resistive wall mode (RWM) has been applied to a model DIII-D plasma equilibrium in the absence of toroidal rotation. In this approach, the magnetic signals from the plasma instability and that from the external feedback coils are decomposed into the normal modes of the open loop feedback problem to investigate their resultant stability in the presence of the feedback circuit. Initial results indicate that the coupling of the present feedback coils and sensor loops to the stable RWM's is too strong, whereas their coupling to the unstable RWM is not strong enough. The strong coupling to the stable RWM's hinders the feedback action on the unstable RWM of the present coil arrangement. Substantial filtering of the sensor signals from the stable RWM's is needed to restore the stabilization action on the unstable RWM.

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