Theory Weekly Highlights for August 2003

August 29 2003

The new MDSplus server Atlas has been installed. It is currently serving MDSplus data, and will be integrated into the MDSplus between-shot loading system in time for the upcoming operations period. This Quad Xeon Linux server can handle much greater loads than the old Alpha 800 5/500 Tru64 server. For the time being, old MDSplus data will remain on the old server and served transparently through the new server; new MDSplus data will go onto the new server. The long-term plan is to migrate all data onto a direct-attached mass storage system when funds are available. At that point all data will be served through the new MDSplus server.

August 22 2003

In collaboration with Dr. S.C. Guo from Consorzio RFX, the theory for the dynamic development of the electromagnetic torque acting on an RFP plasma by a resistive wall was extended to self-consistently include plasma angular momentum transport as well as the effect of the mutual coupling of multiple dynamo (tearing) modes. The equations provide an understanding of the relative importance of angular momentum transport due to mode coupling versus the resistive wall torque in the wall locking and slinky formation processes. Also, the presence of multiple modes was found to greatly reduce the mode-locking threshold. The previously employed steady state theory for the determination of the resistive wall torque is shown to produce valid results when the time scale involved is much longer than the response time of the resistive wall. When the time scale is shorter than the resistive wall time, the development of the torque depends on the details of the time history of the tearing instability. The theory can also be extended to the study of stabilization by a resistive wall in tokamak plasmas.

August 15 2003

The fluctuation terms describing the effect of turbulence in the averaged drift kinetic equation, including the turbulence-driven current and its modification by electron trapping, have been incorporated into the standard banana regime neoclassical transport calculation. In the resulting neoclassical Ohm's law, an EMF due to turbulence is added to the inductive electric field; the usual neoclassical resistivity multiplies the difference between the parallel current and the bootstrap current, as usual. The turbulence modifications to Ohm's law, assuming massless electrons can be identified with the MHD alpha dynamo effect. This dynamo EMF could be significant in reactor-scale machines because of their small inductive EMFs, and could help or hinder maintaining the current, depending on its sign. A more general expression for the dynamo EMF, including electron inertia, was also derived, which has the form of the divergence of a flux and depends on statistical correlations between moments of the fluctuating distribution function and the electric and magnetic field fluctuations. We are currently attempting to evaluate this expression using the GYRO code.

August 01 2003

As part of the Big Splash project, which is a large computer time award given annually by NERSC, for state-of-the-art, computationally demanding numerical simulations, the NIMROD code is being used to model NTM onset and evolution in a sawtoothing ITER simulation with a variety of realistic physics models. Several ITER equilibria based on DIII-D discharge 86144 were generated and run nonlinearly, and reproduced the sawtooth seeding of a 3/2 NTM. The Poincare surface of section for a sawtooth crash simulation in ITER geometry and the contours of the electron temperature at that time are topologically congruent at realistic values of anisotropy in the heat conduction, and show pressure flattening within the islands. The simulations for this ITER case are based on previous work on sawtooth seeded NTM simulations in DIII-D and the ITER results will be compared to the earlier DIII-D simulations. Neoclassical bootstrap drive effects are being included next. These calculations are challenging, but promising.

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