The effects of magnetic error fields due to toroidal asymmetry in the external shaping coils were evaluated using a perturbation approach. In this approximation, the plasma is assumed to remain nearly axisymmetric, with the 3-D effects assumed to arise entirely from the external asymmetric coils. The magnetic topology is then computed using a Green's function method, based on reference axisymmetric experimental DIII-D equilibria from EFIT. The results show that a 1 to 2 cm radial shift in the outer upper shaping coils can lead to the formation of a stochastic magnetic field region at the edge with an observable distortion of the plasma shape. These results suggest that the toroidal asymmetry of the external shaping coils may play a role in the differences between the plasma separatrix location reconstructed from EFIT using magnetic and MSE data and that inferred from Thomson edge Te measurements in upper single-null and double-null H-mode discharges.
A DOE review of the GA theory grant was held on July 19-20. Steve Eckstrand from DOE and four panel members from other institutions heard overviews of the theory program on MHD, confinement and transport, and heating and fueling. They also heard topical presentations on edge stability, transport modeling and innovative confinement concepts. Discussions were held on the synergism of the theory program with the DIII-D experiment, and how theory resources are managed.
A Data Analysis Monitoring system (“DAM”) has been developed to monitor between-shot physics analysis for DIII-D. This new system allows for rapid detection of discrepancies in diagnostic measurements or the results from physics analysis codes. This enables problems to be detected and possibly fixed between shots as opposed to after the experimental run has concluded, thus increasing the efficiency of experimental time. An example of a consistency check is comparing the stored energy from integrating the measured kinetic profiles to that calculated from magnetic measurements by EFIT. The system is based on a Java servlet using CLIPS expert system logic and HTML to display the status to experiment operators and Data Analysis Group personnel.
These highlights are reports of research work in progress and are accordingly subject to change or modification