Theory Weekly Highlights for February 2007

February 23, 2007

Four members of the DIII-D staff successfully participated remotely in the JET experiment in the UK - “Development of high βN scenarios without ITB” from the GA San Diego site via the remote participation tools of the Advanced Imagery Lab (AIL). Between the February 20 and 21 shifts, 21 JET pulses were run and one of the two top priority goals of the experiment was successfully completed. The experiment was delayed and its pulse schedule was intermittent due to a few hardware problems. This successful participation is a good example of the benefit of remote experimental participation; the ability to rapidly adjust to varying experimental schedules when compared to the fixed schedule of international travel plans.

February 16, 2007

Initial NIMROD simulations with n=1-3 RMP vacuum fields superimposed on the equilbrium as an initial condition show a fast response to the imposed perturbing fields, followed by a subsequent slow growth of kinetic energy predominantly in the n=0 and n=3 components. ExB flows in the form of small convective cells crossing the separatrix appear. As this convection pushes density into the vacuum region, a falling pedestal density is observed. This result provides a mechanism for the enhanced particle transport observed in RMP ELM control experiments. Experimentally, the resulting decrease in the pedestal pressure gradient leads to ELM stabilization. The cause of the localized electrostatic potential variations responsible for the ExB flows is being investigated.

February 09, 2007

Detailed equilibrium reconstructions of a DIII-D fast-wave (FW) discharge with MSE and kinetic data using EFIT show that axial q0 variations are much larger during the giant sawtooth phase than during the regular phase. q0 varies between 0.96 and 1.01 during the regular phase with neutral-beam heating only, but between 0.88 and1.01 during the giant sawtooth phase with NBI plus FW. The axial q0 variations correlate well with the application and change of FW power and central electron temperature from ECE. Transport and stability simulations using ONETWO, ORBIT-RF, GATO, and the Porcelli sawtooth model are underway.

The Mini-Proposal Site for 2007 has been set up. Following the previous year’s structure, the site allows mini-proposal submission, review and approval. A new web-based GUI was created to provide a simpler solution for content management for the final approver.

February 02, 2007

A recently modified version of the 5D δf Eulerian gyrokinetic code EGK (see September 1 2006 highlight at Theory Weekly Highlights for September 2006) that solves the Poisson equation in vorticity form, has been used to successfully simulate neoclassical ion transport, including the self-consistent radial electric field, neglecting the poloidal variation of the electrostatic potential Φ. Using pitch angle scattering collisions and assuming the flux tube limit, this simplified code has reproduced the previously published results showing saturation of the radial electric field (Er), obtained from a radially global simulation. Development of a unified, global EGK code which solves drift wave physics and neoclassical physics using the same algorithms is in progress. This code will extend studies of neoclassical transport to include the effects of the poloidal variation of Er and kinetic electron dynamics.

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