Theory Weekly Highlights for June 2015

June 26, 2015

A new pilot program called STAR (Simulated Tokamak Advanced Results) was launched at the DIII-D science meeting June 26. The STAR program will engage a team of theoretical modelers to predict the properties of the plasma that are important to the success of an experimental proposal as part of the planning process. These predictions will then be compared to the experimental results and to post-validation of the models. Leaders of approved experiments are invited to submit a proposal to the team of modelers for selection for the STAR treatment. It is expected that this intense planning will result in greater success at achieving the experimental goals.

June 19, 2015

The effect of collisions on linear gyrokinetic drift waves has been studied with the new CGYRO code. CGYRO is a gyrokinetic code that uses the NEO pitch-angle/energy velocity space coordinates with a pseudo-spectral numerical method to optimize the accuracy of the collision dynamics, which are expected to be significant in the tokamak edge. Unlike the GYRO code, which includes only Lorentz pitch angle scattering, CGYRO implements the full, multi-species linearized Fokker-Planck-based model of Sugama, including finite-k⊥ corrections. The code has been successfully benchmarked with GYRO, GS2, and GENE. A study of the effect collision models on linear drift mode stability finds the error in the Lorentz model compared with the full collision model is small (< 5%) for ITG and KBM modes but stronger for TEM modes, where using only the Lorentz model leads to an overestimate of the growth rate by about 10% for moderate collisionality. This is primarily due to the lack of energy diffusion in the pure Lorentz model. Regarding the field particle components, which are often neglected, it was found that momentum conservation has a negligible effect, while energy conservation is essential. Finite k⊥ collisional corrections are generally negligible, but can stabilize weakly growing pure TEM modes at intermediate kθ (kθ ρi ~ 2-3).

June 12, 2015

A new EFIT version “ 06/04/2015” with new magnetic probes and other enhanced features has been released this week on all GA DIII-D Linux stations. All previous inactive magnetic probes in the 67-degree toroidal plane have been replaced with new ones from other toroidal planes. This new version also includes a more comprehensive compensation to external magnetic signals as well as a capability to compute perturbed equilibria based on a reference G EQDSK file by variations of upper and lower elongation and triangularity and displacement of the geometry center. Other enhancements include a capability to output a new set of self-described OMFIT “O” format graphic data files as well individual standard “PL” format EFIT graphic data files. The MPI EFIT version for DIII-D between-shot analysis has also been updated.

June 05, 2015

The resistive-wall model in the M3D-C1 3D MHD code has been verified by comparing the growth rate of a resistive wall mode against an analytic solution. The analytic solution is obtained using a reduced (two-field) model in straight cylindrical geometry with a thin-wall approximation. When M3D-C1 is run using the same model and geometry, excellent agreement is found between the calculated and analytic growth rate in both the resistive and inertial limits of the mode, and in the intermediate regime. Additional tests will be carried out to verify the growth rate for resistive walls of arbitrary thickness, which is a unique capability of M3D-C1 among existing extended-MHD codes.

Jeff Candy, Nate Ferraro, Chris Holland, Orso Meneghini, Phil Snyder, and Alan Turnbull attended the DOE FES/ASCR Planning Workshop on Integrated Simulations for Magnetic Fusion Energy Sciences in Rockville, MD June 2-4. Jeff Candy chaired the Whole Device Modeling Panel and Phil Snyder co-chaired the Plasma Boundary Physics Panel.

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