### Theory Weekly Highlights for October 2010

##### October 29, 2010

The solution of the Grad-Shafranov equation for avalanche-generated plateau-phase runaway electron (RE) currents generated by disruptions was extended to calculate the inductive electric field profile in the plasma associated with the dissipation of the current, assuming two decay scenarios. For “passive” decays the Ohmic coils are idle, and mixed boundary conditions are used for both the accumulated flux change and E-field. Active decay whereby the inverted Ohmic coil current is programmed to force the surface electric field to zero during the plateau the boundary condition is trickier. In the “ultimate” active case where E = 0 at the surface throughout the entire disruption, corresponding to an ideal wall or infinite wall time, there is slightly more rapid RE current dissipation because the electric field in the plasma is lower (E – E_{crit} is more negative), but E is not zero, as was cautiously assumed in the DIII-D experimental interpretations reported at IAEA. In ITER, the RE current conversion fraction is 63% for passive decay but is substantially lower at 24% for extreme active decay (ideal wall case). With no extra particle injection, the numbers do not change significantly at 100 ms into the plateau phase.

##### October 22, 2010

Ming Chu and Lang Lao attended the Second Seminar Meeting for the Scientific Advisory Committees for the Center for Magnetic Fusion Theory (CMFT), of the Chinese Academy of Science in Hefei, China on October 18-19, 2010. CMFT is a research unit set up to support theory and modeling for the EAST superconducting tokamak. Ron Waltz and Alan Turnbull attended the Fourth International Workshop on Fusion Theory and Simulation at Peking University in Beijing, China and the opening of the new Fusion Simulation Center at Peking University on October 22.

##### October 15, 2010

The GA Theory group was well represented at the 23rd IAEA Fusion Energy Conference in Daejon, Korea October 11–16, 2010 with three oral talks by V.A. Izzo, J.E. Kinsey, and P.B. Snyder on “Runaway Electron Confinement Modeling for DIII D, Alcator C-Mod, and ITER,” “ITER Predictions Using the GYRO Verified and Experimentally Validated TGLF Transport Model,” and “A First Principles Predictive Model of the Pedestal Height and Width: Development, Testing, and ITER Optimization with the EPED Model,” respectively. In addition, three poster presentations by E.M. Bass, M. Choi, and M.S. Chu were presented. These were respectively on “Gyro-kinetic Simulations of Energetic Particle Driven TAE/EPM Transport Embedded in ITG/TEM Microturbulence,” “Finite Orbit Monte-Carlo Simulation of ICRF Heating Scenarios in DIII-D, NSTX, KSTAR, and ITER,” and “Response of a Resistive and Rotating Tokamak to External Magnetic Perturbations below the Alfven Frequency.” V.S. Chan also had a rappateured talk “A Fusion Developpment Facility on the Critical Path to Fusion Energy” presented by M. Peng of ORNL.

##### October 08, 2010

The new version of Web Portal for the SWIM (Simulation of Wave Interactions with Magnetohydrodynamics) Project- http://swim.gat.com:8080 has been developed and deployed by the Data Analysis and Applications Group. This web portal provides real-time status of SWIM physics simulations running on multiple super computers, such as Jaguar of ORNL and Franklin of NERSC. Its interactive interface allows users to interactively search, sort, rate, comment and purge the archived simulations. This new version of the Web Portal has been deployed in the early 2010 and continuously improved. A mobile/Smart phone friendly version has also been released.

##### October 01, 2010

Iterative simulations of the 5-D finite-orbit Monte-Carlo ORBIT-RF code coupled with the 2-D full-wave AORSA code reproduce experimentally observed outward spatial shifts of FIDA signals in DIII-D and NSTX moderate to high harmonic ICRF heating experiments. The simulations (see highlight from July 16 2010 at Theory Weekly Highlights for July 2010) include quasi-linear and collisional orbit diffusion and finite drift orbit effects. The outward radial shift is due to large orbit drifts of fast ions across the magnetic surfaces, which cannot be reproduced when finite drift orbit effects are ignored. Preliminary simulations for proposed fundamental minority ICRF heating scenarios in ITER and KSTAR suggest that the finite orbit effect may significantly modify the fast ion velocity space distribution in some scenarios. With lower power density case in ITER, the finite orbit effects appear to average out the strong anisotropy to produce a more isotropic distribution. For the higher ICRF power density scenario in KSTAR, the finite orbit effect modifies the symmetrically distorted distribution to produce an asymmetric rabbit ear feature. Further investigation is underway.

**Disclaimer**

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