Theory Weekly Highlights for November 2010

November 24, 2010

As discussed in the July 9 highlight Theory Weekly Highlights for July 2010), residual stress refers to the remaining toroidal angular momentum (TAM) flux when the fluid toroidal (or parallel) velocity and its shear are made to vanish by balancing any intrinsic (spontaneous) toroidal rotation with a known neutral beam injection TAM source. The small diamagnetic velocity shear remaining when the plasma is at rest contributes to this residual stress. Recent GYRO simulations found the contributions to both the residual stress and stabilization of turbulence from the ExB velocity shear, γE, and the velocity shear components γn and γT, to the diamagnetic flows, while small, are comparable and additive. γn and γT are associated with “profile shear” in the ion and electron density and temperature gradients, and are possibly important in the steep gradient edge. Fixed profile global core GYRO simulations of a balanced injection DIII-D discharge (125229.3500) matched the core residual stress within the measurement uncertainty on γn and γT. Energy and plasma transport flow balance from global GYRO simulations of the core of a well studied high rotation DIII-D L-mode (1010391.2790) was able to isolate and quantify the ExB shear pinch and Coriolis force pinch components of the TAM transport from the larger diffusive parallel velocity shear driven component and the much smaller residual stress.

November 19, 2010

Phil Snyder was elected a Fellow of the American Physical Society at the recent 52nd American Physical Society Meeting in Chicago for his “pioneering contributions to the understanding of the H-mode pedestal and edge localized modes in tokamaks, and for theoretical and computational advances in electromagnetic plasma turbulence research.”

Drs. Qilong Ren completed a three month visit and Aiping Sun completed a six month visit to GA to collaborate on the development of the IMFIT integrated modeling project and its applications for analysis and comparison of DIII-D, EAST, and HL-2A experiments. Dr. Ren returned to ASIPP and Dr. Sun returned to SWIP.

Valerie Izzo and Alan Turnbull attended the Fifteenth MHD Control Workshop in Madison Wi from November 15 through 17, presenting talks on “Theory and Modeling of Disruptions” and “On the relation between 3-D equilibrium and stability,” respectively.

November 12, 2010

A new interpretation of energetic particle (EP) transport is emerging from consideration of recent nonlinear, multiscale simulations in GYRO. In a newly revealed “soft onset” EP transport regime, microturbulent interactions cause Alfven eigenmodes to saturate at much lower intensity than predicted by Alfven mode self-interaction models. Strong EP transport, manifesting as runaway GYRO simulations, appears only at a critical EP gradient well above the Alfven linear threshold. We now understand that this critical gradient depends on the thermal-species profiles through ITG/TEM drive. At fixed EP drive, weak EP transport results when sufficiently strong ITG/TEM fluctuations are present. Strong transport does not necessarily appear at the point of Alfven linear instability as previously expected. The true location of the strong transport EP critical gradient (as a function of thermal-species gradients) gives an approximate upper limit on the EP pressure gradient and suggests a simple model to predict the Alfven transport-limited EP pressure profile.

November 05, 2010

At the recent Second Seminar Meeting for the Scientific Advisory Committees for the Center for Magnetic Fusion Theory of the Chinese Academy of Science in Hefei, China (see highlight for October 22 at Theory Weekly Highlights for October 2010), Lang Lao discussed the topic of experimental integrated modeling using the IMFIT Integrated modeling project and the ITER Integrated Modeling Program as working examples. He also summarized the recent progress in the IMFIT project. The first version of IMFIT has been released which includes magnetic and kinetic EFIT reconstruction, transport and stability analysis for DIII-D. This version will be available also for EAST shortly. Efforts are ongoing to add TGLF, NTV momentum transport, pedestal physics, energetic particle physics, and 3D equilibrium and reconstruction capabilities.

Gary Staebler will present his invited talk “Discoveries From the Exploration of Gyrokinetic Momentum Transport” at the upcoming 52nd APS Meeting in Chicago in session PI2 Wednesday Nov. 10, 2PM-5 PM.

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