Theory Weekly Highlights for January 2010

January 29, 2010

A new eigenvalue solver for GYRO, based on finding roots of the plasma dielelctric function, has been developed. The advantage of this approach over the distribution-function-based eigenvalue solvers that currently exist in GYRO and GENE is the significantly smaller matrix size. The matrix size for the eigenvalue problem for a standard test case is reduced from 10240 by 10240 to only 24 by 24. This new solver has proven extremely useful for the study of high-beta plasmas like NSTX, which exhibit an eigenvalue spectrum with many closely spaced roots that are at best problematic to compute with the initial-value approach.

January 22, 2010

Dr. Vincent Chan was awarded the 2009 China International Science and Technology Cooperation Award on January 11, 2010 in a ceremony attended by top government officials. This prestigious award is given annually to people designated as having contributed to China's science and technology development by the Chinese Ministry of Science and Technology. Dr. Chan was honored among the seven 2009 recipients for his contributions to the promotion of US-PRC fusion collaboration leading to rapid progress of nuclear fusion research in China. The awards were conferred at a ceremony held for China's annual national science and technology awards in the Great Hall of the People in Beijing.

January 15, 2010

A new collision model has been implemented in the TGLF model and verified against GYRO simulations. TGLF with the new collision model yields better agreement with GYRO for a database of 64 nonlinear simulations that included Miller geometry and collisions. The average RMS errors in [χi, χe] are significantly reduced to [0.10, 0.13] using the new TGLF-APS09 collision model from [0.24, 0.27] using the original TGLF-APS07 collision model. Recent work has focused on validating the TGLF - APS09 model against DIII-D and JET hybrid and H-mode discharges. Analysis of the results for 34 DIII-D and JET hybrids shows that the predicted temperature profiles agree with the experimental data as well as for a database of 62 DIII-D and JET conventional sawtoothing H-mode discharges. For the DIII-D hybrids, the predicted ion energy transport tends to be close to neoclassical levels while the electron energy transport tends to be dominated by short wavelength TEM/ETG modes.

January 08, 2010

A new predictive model, EPED1.5, has been developed to provide predictions of the pedestal height and width that are completely first principles in the sense that no parameters are fit to observation. Predicting the pressure at the top of the edge barrier (or “pedestal height”) is critical to predicting and optimizing overall confinement and fusion performance of existing and future tokamaks. The new model, building upon previous work on the successful EPED1 model, combines constraints from non-local peeling-ballooning mode onset and local kinetic ballooning mode (KBM) onset to yield a fully predictive model for both the pedestal height and width based on the intersection of the two constraints. In EPED1.5 both the peeling-ballooning and KBM constraints are calculated directly via stability calculations on model equilibria. EPED1.5 has been tested against an initial set of observations on 7 DIII-D and 7 JET discharges. The new model is found to accurately predict the observed pedestal height, with a ratio of predicted to observed pedestal height of 0.97±0.19. This level of agreement is highly encouraging, and further model testing and development is ongoing.

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