Theory Weekly Highlights for January 2009

January 30, 2009

The new Web Portal Site ( is being tested for DIII-D operations. The web portal provides current operation information from diverse sources in a unified way with a consistent look and feel. It allows users to personalize the website to fit their individual needs with applications which can be independently customized, enabled/disabled and moved around on the web page with a simple click-and-drag. The portal will be a convenient way for users to access a variety of information from one place.

January 23, 2009

The EPED1 predictive model for the H-mode pedestal (see March 7 2008 highlight at Theory Weekly Highlights for March 2008) has been successfully tested against a large set of pedestal data from the DIII-D, JET and JT-60U tokamaks and shown to accurately predict the observed pedestal height. The pressure at the top of the edge barrier or “pedestal height” is a key parameter for determining global confinement and fusion performance. The EPED1 model combines direct calculations of peeling-ballooning stability, using the ELITE code, with a simple relationship between pedestal width and height, to yield predictions of both pedestal height and width and has been successfully employed to predict pedestal height on DIII-D before a series of dedicated pedestal experiments. The recent extensive test of the model employs pedestal data from the DIII-D (21 cases), JT-60U (16 cases) and JET (4 cases) tokamaks. The model accurately predicted the pedestal height, which varies more than an order of magnitude in the dataset, with a ratio of predicted to observed height of 1.02 ± 0.13.

January 16, 2009

Results from a study of the confinement of fast electrons during a massive gas jet induced disruption confirm experimental observations of a prompt loss of runaway electrons at the time of the thermal quench due to strongly stochastic fields. The study is intended to determine if sufficiently poor confinement precludes the need for collisional runaway electron suppression by exceeding the Rosenbluth density. A post-processing tool was developed to examine fast electron acceleration and confinement using the magnetic and electric fields from NIMROD simulations. In a simulation intended to study the effects of elongation on the resulting MHD spectrum during the disruption, the analysis for a low-elongation equilibrium shows some retention of good flux surfaces in the core immediately after the thermal quench, A detailed runaway electron analysis and comparison with higher elongation simulations remains to be carried out. Near term plans include the incorporation of the runaway electron model to run in real time during the NIMROD simulations, which will improve accuracy by updating the magnetic and electric fields at every time step. An extension of the physics model for the fast electrons to include synchrotron radiation drag and FLR effects is also planned.

January 09, 2009

M3D-C1, a nonlinear two-fluid MHD code being developed by Nathaniel Ferraro at GA in collaboration with S. Jardin and J. Chen at PPPL and X. Luo at RPI, has recently been extended to allow an arbitrarily shaped computational domain. This is a significant improvement that will allow benchmarking with ELITE and NIMROD, and will allow accurate calculations of the linear stability of ELMs with a visco-resistive two-fluid model. Furthermore, this improvement will allow the calculation of the axisymmetric steady-states of this model, which self-consistently includes flows, in DIII-D and ITER geometries and subject to realistic boundary conditions. M3D-C1 is being developed as a general-purpose nonlinear MHD code for the simulation of fusion plasmas on both stability and transport timescales using comprehensive fluid models.

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