Good agreement was found between the dependence of the observed pedestal height on pedestal width and other control parameters such as plasma shape and density, in discharges from the DIII-D pedestal database, with the predicted trends of the stability boundaries calculated with ELITE for a series of model equilibria. This agreement suggests that the DIII-D pedestal is limited by peeling-ballooning stability. It also shows that the model equilibria are sufficiently accurate that this technique can be used to estimate trends in pedestal height as a function of pedestal width and control parameters in both present and future experiments.
Vincent Chan, Ron Waltz, Jon Kinsey, Philip Snyder, Lang Lao, Ming Chu, and Rip Perkins represented our group at the IAEA meeting in Lyon, France. Snyder gave an oral presentation on “ELMs and Constraints on the H-Mode Pedestal: A Model Based on Peeling-Ballooning Modes”. Waltz, Kinsey, Lao, Chu, and Perkins had poster presentations describing the GYRO gyrokinetic turbulence simulations, GLF23 simulations for ITER, FIRE, and IGNITOR, our ITER modeling work, resistive wall and feedback modeling, and Current Hole theory. Snyder and Lao also attended the ITPA pedestal meeting in Garching, Germany and highlighted our edge modeling work.
The ECCD module developed by Y.R. Lin Liu has been implemented in the TORAY-GA ray tracing code. The previous version of TORAY-GA, used R. Cohen's original implementation of the ECCD model and the user needed to manually replace this by the Lin Liu ECCD module in order to use it. In principle, the Lin Liu model is both simpler and superior to the original Cohen model, though in practice, the differences are typically of the order of 10%. The user can now choose either model for the ECCD calculations in the input file “toray.in”, with the new Lin Liu model as the default if none is specified. The new model also has the capability to include collisionality corrections. These are still to be implemented but in the meantime, the new version of TORAY is expected to be released publicly soon.
The US Fusion Grid is now being used to perform scientific data analysis at DIII-D. Developed under the auspices of the National Fusion Collaboratory Project , the Fusion Grid presently consists of MDSplus and SQL data servers at C-Mod and DIII-D, and the TRANSP code located on a linux cluster at PPPL. This computational grid is now being used by scientists at DIII-D for the TRANSP analysis that is being presented at the IAEA and APS/DPP meetings. To tie into the Fusion Grid, new tools were created at DIII-D to allow for preparation of TRANSP input data as well as invoking the TRANSP computation. The advantages to this mode of operation are a greatly improved data analysis throughput rate combined with instant access to the latest version of TRANSP.
A theoretical framework is being developed to solve the coupled, steady-state heat diffusion and Grad - Shafranov equilibrium equations simultaneously, in order to find self-consistent pressure and safety factor profiles for what may be considered as an ultimate vision of a steady-state tokamak reactor. In this framework, the plasma current arises almost entirely from the pressure gradient via the bootstrap mechanism, and the pressure gradient, in turn, is determined by heat conduction with a thermal diffusivity that depends on the poloidal field associated with the plasma current. Under circumstances where the confinement improves with increasing negative shear, a solvability condition for the self-consistent profiles can arise. This may call into question the feasibility of such a fully steady state, tokamak fusion reactor.
These highlights are reports of research work in progress and are accordingly subject to change or modification