In magnetically confined fusion plasmas like tokamaks, transport of heat and particles is dominated by turbulence. Turbulent transport models can be validated using experimental data, using a rigorous methodology and direct comparisons with turbulence measurements. While the transport models capture details of the turbulence very well, and can be used to predict steady-state temperature profiles for ITER and SPARC and other future tokamaks, there remain several outstanding questions. A long-standing enigma in plasma transport consists of the observation that controlled edge cooling of fusion plasmas triggers core electron temperature increases on time scales faster than an energy confinement time, which has long been interpreted as strong evidence of nonlocal transport. A novel integrated modeling tool, that we call PRIMA, leverages the new trapped gyro-landau fluid transport (TGLF) model that includes multi-scale physics. This modeling tool has been used to interpret data from C-Mod and develop predictions for new experiments at DIII-D. The interpretive analysis at C-Mod shows that the steady-state profiles, the cold-pulse rise time, and the disappearance at higher density measured in these experiments are well matched by the new TGLF model. This provides new evidence that the existence of nonlocal transport phenomena is not necessary for explaining cold-pulse experiments in tokamak plasmas. Predictive analysis was used to design a new experiment to leverage the new Laser Blow-Off (LBO) system at DIII-D, to test whether or not cold pulse inversion will occur on DIII-D, and if it does occur, to test whether the model can accurately predict the plasma conditions where it occurs. Detailed interpretive and predictive analysis from the C-Mod and DIII-D tokamaks will be presented, to make the case that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-pulse experiments in tokamak plasmas. This work has helped improve confidence in predictive capabilities for ITER, SPARC and other future tokamak experiments.
Anne White / MIT
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