Theory Weekly Highlights for March 2021

March 12, 2021

Incorporation of pellet fueling sources into integrated modeling workflows via accurate pellet ablation and deposition is essential for analysis and interpretation of current tokamak pellet experiments and prediction of ITER pellet fueled scenarios. A comprehensive Pellet Ablation Module (PAM) has been developed and implemented as a python module in OMFIT. The module predicts the density source based on an analytical pellet ablation model that includes a deuterium-tritium composite model either in the form of separated deuterium and tritium layers or homogeneous mixtures with arbitrary DT blends. PAM is intended to be executed as either a stand-alone module, or called from other OMFIT integrated modeling workflows. The module is capable of handling general 2D tokamak geometry and can deposit the pellet source onto the transport grid as a point, radial Gaussian, or flux averaged 2-D Gaussian source. Applying PAM to a DIII-D plasma, we find good agreement of pellet deposition to the predecessor model PELLET and reasonable agreement to experiments. The addition of the pellet source from PAM into integrated modeling workflows increases electron and lowers electron temperature with only a small change to the total stored energy, consistent with experimental observations.

March 05, 2021

The presence of static resonant magnetic perturbations (RMPs) can modify both the magnetic field lines and energetic particle (EP) drift orbits, forming magnetic and drift orbit islands, respectively. While the magnetic islands have been studied extensively to interpret thermal confinement changes, EP confinement is determined instead by the drift orbit islands. A comparative study of the drift orbit and magnetic islands was carried out for a 15 MA baseline scenario ITER plasma. The drift orbit island size is comparable to that of the magnetic island and is insensitive to the EP energy. However, passing EPs with outward radial drift form orbit islands that shift inward with respect to the corresponding magnetic islands, and vice versa. Also, it was found that the orbit islands are about three times smaller when including the plasma response, compared to the vacuum field. Trapped EPs do not form drift orbit islands even in the presence of the 3-D fields produced by the 90 kA-t RMP coil current in ITER, implying these are better confined. Nevertheless, deformation of the trapped particle drift orbits in the Poincare plane shows that the canonical toroidal angular momentum for EPs is no longer conserved in the presence of the RMP fields. These results are important for better predicting the confinement of EP particles in ITER.

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