Several members of Theory group attended the APS/DPP meeting in Milwaukee, Wisconsin this week. Phil Snyder presented an invited review talk on pedestal physics, Gary Staebler presented an invited talk on core transport, and Brendan Lyons gave an invited talk on predict first simulations.
A neural network nonlinear regression has been developed for fast calculation of the neoclassical bootstrap current for use in edge stability analysis and integrated modeling applications. The network is constructed using the OMFIT integrated modeling framework, which builds the network and compiles databases on which to train it and benchmark its performance. The bootstrap current neural network is trained using a large database of over 57,000 NEO runs. The model assumes a 3 species plasma (electrons, deuterium ions, and carbon impurities). Analytic theory is used to minimize the number of input parameters to 6, describing the geometry (inverse aspect ratio, safety factor, and fraction of trapped particles), collisionality (electron collision rate), and ion-impurity physics (ion-to-electron density and temperature ratios). The NN requires only a few micro-seconds, and performs well for a wide range of DIII-D experimental conditions. It provides an improvement to the Sauter model at high collisionality and for impurity physics. This work will be presented by Arsene Tema Biwole in an oral talk at the upcoming APS meeting in Milwaukee WI.
A new UCSD postdoctoral researcher, Dr. Payam Vaezi, is joining the GA theory group beginning October 16th for a one-year collaboration. Dr. Vaezi's thesis work focused on validation studies of the CSDX experiment at UCSD using the BOUT++ framework, including applications of advanced uncertainty quantification methods. His work with the GA theory group will focus on implementing those methods for use with codes such as TGLF, GYRO, and CGYRO in verification, validation, and integrated modeling studies.
It has been demonstrated (He Sheng et al., Phys. Plasmas 2017) that the gyro-fluid code TGLF can compute energetic particle (EP) instabilities that match gyrokinetic calculations with GYRO. Now, for the first time, it has been found that in DIII-D high poloidal beta discharges, with observable EP modes, that TGLF finds EP modes in the correct location and predicts that they could be having a measurable effect on electron energy transport in DIII-D. This result will be reported in an invited talk by Gary Staebler at the upcoming APS-DPP meeting in Milwaukee.
These highlights are reports of research work in progress and are accordingly subject to change or modification