ComPat framework for multiscale simulations applied to fusion plasmas

Understanding the dependency between plasma turbulence and overall transport is essential in predicting the performance of fusion devices. This dependency is not fully understood because of the highly disparate spatio-temporal scales involved, which prohibits a fully-resolved turbulence simulation at transport scales. The Computer Patterns for High Performance Multiscale Computing (ComPat) project takes the component based approach for multiscale simulations to connect existing single-scale models into a workflow. In this paper, we present the ComPat's approach in building a multiscale fusion application: it brings equilibrium, transport and turbulence models together, where the turbulence is described by a 3D gyrofluid code. Initial results and challenges encountered with such approach are also presented and discussed. One of the challenges is to ensure numerical stability, for which adaptive time step size and the search for quasi-steady state are implemented as possible solutions. Another challenge is to improve the overall performance of multiscale simulation, and that is addressed by increasing the level of parallelism to the workflow. (C) 2019 Elsevier B.V. All rights reserved.