Fast pedestal, SOL and divertor measurements from DIII-D to validate BOUT++ nonlinear ELM simulations

This paper documents first work toward validation of BOUT++ nonlinear edge localized mode (ELM) simulations in X-point geometry, at experimental pedestal collisionality, against multiple diagnostic measurements of a well-characterized ELM event in DIII-D. The key to the BOUT++ simulations is the use of a hyper-resistivity model that effectively spreads the very thin current sheets that form in low collisionality nonlinear simulations, and allows for ELM driven magnetic reconnection at finite current density. Experimental ELM characterization includes multiple fast line-integrated diagnostic measurements revealing in–out divertor asymmetric response to ELMs, IRTV imaging at the divertor targets, visible emission in the divertor volume to test the extension of BOUT++ to X-point geometry, and forward modeling of new electron cyclotron emission imaging to test predictions of ELM filaments in the edge pedestal. Initial comparisons suggest optimized BOUT boundary conditions and model parameters, and show similarities between initial BOUT++ results and several measurements.