Tokamak scenario planning and simulation including the plasma startup phase using the MEQ suite of codes with application to TCV, SPARC and ARC

Tokamak equilibrium calculations are fundamental in the preparation of tokamak scenarios, pre-shot verification of their controllability, and post-shot analysis. The open-source MEQ suite of codes supports the full spectrum of equilibrium problems of practical importance for tokamak operations and includes the LIUQE equilibrium reconstruction code, the FBT inverse equilibrium solver, and the FGS/FGE free-boundary forward (evolutive) solvers. In support of full-pulse tokamak scenario optimization, the inverse solver FBT has been upgraded to include a model for the external circuit current evolution as well as the transition between vacuum and plasma equilibrium phases. This enables extending the GSPulse workflow, currently used for SPARC and ARC pulse planning, to include the plasma startup phase. Optimized coil trajectories for the full pulse evolution including startup, ramp-up, flat-top, and ramp-down can hence be generated in just a few seconds allowing integration in tokamak design or higher-level pulse optimization workflows. Following the scenario planning phase, closed-loop evolutive simulations of the scenario can be run with a magnetic controller in the loop, choosing between rigid, linearized, linear-time-varying and fully nonlinear plasma models. Illustrative examples for TCV, SPARC and ARC show the generality and capability of the workflow.