SOPHIA: A tokamak simulator

SOPHIA is a tokamak simulator developed at Tokamak Energy Ltd. SOPHIA combines a transport code ASTRA coupled with an equilibrium solver SPIDER, a plasma control system and models of the actuators and synthetic diagnostics. The main goal of SOPHIA is to help session leaders and physicists in charge prepare for the experiment by predicting experimental outcome in a simulation given their experiment-defining reference waveforms and settings for the tokamak systems as well as the plasma control system. SOPHIA reads these waveforms and settings directly from the application used by session leaders to prepare real experiments, the Pulse Schedule Editor (PSE). Complimentary to its experimental input interface, SOPHIA simulation outcome is stored using a format and MDSplus data structure identical to that of real experimental results, enabling the use of the same TE applications as for real experimental data analysis – MDSplus Shot Viewer and ST40 Physics Viewer. Thus, SOPHIA is fully integrated with the ST40 experiment and SOPHIA simulation can simply be triggered with a click of a button, and in fact should generally be run prior to every discharge. Currently, SOPHIA can be used in several modes. On the plasma simulation side, one can use the predictive transport calculations in ASTRA code or else fix the pressure profile based on experimental data from a selected discharge, measured by Thomson scattering system. On the plasma control system (PCS) side, there is an option to use PCS internal plasma position estimator module, PFIT, just as in real experiments, and generate its magnetic sensor input from synthetic diagnostics inside SPIDER such as Rogowski coil currents, loop voltages or local magnetic sensors. Alternatively, one can pass on to the controllers the exact plasma parameters that SPIDER computes directly, such as plasma radial and vertical position, X-point locations, gaps to last closed flux surface and plasma current, bypassing the PCS internal PFIT code. SOPHIA’s simulator framework is developed in Simulink and MATLAB environment with effective memory coupling with C and Fortran codes: it can be run directly in MATLAB or as an executable compiled from C. Plasma control system, which includes controllers, supervision and actuator models (actuator models are part of SOPHIA, not part of PCS) is exactly the same as used in the experiments. This extends SOPHIA application to tackle complex control problems where the multi-physics and multiple input/output nature of the system is inherent to the plasma dynamics. Even more, SOPHIA’s integration with PSE manager and other applications used in operations, makes SOPHIA particularly well suited for training new session leaders and the ST40 operators. It speeds up learning curve and increases confidence in preparation for new experiments.