Validation of a Comprehensive First-Principles-Based Framework for Predicting the Performance of Future Stellarators*

Turbulence remains a significant obstacle for stellarator confinement. Using the most powerful supercomputers, it is now feasible to analyze turbulence across the plasma volume with gyrokinetic codes. Before using such codes, validation studies are necessary to ensure accuracy relative to experimental results.

In this talk, we showcase the results of the successful comprehensive validation of the GENE(-3D)-KNOSOS-Tango framework for predicting the steady-state plasma profiles in a stellarator. This extensive validation study is a first-of-a-kind for stellarators. This framework couples the gyrokinetic turbulence codes GENE and GENE-3D, the neoclassical transport code KNOSOS, and the transport code Tango in a multiple-timescale simulation loop.

We selected four OP1.2b W7-X scenarios with different turbulence characteristics. We perform ion-scale kinetic-electron and electron-scale adiabatic-ion simulations to evolve the density and temperature profiles. The simulated profiles agree very well with experimental data while turbulence properties, such as density fluctuations and heat diffusivities, mirror the observed trends. Key effects are also touched upon, such as electron-scale turbulence and the neoclassical radial electric field shear.

The validation of the GENE(-3D)-KNOSOS-Tango framework enables us to make credible predictions of physical phenomena in stellarators and reactor performance. This is of utmost importance today, when fusion start-ups worldwide are using simulation codes to design power-generating machines for the near future.