A Gyrokinetic moment-based method to model the plasma boundary of fusion devices at arbitrary collisionality

We present a new first-principles model that allows for the proper simulation of the tokamak plasma boundary [1,2]. Developed onto a set of fluid-like equations that retain the gyrokinetic Coulomb collision operator, the gyro-moment (GM) model offers a modeling framework able to describe the fluctuations occurring on a large range of spatial scales present in the plasma boundary where the plasma collisionality can vary by orders of magnitude. The GM model contains the core gyrokinetic model and the fluid and gyrofluid models used for scrape-off layer simulations as particular limits. We illustrate the analytical and numerical capabilities of the GM model. We demonstrate that the GM approach can correctly retrieve the properties of microinstabilities that develop at low plasma collisionality, strongly sensitive to kinetic features, in perfect agreement with the GK continuum GENE code. At the same time, we show that the GM model correctly retrieves the fluid limit at high collisionality by using advanced GK collision operators, such as the GK Coulomb collision operator. Furthermore, we prove that the GM approach is numerically efficient for the simulations in plasma regimes that range from the low-collisionality banana regime in the H-mode pedestal to the high-collisionality regime of the scrape-off layer in L-mode discharges. Our first nonlinear simulations show that, due to deviations in the linear growth rates and zonal flow damping [3,4,5], turbulent transport levels in the boundary can be largely underestimated if commonly used collision operators are used.