Advances in plasma-wall boundary conditions for gyrokinetic and fluid simulations

Controlling the energy flux to the wall of tokamaks and stellarators is crucial for magnetic confinement fusion energy. Since the width over which the exhausted power is spread depends on the turbulent cross-field transport, among other physics, there has been an increasing interest in developing fluid, gyro-fluid and gyrokinetic codes that can describe that turbulence. The gyrokinetic and fluid descriptions are not valid in layers of the order of the gyro-radius and of the collisional mean-free-path that form over the wall. These layers provide the boundary conditions for the gyrokinetic and fluid equations. Using the smallness of the angle between the magnetic field and the wall, we have developed simplified models for these layers [2-4]. With these models, we will show how these layers depend on parameters such as the electron-ion temperature ratio [5] and the angle between the magnetic field lines and the wall [6], and we will discuss what these layers imply for gyrokinetics and fluid models in the plasma edge.



References

[1] R. Chodura, Phys. Fluids 25, 1628 (1982).

[2] A. Geraldini et al, Plasma Phys. Control. Fusion 59, 025015 (2018).

[3] A. Geraldini et al, Plasma Phys. Control. Fusion 60, 125002 (2018).

[4] A. Geraldini, J. Plasma Phys. 85, 905870113 (2021).

[5] A. Geraldini et al, J. Plasma Phys. 85, 795850601 (2019).

[6] R.J. Ewart et al, Plasma Phys. Control. Fusion 64, 015010 (2022).