Kinetic effects in tokamak edge plasmas - nonlocal parallel transport and plasma-atomic reactions

In tokamak edge plasmas, accurate modelling of transport towards plasma-facing components is critical to the successful operation of future devices. These plasmas are often assumed to be collisional, but there are two important (and related) areas in which this assumption may be violated. First, steep temperature gradients parallel to the magnetic field means electron heat transport may be dominated by fast, low-collisionality particles and so becomes ‘non-local’. Second, enhanced high-energy tails of electron velocity distributions close to the walls, where most plasma-atomic interactions take place, may modify reaction rates and therefore affect the particle, momentum and power balance.

For these reasons, tokamak edge plasmas have been investigated using the 1D kinetic electron code SOL-KiT [1] across a wide range of collisionalities. We see increasing kinetic effects, in particular modifications to the heat flux and boundary behaviour, in reactor-relevant regimes. There are also large differences observed (up to 50% suppression) in the predicted radiative losses from non-hydrogenic impurity species, due to kinetic modifications of plasma-impurity reaction rates.

[1] S. Mijin, A. Antony, F. Militello, R.J. Kingham, Computer Physics Communications (2021), 258, 107600.