Kinetic Physics in Tokamak Boundary Plasma

Unlike the core plasma, tokamak boundary plasma is in a non-equilibrium or a far-from-equilibrium thermodynamic state. Individual particle orbits can significantly deviate from the usual equilibrium statistical behaviors, transport may not obey Fick’s law, the transport time-scale may not be diffusive, plasma can easily become non-Maxwellian, the conventional fluid closures based on the near-equilibrium thermodynamics –including the well-utilized CGL closure and Braginskii viscosity – may not be valid, and plasma turbulence may not be of usual type seen in the core plasma. A kinetic simulation may be needed for higher fidelity understanding of the boundary physics and for improvement of fluid closures. This talk will introduce the kinetic aspect of the boundary plasma that may not be easily captured by fluid moments equations and that may help improve fluid simulations through collaborative effort. The spatial region of discussion will include the H-mode pedestal, the magnetic separatrix and the X-point, and the scrape-off region that is in contact with the material wall. Neutral particle kinetics will also be discussed. Update on L-H transition dynamics, and SOL and divertor heat-load physics will be discussed as examples.