The influence of atomic collisions on the sheath profile*

Plasma particle and power exhaust to a solid material surface involves

complicated atomic processes including elastic and inelastic

collisions between electrons and neutrals, ions and neutrals, and

neutrals themselves.  These processes set the ionization balance,

radiation loss, and energy and momentum exchange between different species

of plasma and neutrals.  Coupled with particle and energy

recycling at the solid surface, the plasma-material interaction and

atomic processes combine to set the steady-state and transient

particle and power exhaust in a tokamak with diverted plasmas.

The physics over there exhibits strong kinetic nature and thus first principle

PIC simulation is required to deploy the physics. Here

we report the development of an atomic collision package for the

first-principle VPIC kinetic code, and the application of this new

simulation capability to investigate the boundary plasma response to

the particle and energy recycling at the wall.  Of particular interests are

the condition for plasma detachment, and how the atomic processes,

along with particle and energy recycling, impact the plasma sheath

structure.