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A set of numerical procedures have been written in IDL
to compute the neutral atomic and molecular hydrogen (or deuterium) distribution
functions in a slab-like spatial geometry with specified plasma profiles.
This paper reports detailed information about the numerical algorithms
and the atomic and molecular physics employed by the code. The top-level
numerical procedure (KN1D) sets up the model geometry, numerical
grid, and boundary conditions and principally calls two sub-programs, one
which handles the spatial evolution of the molecular distribution function
and the resultant velocity space source of atomic hydrogen (Kinetic_H2)
and one which handles the spatial evolution of the atomic distribution
function (Kinetic_H). The model geometry in KN1D consists
(in increasing values of x) of a wall surface, a local limiter shadow
and plasma scrape-off layer (SOL) region, a global SOL region, and a core
plasma. The input parameters are: the 1-D geometric dimensions (limiter,
SOL, and core), plasma profiles (density, ion and electron temperature)
and the molecular neutral pressure at the wall. This geometry simulates
plasma-neutral interaction that might be expected in the main-chamber of
a tokamak with a magnetic divertor or a primary limiter that is remote
from the local limiter. If desired, the sub-program units can be run independently
by appropriately specifying the plasma profiles, numerical grid, boundary
conditions, source profiles, and the other distribution function as input.
The numerical algorithm includes charge exchange collisions, electron-impact
ionization and dissociation, elastic self-collisions (atomic and molecular),
and a variety of elastic cross-collisions (atom-ion, atom-molecule, molecule-ion).
Output parameters include: atomic and molecular distribution functions
and fluid moments, molecular dissociation rate profiles, and molecular
ion density and temperature profiles. A number of numerical consistency
checks are performed in the code involving mesh size limitations and errors
associated with discrete representation of ion and neutral distribution
functions. Optionally, the numerical accuracy is checked by direct substitution
into the Boltzmann equation and reported at each location on the computational
mesh. The source code is entirely written in IDL and is freely available
to the community. |
