Edge momentum transport by neutrals
Conference contribution, 2016
Due to their high cross-field mobility, neutrals can contribute to momentum transport even
at the low relative densities found inside the separatrix and they can generate intrinsic
rotation. We use a charge-exchange dominated solution to the neutral kinetic equation,
coupled to neoclassical ions, to evaluate the momentum transport due to neutrals. Numer-
ical solutions to the drift-kinetic equation allow us to model the intermediate collisionality
typical of the tokamak edge. In the edge there are several processes likely to contribute to
momentum transport in addition to neutrals. Therefore, we present here an interpretative
framework that can evaluate the momentum transport through neutrals based on radial
plasma profiles. We demonstrate its application with representative artificial profiles and
an analytical equilibrium, with parameters typical of L-mode in a medium-sized tokamak.
The magnitudes of the torques we find here due to neutrals are 0.5–5 N·m, motivating the
application of our framework to experimental data, where it will allow us to evaluate the
importance of the momentum flux due to neutrals compared to other transport mechanisms.