Generates ghost cells for a particular entity so that an updater requiring ghost cells can be used on a subset of the full domain.
onEntity
(string)boundaryName
(string)layers
(integer)<Updater generateVacuumBoundary>
kind = boundaryEntityGenerator2d
onGrid = domain
layers = 2
boundaryName = vacuumBoundary
onEntity = vacuum
</Updater>