  Plasma edge simulation with the SOLPS-ITER code are performed to study the
influence of divertor baffles on nitrogen-seeded detachment in L-mode TCV
discharges. Simulations of nitrogen seeding with baffles is found to yield
lower target temperatures and heat fluxes than in baffle-only and seeding-only
simulations. The neutral compression increases with both baffles and seeding,
but due to different mechanism according to the proposed neutral transport
model. The nitrogen retention, defined as the divertor-to-main chamber nitrogen
density ratio, increases with the seeding rate if baffled. Baffled nitrogen
retentions are lower than the unbaffled retentions at low seeding levels and
are higher at high seeding levels. The baffled carbon retentions are always
above the unbaffled retentions due to increased target particle flux and
sputtering by baffling. Baffles also relocate more impurity radiations from the
main chamber region into the divertor. The predicted trends of target
parameters, radiation and neutral distributions are well supported by TCV
experiments, though discrepancies in absolute values remain. The simulations
generally yield a colder and denser divertor, consistent with previous
SOLPS-ITER simulations of Ohmically heated L-modes in TCV. The comparison of
simulation and experiment, together with the proposed neutral transport model,
suggest the necessity of sufficient baffling in future TCV divertor upgrade,
and a combination of baffling and seeding to facilitate the access to
detachment.
