Parallel SOL flow on TCV

Abstract

Particle flow measurements parallel to the total magnetic field direction have been obtained for the first time in the TCV tokamak scrape-off layer. The plasma shape flexibility of TCV, coupled with carefully matched ohmic diverted discharges in forward and reversed toroidal field at varying plasma density is used to try and separate drift flow components and any field independent contributions in the outboard midplane vicinity. The measurements are generally well described in both direction and magnitude by neoclassical Pfirsch–Schlüter return flows compensating poloidal drifts. There is clear evidence for a small, field independent offset component (∼10–20% of the main flow), whose magnitude would be approximately consistent with a contribution driven by enhanced outboard ballooning particle transport due to interchange motions, but a part of which could also be due to divertor sink action in the rather open TCV divertor configuration.