Parallel Flow in the JET Scrape-Off Layer

Parallel plasma flows with Mach number M ≈ 0.5 have been measured in the JET SOL. These flows show a maximum some 10–20 mid-plane mm outside the separatrix, and decrease towards the separatrix. The flow reverses when BT and IP are reversed, but is asymmetric about zero. Modelling suggests that a contributor to the observed flow is the co-current toroidal momentum generated in the SOL by ion ∇B and classical (diamagnetic) drifts, together with ion Pfirsh-Schlüter flow.