Arc stabilization is reached by a gas  vortex ring in the annular chamber surrounding the anodic  nozzle and the tungsten electrode; the mass of whirling  plasma gas tends to align the pilot arc according to the  torch axis and therefore helps in addressing the arc  inside the nozzle (plenum chamber).

Pinch effect  is the result of the magnetic field force pushing pilot  arc into the nozzle bore towards the external side and  then returning back to the anodic spot region, with an  airpin path between anode and cathode.

Fig. 1 -  Anodic Nozzle - Pinch effect