Assessment of thermo-electric techniques for scrape-off layer current drive in flux-tube geometry

The magnitude of the parallel current that can be driven by asymmetries between divertor target plates is calculated in magnetic flux-tube geometry. Current can be driven between ends of the flux-tube by passive techniques that generate a thermo-electric potential by heating or cooling one side relative to the other through pumping or neutral gas injection. The induced thermo-electric potential depends on the total particle flux pumped relative to the total recycling flux. For the geometry considered, pumping efficiency is higher for pumping by the target plate or from the private flux zone than for pumping from the outer side of the plate. Neutral gas injection is not as effective at generating an asymmetry. An important constraint for these methods may be the additional heat flux delivered to the hotter target, but additional Ohmic heating is much smaller than that generated by electrical biasing.