Currents in Intersected Tokamak Flux Tubes

In an elementary way the toroidal electric current in tokamaks is considered if the flux tube is intersected by limiters within the Scrape Off Layer (SOL). Simple sheath conditions are applied. The limiter space charge sheaths act as additional resistances, consuming partly the available voltage and diminishing the current density which is limited both by the plasma conductivity and by the ion saturation current of the sheaths. The difference between both potential drops at a limiter may rise up to the loop voltage (per flux tube circulation). Electron induced secondary electron emission has no influence at all on these results, which are applied to measured SOL plasma parameters in the TEXTOR tokamak as an example.