Analysis of the scrape-off layer plasma in toroidal helical systems

The connection length L between the magnetic field line and the wall in the scrape-off layer (SOL) region in toroidal helical systems is analysed. It is found that this connection length has a logarithmic dependence on the distance from the outermost magnetic surface to the field line under consideration. Using this dependence in a fluid model, the spatial distribution of the plasma in the SOL region is studied analytically. The edge temperature scales approximately as P 0.36 (P being the power flow to the SOL region), as for tokamaks. For a given value of P, the edge temperature in toroidal helical systems is lower than in tokamaks with a similar minor radius.