Thermoelectric instability in externally induced asymmetric divertor plasmas

The thermoelectric instability in divertor tokamaks has been studied, takin g account of the divertor asymmetry induced externally by the biasing and r ecycling asymmetry. The equilibrium and stability of scrape-off layer ( SOL ) and divertor plasmas are investigated by using a five-point model. In the case of low divertor radiation, there exists a stable equilibrium. On the other hand, in the case of high radiation, there are one unstable and two s table equilibria. The thermoelectric instability arises at the unstable equ ilibrium where the SOL current is small. When the externally induced asymme try is large, one of the stable equilibria only remains and the other equil ibria disappear. At the remaining equilibrium, the SOL current increases wi th the externally induced asymmetry and the thermoelectric instability does not arise.