Onset condition of thermoelectric instability in divertor tokamaks

The onset condition of a thermoelectric instability in divertor tokamaks ha s been studied analytically anti numerically by using a five point model ba sed on SOL and divertor plasmas. The SOL current due to the thermoelectric effect causes the thermoelectric instability and destabilizes the symmetric equilibrium of the SOL and divertor plasmas below a critical divertor plas ma temperature. The critical temperature of the thermoelectric instability is equal to or higher than that of the thermal instability due to the diver tor radiation, and depends on the midplane SOL plasma temperature and the d ivertor radiation loss. Below the critical temperature, stable asymmetric e quilibria are obtained. As the degree of the asymmetry in the divertor plas ma temperature increases, the SOL current has no effect on the instability, or even stabilizes the equilibrium. The SOL current generates spontaneousl y the divertor asymmetry through the thermoelectric instability.