A new mechanism for the high-Z impurity neoclassical particle transport in the tokamak plasmas due to the single-null divertor configuration is discovered for the first time. It will play an important role in the tokamak plasma pedestal region with the coexisting of the strong bulk ion radial gradients and the up/down asymmetry of the poloidal magnetic field. The outward (inward) high-Z impurity neoclassical particle transport will be driven with the drift towards (away from) the X-point. The new finding indicates that the International Thermonuclear Experimental Reactor lower single-null divertor configuration will be beneficial for screening and flushing out the high-Z impurity in the pedestal region with the toroidal magnetic field in the normal direction ( drift towards the X-point).
This paper discovers a new mechanism for the high-Z impurity transport in tokamak plasmas with a single-null divertor configuration. It shows that the up/down asymmetry of the poloidal magnetic field can drive outward or inward transport of high-Z impurities, which is important for the plasma pedestal region. This finding suggests that the ITER's lower single-null divertor can help screen and flush out high-Z impurities.