Resistive X-point modes in tokamak boundary plasmas

It is shown that the boundary (edge and scrape-off-layer) plasma in a typic al low (L) mode diverted tokamak discharge is unstable to a new class of mo des called resistive X-point (RX) modes. The RX mode is a type of resistive ballooning mode that exploits a synergism between resistivity and the magn etic geometry of the X-point region. The RX modes are shown to give robust instabilities at moderate mode numbers, and therefore are expected to be th e dominant contributors to turbulent diffusion in the boundary plasma of a diverted tokamak. (C) 2000 American Institute of Physics. [S1070-664X(00)03 206-7].