Density edge localized modes in rotating plasmas

A linear analysis is presented for the density edge localized mode with realistic tokamak edge plasma and electric field profiles. The mode is driven unstable by the electron temperature gradient and is localized by the density pedestal, with a radial mode width proportional to the square root of the density scale length (in H mode). The mode persists under the observed levels of sheared plasma rotation because of its narrow radial width. Its mode frequency, growth time, poloidal mode number and direction of rotation are all found to be comparable with those of the precursors for small (type III) edge localized modes (ELMs) observed in DIII-D and ASDEX. It is concluded that the density edge localized mode is a promising candidate for the precursors