부산대학교 도서관

The sawtooth oscillation, observed in tokamak plasmas with a central safety factor of less than unity, is a periodic disruptive instability characterized by a slow ramping of central plasma density and temperature, followed by a fast relaxation resulting in flattening of both profiles. Elongated neutral-beam-heated discharges on the DIII-D tokamak exhibit multiple precursor oscillations with mode number $m/n = 1/1$. The dominant $m/n = 1/1$ mode oscillates at the plasma rotation frequency. A downshifted mode also appears early in the sawtooth ramp. A normalization of electron cyclotron emission imaging data that removes the contribution of slow electron temperature profile evolution reveals that both modes are consistent with an underlying quasi-interchange plasma displacement.