Abstract
A quasiperiodic Er oscillation at a frequency of , much lower than the geodesic-acoustic-mode frequency, with a modulation in edge turbulence preceding and following the low-to-high () confinement mode transition, has been observed for the first time in the EAST tokamak, using two toroidally separated reciprocating probes. Just prior to the transition, the Er oscillation often evolves into intermittent negative Er spikes. The low-frequency Er oscillation, as well as the Er spikes, is strongly correlated with the turbulence-driven Reynolds stress, thus providing first evidence of the role of the zonal flows in the transition at marginal input power. These new findings not only shed light on the underlying physics mechanism for the transition, but also have significant implications for ITER operations close to the transition threshold power.
- Received 19 May 2011
DOI:https://doi.org/10.1103/PhysRevLett.107.125001
© 2011 American Physical Society