Limit-cycle-oscillation induced from the positive feedback amplification of radial electric field in the scrape-off-layer

Abstract

Based on a heuristic model of the scrape-off-layer (SOL) plasma dynamics, a new type of limit-cycle-oscillation (LCO) is shown to be possible in the SOL region. The key trigger process is the positive feedback amplification of the SOL radial electric field through the SOL turbulence suppression and temperature profile steepening. This SOL-LCO can make the edge plasma inside the separatrix also have an oscillation motion, taking the features qualitatively similar to those observed in the recent ASDEX Upgrade experiment (Cavedon et al 2017 Nucl. Fusion 57 014002). With the above positive feedback process much more feasible when the ion magnetic curvature drift direction is toward the X -point, the present model also provides an explanation of why the LCO is mostly observed in such a favorable magnetic configuration.

Keywords

• limit-cycle-oscillation
• L-H transition
• scrape-off-layer
• H-mode