Characteristics of edge temperature ring oscillation during the stationary improved confinement mode in EAST

Abstract

The I-mode is a natural edge localized mode (ELM)-free regime with H-mode-like improved energy confinement and L-mode-like particle confinement, making it an attractive scenario for future tokamak-based fusion reactors. A kind of low-frequency oscillation has been widely observed, with a frequency between stationary zonal flow and geodesic-acoustic mode (GAM) zonal flow. In EAST, most stationary I-mode shots have such a mode, called edge temperature ring oscillation (ETRO). This mode probably plays an important role in development and maintenance of the I-mode , while investigations are needed to clarify the differences between ETRO and similar mode low-frequency oscillation in other devices, such as limit cycle oscillation (LCO). In this paper, the properties of ETRO are described in detail, including the structure of its magnetic components, its radial propagation characteristics, statistics of its central frequency, a linear analysis of the alternating transition turbulences and a comparison with GAM and LCO. Although some similarities can be found between ETRO and both GAM and LCO, the main features are not identical. ETRO is probably a novel type of finite frequency zonal flow or pressure gradient-induced drift that is unique to the I-mode. It is found that modest fueling can reduce ETRO intensity while maintaining I-mode confinement, suggesting that supersonic molecular beam injection could be used as an effective tool to control ETRO.

Experimental and simulation analysis of Weakly Coherent Modes in I-mode discharges on EAST

“…However, this phenomenon is different in EAST. Similar to the phenomenon observed in C-Mod and AUG, a low-frequency toroidal symmetric mode, edge temperature oscillation (ETRO) [16], is present in the I-mode on EAST and has been observed in 90% of the discharges [17]. However, it has been confirmed that ETRO is not GAM [17].…”

“…A mode with a characteristic frequency of approximately 5 Hz is evident in the timefrequency spectrum of the envelope, indicating its modulation of high-frequency density fluctuations. Simultaneously, this mode is observed in other signals, including ECE in the edge (ρ ∼ 0.9), divertor LP, DR, SXR, AXUV, and Mirnov coils [17]. Based on these features, it is identified as the ETRO.…”