Observation of Pedestal Plasma Turbulence on EAST Tokamak

Abstract

Pedestal plasma turbulence was experimentally studied by microwave reflectometry on EAST tokamak. The characteristics of edge pedestal turbulence during dithering L-H transition, ELM-free H-mode phase and inter-ELM phase have recently been studied on EAST. An edge spatial structure of density fluctuation and its dithering temporal evolution is observed for the first time on the EAST tokamak during the L-H transition phase. A coherent mode usually appears during the ELM-free phase prior to the first ELM on EAST tokamak. The mode frequency gradually decreases as the pedestal evolves. Analysis shows that the coherent mode is in the pedestal region inside the separatrix. In plasma with type-III ELMs, a precursor mode before ELM is usually observed. The frequency of the precursor was initially about 150 kHz and gradually decreased till the next ELM. The mode amplitude increases or shows saturation before ELM. In the plasma with compound ELMs composed of high and low frequency ELMs, the precursor was also observed before the high frequency ELM while the harmonic oscillations with frequencies of 20 kHz, 40 kHz and 60 kHz appear before the low frequency ELM.

Linear gyrokinetic investigation of the geodesic acoustic modes in realistic tokamak configurations

“…Although the Gao 2010 theory provides considerably smaller damping rate, it seems to give similar trend of the damping coefficient with the plasma elongation, i.e., the damping rate is weakened by the elongation. The Gao 2010 theory was derived in the large orbit drift width limit, where the dominant damping mechanism is the resonance ω ∼ ω d (here, ω d = k r · v d is a magnetic drift frequency, k r is a wave vector of the zonal potential in the radial direction and v d is a magnetic drift velocity) [35]. As explained in Ref.…”

Experimental study of pedestal turbulence on EAST tokamak

“…In previous studies, [22,23], a CM is usually observed in the ELM-free period after transition to H-mode in the lower hybrid wave (LHW) dominated heating plasmas (e.g. figure 4 in [22]).…”

“…In previous studies, [22,23], a CM is usually observed in the ELM-free period after transition to H-mode in the lower hybrid wave (LHW) dominated heating plasmas (e.g. figure 4 in [22]). The CM is usually born at a frequency of approximately 80-100 kHz and then gradually chirps down to approximately 40-50 kHz in the fluctuation spectrum measured by reflectometry in the pedestal region.…”

“…Over the past several years, abundant turbulence modes in the edge pedestal region [22,23] have been observed mainly by using reflectometry in the EAST tokamak. In the ELM-free phase just after the L-H transition, a CM has been observed in the pedestal region in lower hybrid wave (LHW) dominated heating H-mode plasma.…”

Three-Dimensional Inhomogeneity of Electron-Temperature-Gradient Turbulence in the Edge of Tokamak Plasmas

“…These turbulent fluxes constrain the pedestal's magnetohydrodynamic stability [30][31][32][33][34], neoclassical transport [35], and scrape-off-layer processes [36]. Extensive experimental, numerical, and analytic results suggest that iontemperature-gradient (ITG) [3,37,38], ETG [4,39], microtearing [40], kinetic-ballooning [41,42], and trappedelectron modes [43] are responsible for anomalous heat losses in the pedestal [26,[44][45][46][47][48][49][50][51][52][53][54][55][56]. Pedestal instability and turbulence peaking away from the outboard midplane has been observed for ETG [57][58][59], ITG [60], microtearing [48,53,61], and trapped-electron modes [61].…”