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The edge turbulence characteristics and the induced radial transport have been investigated in edge localized mode (ELM) suppression by using the $n = $ 4 resonant magnetic perturbation coils on EAST, with ${q_{95}} = $ 3.6 and the electron collisionality $\nu _{\text{e}}^* \approx $ 0.5. During ELM suppression, the edge turbulence is enhanced dramatically, as measured by the reciprocating probe and the poloidal correlation reflectometry. In the near SOL, the low frequency turbulence (250 kHz), which could be beneficial to form the observed turbulent transport. The estimated upstream cross-field particle flux is consistent with the total particle flux deposited on divertor targets, demonstrating that the enhanced radial turbulent particle transport is an important mechanism for particle exhaust in ELM suppression.

A newly developed radial directional electron probe (DEP) has been applied to the unidirectional electron current measurement on EAST tokamak. The DEP consists of two radial arrays of channels which have opposite directions and align along the local magnetic field line. Each radial array has 6 holes with a radial interval of 5 mm. Every channel has a hole with 0.5 mm radial width, 3 mm depth and 15° poloidal opening angle. The graphite collector embedded inside the hole is biased to positive potential to repel low energy ions, and high energy ions are blocked by the hole surface because their Larmor radii are larger than the radial width of hole. In consequence, the ion current collected by the DEP collector can be ignored in contrast with the electron current, as demonstrated by the I-V characteristics in a DEP commissioning experiment. The difference of collected current between two opposite channels signifies the unidirectional electron current in the flux tube. In a lower hybrid wave (LHW) modulation experiment, the amplitude and radial structure of unidirectional electron current induced by LHW is measured directly by this radial DEP array, and the LHW filament current covers over 20 mm radial region with a maximum of 20 A/cm2.

Experiments in EAST have concentrated on studying the internal transport barrier (ITB) regime in high normalized beta () discharges, where the study of the compatibility between ITB dynamics and divertor plasmas is an important step for future steady-state and high-performance plasma operations. In this work, the characteristics of the divertor particle flux and their responses to ITB dynamics have been studied in high- discharges. In order to describe the characteristics, the ITB duration is divided into two phases: phase I (i.e. ITB formation) and phase II (i.e. ITB degradation), according to the variation of plasma stored energy. In phase I, the particle flux near the inner strike point (SP) is continuously enhanced during the inter-edge-localized mode (ELM) phase in both the lower single-null and upper single-null configurations. The total particle flux in the scrape-off layer (SOL) region reveals a similar trend with an increase of the flux near the SP. However, in the private flux region (PFR) the total particle flux shows a reduction. Meanwhile, a movement of the SP away from the divertor corner is also observed during the ITB formation. In phase II, the particle flux near the inner SP, the total particle flux in the inner SOL and PFR region recover to their initial level before ITB formation, respectively. Additionally, the particle decay length is obviously reduced in phase I and then gradually enhanced in phase II. The continuous variation of the particle flux at the inner divertor target is in accordance with a compression of the magnetic flux surfaces due to ITB formation, which increases the gradient of electron density in the edge region. It is indicative that the ITB has a feasible impact on the behavior of divertor plasmas by means of increasing the Shafranov shift during the inter-ELM phase. [ABSTRACT FROM AUTHOR]

Characteristics of the pressure-driven magnetohydrodynamic (MHD) instabilities in the magnetic stochastic region, which surrounds the core plasma of the large helical device, are studied. There appear MHD instabilities with an amplitude of 10−4of the toroidal magnetic field. From the mode number of activities (poloidal/toroidal mode number , 1/2, 2/4), the location of the corresponding rational surface is near the LCFS or definitely outside the LCFS. Parameter dependence of the saturation level is examined for evaluation of the impact of MHD activities. The saturation level increases with increase of the pressure gradient and decreases with decrease of the local collisionality. In order to study the dependence on the magnetic field structure, experiments with the resonant magnetic field perturbation (RMP) with m/n = 1/1 were conducted. While the magnetic island is formed around the rotational transform surface, the magnetic field structure outside the nested region is disturbed. Amplitude of m/n = 2/3 and 2/4 modes are reduced by this resonant magnetic pertubation (RMP) field when the normalized RMP coil current exceeds 0.3 kA T−1. Since the local pressure gradient and the local plasma parameters are not changed by the RMP, this reduction is caused by the change of the magnetic field structure itself. [ABSTRACT FROM AUTHOR]