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In a reversed shear discharge in the Experimental Advanced Superconducting Tokamak (EAST), an internal transport barrier (ITB) was formed. For the first time, the turbulence in the plasma core before and after the formation of the ITB in EAST was investigated by microwave reflectometry. It was found that during the formation of the ITB, the turbulence inside the barrier was not completely suppressed. The density fluctuation level decreased in the early phase of ITB and significantly increased later. It was found that the density fluctuation level increased with the density gradient after the appearance of reversed shear Alfvén eigenmodes (RSAEs). The change in turbulence, measurable by the reflectometer, did not affect the rate of increase in core density. Through the measurement of RSAEs, it was found that the formation of this ITB may be related to the minimum q (q min). q min was close to 2.

The extraordinary mode (X-mode) lower cut-off frequency is proposed for use in the reflectometry diagnostic on ITER for the electron density profile measurement, which is a trade-off between extreme plasma parameters and the accessible probing frequency. In contemporary experiments, the lower cut-off frequency can be identified at the probing frequency below the electron cyclotron frequency (f ce) under certain plasma conditions. We provide here, for the first time, the experimental validation of the use of the lower cut-off frequency for the density profiles via the reflectometry measurement on EAST. The corresponding group delay of the lower cut-off frequency evolves continuously with the upper one, revealing a reasonable radial coverage extension of reflectometry measurement toward the plasma core. It is concluded that the lower cut-off frequency can be used as a supplement to the upper one in the density profile inversion process, which is of particular interest in the high magnetic field and/or density discharge to extend the radial coverage of reflectometry measurement.

Chinese fusion engineering test reactor (CFETR) is under conceptual design to bridge gaps between ITER and DEMO. CFETR is envisioned to produce a 200 MW (200 MW in phase I and will be increased to 1-GW level) fusion power with tritium breeding ratio >1 and a duty cycle time of approximately 0.3–0.5. This paper is to present the status in the conceptual design of CFETR diagnostic system. Based on the experience obtained in the development of ITER diagnostics and combined with CFETR special requirements, progress of CFETR diagnostic system has been described. They mainly includes: 1) the conditions and constraints in CFETR environment and 2) one set of proposed measurements and candidate diagnostic techniques for CFETR phase I. The possible needed R&D activities for future work are under review. Two R&D examples under progress will be introduced.

Simultaneous control of the damaging erosion induced by the transient and steady-state heat/particle fluxes on the divertor target material is one of the critical issues for next-step magnetic fusion devices. H-mode operation without large edge-localized modes has been achieved in EAST with an ITER-like tungsten divertor, while being compatible with the partial and pronounced detachment in divertor, via either ramping-up of bulk density or injection of low/high-Z impurities. The pedestal characteristics during the transition from the attached to the detached divertor and the reversed transition (detached to attached) under different detachment methods are studied in detail, where the evolution of multi fluctuating structures commonly residing in the H-mode pedestal of EAST (edge coherent mode (ECM), magnetic coherent mode (MCM) and high frequency mode (HFM)) is highlighted. In addition, the possible mechanisms that affect the behavior of these modes, such as the pedestal pressure gradient and the collisionality, have also been discussed. The radial structures of ECM, MCM and HFM are detected, for the first time, in one discharge. Relevant research may provide contribution to obtaining an integrated small/no ELM and radiative divertor scenario in the next step.

An eight-channel poloidal correlation reflectometer (PCR) with O-mode polarization has been installed in the EAST tokamak to measure the fluctuations from core to edge. The PCR launches eight different frequency microwaves (20.4, 24.8, 33, 40, 42.4, 48, 52.6, 57.2 GHz) into the plasma from the low field side and two poloidally separated antennae are used to receive the reflected waves. As a result, the diagnostic can measure fluctuations in eight (radial)× two (poloidal) spatial positions. The diagnostic has been applied to study the core and edge pedestal fluctuations during an inter-ELM phase in H-mode plasma. This inter-ELM phase can be divided into two stages. In the first stage, a low frequency (

A cross-scale interaction between a kink instability with toroidal mode number (n) of 1 and background microturbulence (mainly a coherent mode with n = 12–17) has been observed in the H-mode edge pedestal region in the EAST tokamak. The n = 1 kink mode with a frequency ~3.5 kHz is localized in the pedestal region. The amplitude of pedestal microturbulence is evidently modulated at the frequency of the n = 1 mode. This amplitude modulation is mainly for the fluctuation component with frequency less than 100 kHz, while no modulation by the n = 1 mode is observed for the component with frequency larger than 100 kHz. This implies that the observed amplitude modulation by the n = 1 mode is not due to the Doppler shift effect. A further analysis shows that the amplitude modulation of microturbulence could be attributed to modulation of the local temperature gradient by the n = 1 kink mode. In addition, bicoherence analysis indicates that there exists a possible direct nonlinear interaction between background microturbulence and the n = 1 kink instability. A preliminary analysis shows that this cross-scale interaction has no evident effect on the pedestal structure.