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The inward particle flux associated with the global long-lived mode (LLM) during the L–I–H transition on HL-2A tokamak has been measured. The inward particle flux arises from the phase change between density and radial velocity fluctuations, where density and velocity fluctuations are strongly correlated with magnetic fluctuations of LLM. Moreover, the radial velocity and its gradient rather than poloidal flow shear play an important role in particle transport associated with the large-scale mode. The strong nonlinear coupling between LLM and ambient turbulence has been confirmed, and this may contribute to most of the inward particle flux in the LLM during the I-phase state.

We report about the soft X-ray (SXR) tomography system which is being developed on Keda Torus eXperiment (KTX). The tomographic system aims at studying three dimensional effects in reversed field pinch with high plasma current, particularly in quasi-single-helicity state (QSH). The view distribution of the probes has been carefully designed to reflect the experimental constraints. Bayesian experimental design (BED) is used to optimize the signal camera location and camera opening angle, aiming at maximizing the gain information in future QSH states. The BED approach allows us to quantitatively evaluate the performance of the design, and to estimate the design robustness. The physical image of the plasma is tomographically reconstructed using Cormack approach and the reconstructed emissivity image may be compared to the emissivity model using the residual error χ. The camera location, camera opening angle, and sightline density are finally decided by quantitatively comparing diverse designs in order to achieve the best reconstruction.

A poloidal and toroidal magnetic field coupling circuit model is developed to simulate discharge waveforms of the Keda Torus eXperiment (KTX) reversed field pinch (RFP) to ensure that the design of the power supply systems is able to achieve the typical discharge parameters. The radial profiles of plasma current density and magnetic field used in the coupling model are characterized by modified Bessel function model (MBFM) derived from the well-known Taylor's theory. The power balance in the energy conservation of poloidal and toroidal fields is used to establish the connection between these two fields. The numerical solutions of the coupling show that the KTX power supply system is capable of achieving the designed discharge parameters, such as field reversal parameter ( F ), pinch parameter (Θ), magnetic field, plasma current and loop voltage. Furthermore, the delay of magnetic field penetration due to the effect of vacuum vessel is also considered in the model.

The Keda Torus eXperiment (KTX) is still operated in the commissioning phase, and preparation for the operation capability of the KTX phase II upgrade is underway. The diagnostics in the KTX have been greatly developed: (1) the terahertz interferometer has been upgraded to seven chords for electron density profile inversion; (2) a Thomson scattering system with a 5 Joule laser has been installed and commissioning is in progress; (3) a 3D movable probe system has been developed for the electromagnetic turbulence measurement; (4) double-foil soft x-ray imaging diagnostics have been set up and a bench test has been completed; (5) an edge capacitive probe has been installed for the radial electrical field measurement; (6) a multi-channel spectrograph system has been built for detecting impurities of carbon and oxygen. In addition, the design of a new compact torus injection system has been completed for feeding and momentum driving. Pilot research, such as the 3D reversed field pinch physics and electromagnetic turbulence, etc, have been conducted in the discharge status of the KTX. The 3D spectra characters of electromagnetic turbulence are firstly measured using a classical two-point technique by Langmuir probe arrays set on the 3D movable probe system and edge magnetic sensors. The forward scattering is collected by the interferometer system, which shows the potential for turbulence research. The electromagnetic turbulence is tentatively investigated in the KTX. The formation of a quasi-single-helicity state in the KTX regime is also preliminarily explored in simulation.