[en] Full text of publication follows: Thick tungsten (W) coatings prepared by vacuum plasma spraying (VPS) on copper (Cu) substrate is one of important potential materials for plasma facing components (PFCs) in future tokamaks. In order to investigate the thermal behavior of the coatings under high heat fluxes, W coatings of ∼1 mm thick were deposited onto a directly cooled, movable Cu limiter. And the limiter has then been tested using an e-beam high heat flux (HHF) device and also exposing to HT-7 long pulse plasmas. The limiter can withstand the e-beam irradiation of >20 cycles at duration of 100 s/cycle and heat load of ∼ 10 MW/m². The limiter was exposed to 1 minute plasmas with LHCD power of 130 kW in HT-7 where the surface and bulk temperatures were monitored employing an IR camera and thermocouples, respectively. The heat flux deposited onto the limiter was evaluated by an ANSYS code using the measured surface temperatures as boundary conditions and the heat fluxes have been calculated to be 5- 7 MW/m². And the calculated temperature distribution/evolution inside the limiter have also been compared with those measured by the thermocouples. Results from the coming HT-7 campaigns will also be presented on the conference. (authors)

[en] Highlights: • A control on the magnetic order and phase-transition dynamics by tuning FeRh film thickness was reported. • The decrease of film thicknesses results in an AFM to FM phase change, accompanied by a 0.55% lattice expansion. • Phase transition dynamics are highly dependent on the film thickness. • Phase transition involves in the release and recovery of strain, leading to lower transition temperature in thinner films. • Possible approaches to narrow down the thermal hysteresis are proposed. -- Abstract: The control of magnetic order and phase-transition dynamics by various means is a key towards low-power spintronics. Here, we report a control on magnetic order and phase-transition dynamics by tuning film thickness in epitaxial FeRh films. Reduction of film thicknesses from 200 nm to 5 nm results in an anti-ferromagnetic to ferromagnetic phase change, accompanied by a 0.55% lattice expansion for c-axis. The phase-transition dynamics is highly dependent on the film thickness, and involves the release and recovery of lattice strain that results in a lower transition temperature and larger thermal hysteresis in thinner films. The findings help to understand the origin of thermal hysteresis and phase-transition dynamics in ultra-thin FeRh films. Possible approaches to narrow down thermal hysteresis are proposed.

[en] Tungsten and its alloys have been considered as candidate plasma-facing materials for the EAST tokamak, ITER and future DEMO reactors, due to their favorable properties. A component of W coatings on Cu heat sink prepared by vacuum plasma spraying (VPS), acting as a poloidal movable limiter, has been being tested in the HT-7. During last HT-7 campaign, the W/Cu limiter was subjected to more than 20 similar Ohmic plasmas at different positions, still further exposed to more than 20 long pulse plasmas with durations from 10 to 60 s, driven by low hybrid wave (LHW) of 130 kW. The eroded C and CH particles from the fixed graphite limiters drift and redeposit on the PFM surfaces in the HT-7. It is necessary to understand and predict the PFM surface properties and performance under irradiation of H plasma with C impurities. Atomic scale simulations, that include detailed structure information of the material, are the most attractive tool for understanding such processes. In this work, the calculation is carried out using the classical molecular dynamics (MD) simulation method with a bond-order potential for the ternary W-C-H system. The statistical uncertainties of the MD calculations were kept to be less than one percent. The calculation results are compared qualitatively to the experimental data obtained from visible spectroscopy in the HT-7. By changing the C impurity concentration, target temperature, exposure time and position of the W/Cu limiter inserted into the HT-7 vacuum chamber, the process of chemical erosion of W by carbon coming as a hydrogen plasma impurity to the W surface has been investigated. Simultaneously, the following processes have been studied: ion reflection, CH physisorption and physical sputtering, local atomic composition changes and C concentration changes in the depth profile. Finally, it will be discussed that among above processes which step is crucial for the surface modification and determines the lifetime of W limiter. (authors)

[en] Tungsten materials have been selected as plasma-facing materials for the EAST tokamak in the second phase with increasing the heating and driving powers. A plasma-facing materials and components (PFMC) program to develop W coatings on Cu heat sink is underway at ASIPP, in collaboration with GZRINM. The W coatings are prepared by vacuum plasma spraying (VPS). The W/Cu components have been developed employing a composition gradient interlayer so as to alleviate mismatch of some physical properties between Cu and W. The gradient interlayer shows dense and lamellar microstructure and the coating surface few microcracks. The tensile bond strength of about 21 MPa was achieved with the failure occurring within the coatings, indicating stronger interface. More properties of the coatings and the W/Cu components are to be presented on the workshop, including microstructure, porosity, thermal conductivity, degassing, and trapping and retention under deuterium plasma irradiation. (authors)

[en] The EAST coherent modes (CMs) during the inter-ELM phase are simulated by the electromagnetic six-field two-fluid module in BOUT++ framework. The fluctuation level of the electrostatic potential, electron pressure and density perturbations are comparable to the experiments, and the simulated electrostatic perturbation is around two orders of magnitude larger than the magnetic one in EAST CM. The frequency and poloidal wave number are consistent with experiments in the simulations of EAST CM equilibriums. The energy transfer between three-wave coupling indicates that the energy tends to transfer from medium-n to low-n modes in the early nonlinear phase, and the modes coupling effect in the nonlinear saturation phase is larger than that in the early nonlinear phase. Both the energy transfer and bispectral analysis show that the N _i fluctuation tends to generate the ‘single-mode’ coupling and T _e tends to be ‘multiple-mode’, which indicates that the collapse of the density profile is larger than the electron temperature. The relative phase analysis is applied to evaluate whether the turbulence can extract the energy from density and temperature profiles. The result indicates that the density profile provides much more energy to drive the turbulence than electron temperature. The kinetic and magnetic energy transfer rates are used to understand the instability and turbulence driving mechanisms of the EAST CM. In the linear phase of the nonlinear simulation, the instability is driven by the peeling-ballooning mode and drift-Alfven wave (DAW), and the radial electric field and shear Alfven wave have large suppressing effects. The turbulence of EAST CM is a predominantly electrostatic mode, which corresponds to the Reynolds stress seven times larger than Maxwell stress. In addition, the effect of the electrostatic part in DAW is much larger than the electromagnetic one. (paper)

[en] Magnetic vortices are characterized by the sense of in-plane magnetization chirality and by the polarity of the vortex core. Searching for efficient ways to control the vortex polarity and chirality is of highly fundamental and practical significance towards high speed and high density non-volatile memory applications. Here we report a novel vortex core (VC) switching process in a notched disk, driven by a pulse field. Micromagnetic simulations demonstrate that the dynamics of edge solitons around the notch play a critical role in the switching process, that leads to a sub-nanosecond VC fast switching. The switching diagram as a function of the field strength and duration was presented to indicate the operational range. Further studies on the VC switching under an out-of-plane bias field demonstrate that such switching is deterministic and robust against magnetic environment. Finally, by applying a resonant alternative field, a periodic VC switching is observed with much reduced switching field. The presented results indicate the potential of notched disks for VC based memory applications.