Study of turbulence in the high betap discharge using only RF heating on EAST

High poloidal beta scenarios with favorable energy confinement (β_p~1.9, H_98y2~1.4) have been achieved on Experimental Advanced Superconducting Tokamak (EAST) using only radio frequency waves heating. Gyrokinetic simulations are carried out with experimental plasma parameters and tokamak equilibrium data of a typical high β_p discharge by the GTC code. Linear simulations show that electron temperature scale length and electron density scale length destabilize the turbulence, collision effects stabilize the turbulence, and the instability propagates in the electron diamagnetic direction. These indicate that the dominant instability in the core of high β_p plasma is collisionless trapped electron mode. Ion thermal diffusivities calculated by nonlinear gyrokinetic simulations are consistent with the experimental value, in which the electron collision effects play an important role. Further analyses show that instabilities with k_θ ρ_s>0.38 are suppressed by collision effects and collision effects reduce the radial correlation length of turbulence, resulting in the suppression of the turbulence.

Through-Plane and In-Plane Thermal Diffusivity Determination of Graphene Nanoplatelets by Photothermal Beam Deflection Spectrometry

In this work, in-plane and through-plane thermal diffusivities and conductivities of a freestanding sheet of graphene nanoplatelets are determined using photothermal beam deflection spectrometry. Two experimental methods were employed in order to observe the effect of load pressures on the thermal diffusivity and conductivity of the materials. The in-plane thermal diffusivity was determined by the use of a slope method supported by a new theoretical model, whereas the through-plane thermal diffusivity was determined by a frequency scan method in which the obtained data were processed with a specifically developed least-squares data processing algorithm. On the basis of the determined values, the in-plane and through-plane thermal conductivities and their dependences on the values of thermal diffusivity were found. The results show a significant difference in the character of thermal parameter dependence between the two methods. In the case of the in-plane configuration of the experimental setup, the thermal conductivity decreases with the increase in thermal diffusivity, whereas with the through-plane variant, the thermal conductivity increases with an increase in thermal diffusivity for the whole range of the loading pressure used. This behavior is due to the dependence of heat propagation on changes introduced in the graphene nano-platelets structure by compression.

Algorithms for thermal diffusivity measurement of heterogeneous 1D materials based on Infrared Microscopy Enhanced Angstrom Method

An infrared microscopy enhanced Angstrom method has been develpoed to measure the thermal diffusivity. Infrared microscopy technique can acquire temperatures of multiple points at one shot. Two algorithms for calculating thermal diffusivity were proposed and compared in practice. One is based on global temperature data and the other is based on local temperature data. The according calculated thermal diffusivities are denoted as α n G and α n L . Three 1D materials of different heterogeneity (Cu wire, Ni-Cu wire and PVA-CNT fiber) were measured on the experimental platform. The calculated α n G and α n L values show that for homogeneous material such as Cu, these two algorithms give similar results, while for heterogeneous ones (Ni-Cu and PVA-CNT), they come to be discrepant. The data fluctuation analysis of f n L zooms in the discrepancy and verifies that α n L is more sensitive to local property change and more competent in revealing heterogeneous properties.

Green Constructing an Intelligent Temperature-Regulating Fabric with Multiple Heat-Transfer Capabilities

Textiles with heat management function have good effects on improving human comfort during sport. However, it is still a great challenge to endow textiles with responsiveness to external environmental changes. Herein, we developed an intelligent temperature-regulating cotton textile with multiple heat transfer capability by a two-step method. Firstly, hydroxylated boron nitride (BN-OH) nanosheet dispersion liquid was prepared using a two-step ultrasonic-alkali treatment. Subsequently, enzymatic graft polymerization of N-isopropyl acrylamide (NIPAM) onto cotton fibers were performed using horseradish peroxidase (HRP). The composite cotton fabric, containing entrapped BN-OH exhibits unique temperature-regulating ability, and the thermal diffusivities in vertical and parallel directions reach 1.2 and 1.7 times of the untreated, respectively. This can be attributed to the temperature responsiveness of poly-NIPAM (PNIPAM) and the increase in the packing density of the thermal conductive nanosheets at high temperatures. Meanwhile, the PNIPAM covering the fiber surfaces slowly expands at low temperatures, accordingly minishes the gap sizes between fabric yarns and endows the fabric with improved heat preservation effects. The present work provides a facile and green strategy for developing the intelligent textiles with ambient temperature self-response ability.

The Thermal Diffusivity of Glass Sieves: II. Gas-saturated Frits

The thermal diffusivity of gas-saturated glass sieves (frits) of porosities between 20 % and 48 % is presented as measured at room temperature and ambient pressure. The saturants cover a range in thermal diffusivity from 20.63 × 10–6 m2⋅s−1 to 172 × 10–6 m2⋅s−1. The experiments were carried out using a transient hot-bridge instrument of an expanded uncertainty of 5 % to 10 %. It turned out that all measured thermal diffusivities of the gas-saturated frits (1) are smaller than that of the borosilicate glass the frits are made from and (2) are completely different from the thermal diffusivities of the liquid-saturated frits. Both these discrepancies can be attributed to characteristic properties of the matrix and not directly to the saturants. The first divergence results from thermal tortuosity that lengthens the pathway of heat through the matrix, whereas the second arises from dissolved He that enhances the transport of heat through the matrix.