Manufacture of TiO2 nanoparticles with high preparation efficiency and photocatalytic performance by controlling the parameters of pulsed laser ablation in liquid.

This study proposes a method to improve the production efficiency and photocatalytic performance of TiO2 nanoparticles using the pulsed laser ablation in liquid (PLAL) method to optimise preparation parameters. In this study, the variation of particle size, morphology, preparation, and catalytic efficiency due to the increase in the number of pulses is studied. The mechanism of particle morphology change is analysed using thermodynamic simulation. The density functional theory (DFT) is used to calculate and characterise the reason why the special structure formed by particle breaking improves the photocatalytic performance. In addition, the influence of the law of solution height on particle breakage is summarised to obtain an optimised preparation parameter. The proposed method provides a reference for the selection of parameters in actual production.

Ray-tracing analysis for combined Doppler backscattering and cross-polarization scattering diagnostic on the HL-2M tokamak.

To measure plasma density and magnetic fluctuations on the HL-2M tokamak simultaneously, a new diagnostic system combining Doppler backscattering (DBS) and cross-polarization scattering (CPS) is under development. It is essential to understand the propagation of injected and scattered rays to support the electronic/quasi-optical design and subsequent interpretation of the detected signals of the multi-channel DBS/CPS measurements. Thus, ray-tracing analysis with the axisymmetric ray-tracing code BORAY has been performed to estimate the scattering location and wavenumbers of the density and magnetic fluctuations. In addition, the influence of accordance between toroidal and poloidal launch angles is investigated. The received DBS/CPS signal quality can be improved by matching the parallel wavenumber in the direction of magnetic field lines.

Rapid photodegradation of methylene blue by laser-induced plasma.

A new strategy was established for the degradation of wastewater-based organic pollutants. Laser-induced plasma (LIP) was used as an alternative UV light source to realise rapid photodegradation of methylene blue (MB), an organic pollutant. A conventional 1064 nm Nd:YAG laser was used for plasma excitation to degrade MB solutions. The results show that the LIP effectively degraded the organic matter, and the degradation efficiency was related to the UV component with wavelength less than 400 nm. The compositions of the plasma excited by different dielectric substrates are different owing to various mechanisms involving moderate heat dissipation and sonoluminescence. However, metallic substrates, especially Fe, can enhance the proportion of UV light and accelerate the degradation efficiency. In the process of methylene blue degradation, solution parameters, such as initial dye concentration, pH, irradiation time and hydrogen peroxide concentration, will affect the degradation efficiency. The conditions of effective degradation of methylene blue (10 mg L-1 MB-1 concentration, 50 mL L-1 H2O2 concentration, pH = 3 and P = 60 mW) were obtained in this study, which can provide reference for practical application.

Recent advances in high- ß N experiments and magnetohydrodynamic instabilities with hybrid scenarios in the HL-2A Tokamak.

Over the past several years, high- ß N experiments have been carried out on HL-2A. The high- ß N is realized using double transport barriers (DTBs) with hybrid scenarios. A stationary high- ß N ( > 2 ) scenario was obtained by pure neutral-beam injection (NBI) heating. Transient high performance was also achieved, corresponding to ß N ≥ 3 , n e / n e G ∼ 0.6 , H 98 ∼ 1.5 , f b s ∼ 30 % , q 95 ∼ 4.0 , and G ∼ 0.4 . The high- ß N scenario was successfully modeled using integrated simulation codes, that is, the one modeling framework for integrated tasks (OMFIT). In high- ß N plasmas, magnetohydrodynamic (MHD) instabilities are abundant, including low-frequency global MHD oscillation with n = 1, high-frequency coherent mode (HCM) at the edge, and neoclassical tearing mode (NTM) and Alfvénic modes in the core. In some high- ß N discharges, it is observed that the NTMs with m / n = 3 / 2 limit the growth of the plasma energy and decrease ß N . The low-n global MHD oscillation is consistent with the coupling of destabilized internal (m/n = 1/1) and external (m/n = 3/1 or 4/1) modes, and plays a crucial role in triggering the onset of ELMs. Achieving high- ß N on HL-2A suggests that core-edge interplay is key to the plasma confinement enhancement mechanism. Experiments to enhance ß N will contribute to future plasma operation, such as international thermonuclear experimental reactor .

Influences of fusion neutrons on Compton suppressed γ-spectrum analyses at the HL-2A tokamak.

The newly-built Compton suppression system at the HL-2A tokamak works in a harsh fusion neutron field especially when the second neutral beam injection system is put into application. The present paper performed Geant4 simulations to study the influences of fusion neutrons on Compton suppressed γ-spectrum analyses. The simulation data show that the influence of fusion neutrons on suppressed γ-spectrum shape is limited, while the influence on detection efficiencies is considerable. Consequently, the changes of detection efficiencies caused by the coexisting neutrons must be taken into account in the subsequent γ-spectrum analyses. Hence, the empirical formulas of γ-ray detection efficiencies of the Compton suppression system, which had considered the influences of fusion neutrons, were put forward and then applied to unfold the experimental γ-spectra. This work lays a superior foundation for the further analyses of the Compton suppressed γ-spectra at the HL-2A tokamak.

Development of high-speed vacuum ultraviolet spectroscopy using a modified Seya-Namioka monochromator and channel electron multiplier detector in the HL-2A tokamak.

A high-speed vacuum ultraviolet monochromator is developed for the HL-2A tokamak through the introduction of a novel channel electron multiplier in a modified Seya-Namioka spectrometer. A good signal to noise ratio of above 2000 is attained in the development phase of the system with typical operating parameters for observing routine HL-2A plasmas. The wavelength calibration is performed using characteristic line emissions from a hollow cathode light source with helium and argon discharges. The first measurement result of the monochromator at a sample rate of 60 kHz is presented in comparison with the visible Dα signals.

A multiplexer-based multi-channel microwave Doppler backward scattering reflectometer on the HL-2A tokamak.

The Doppler backward scattering (DBS) reflectometer has become a well-established and versatile diagnostic technique for the measurement of density fluctuations and flows in magnetically confined fusion experiments. In this work, a novel multiple fixed-frequency array source with a multiplexer technique is developed and applied in the multi-channel DBS system. The details of the system design and laboratory tests are presented. Preliminary results of Doppler shift frequency spectra measured by the multi-channel DBS reflectometer systems are obtained. Characteristics of plasma rotation and turbulence before and after supersonic molecular beam injection are analyzed.

A novel multi-channel quadrature Doppler backward scattering reflectometer on the HL-2A tokamak.

A novel 16-channel fixed frequency Doppler backward scattering (DBS) reflectometer system has been developed on the HL-2A tokamak. This system is based on the filter-based feedback loop microwave source (FFLMS) technique, which has lower phase noise and lower power variation compared with present tunable frequency generation and comb frequency array generation techniques [J. C. Hillesheim et al. Rev. Sci. Instrum. 80, 083507 (2009) and W. A. Peebles et al. Rev. Sci. Instrum. 81, 10D902 (2010)]. The 16-channel DBS system is comprised of four × four-frequency microwave transmitters and direct quadrature demodulation receivers. The working frequencies are 17-24 GHz and 31-38 GHz with the frequency interval of 1 GHz. They are designed to measure the localized intermediate wave-number (k⊥ρ ∼ 1-2, k⊥ ∼ 2-9 cm-1) density fluctuations and the poloidal rotation velocity profile of turbulence. The details of the system design and laboratory tests are presented. Preliminary results of Doppler spectra measured by the multi-channel DBS reflectometer systems are obtained. The plasma rotation and turbulence distribution during supersonic molecular beam injection are analyzed.