Potassium niobate (KNbO3) microcubes with orthorhombic and tetragonal phases were hydrothermally prepared and characterized by powder X-ray diffraction, nitrogen adsorption-desorption, micro-Raman spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance UV-visible spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The photoreactivity of the as-prepared KNbO3 samples was evaluated regarding the hydrogen evolution from aqueous methanol under UV, and the results were compared with that of cubic KNbO3 microcubes. The photocatalytic reactivity was shown to be phase-dependent, following the order cubic > orthorhombic > tetragonal. Insight into the phase-dependent photocatalytic properties was gained by first-principles density functional calculations. The best photocatalytic performance of cubic KNbO3 is ascribed to it having the highest symmetry in the bulk structure and associated unique electronic structure. Further, the surface electronic structure plays a key role leading to the discrepancy in photoreactivity between orthorhombic and tetragonal KNbO3. The results from this study are potentially applicable to a range of perovskite-type mixed metal oxides useful in water splitting as well as other areas of heterogeneous photocatalysis.

Blob statistical characteristics across the separatrix of HL-2A tokamak plasma have been studied using a reciprocating Langmuir five-probe array. The radial profile of inverse pressure gradient scale length has a maximum just inside the last closed flux surface (LCFS), where the skewness is close to zero. Conditional average reveals that the density holes and blobs are produced just inside the LCFS and they propagate in opposite directions. The poloidal velocity of blobs changes its sign when it is across the separatrix, which is consistent with E × B drift flow. The dramatic change in phase shift between density and potential fluctuations across the separatrix suggests the distinct properties of turbulence when the magnetic field line changes from a closed to an open one. The dependence of a weak three-wave interaction in terms of wavelet bicoherence on strong time-asymmetry blobs is observed for the first time. Moreover, the effective blob generation rate is estimated as 8.0 × 10 3 s −1 and the convective particle flux induced by the ejective blobs can lead to about 58% loss of radial particle flux.

Beta-induced Alfvén eigenmode (BAE) during a strong tearing mode activity (termed as m-BAE) has been observed and investigated in HL-2A. BAE excited by energetic electrons (termed as e-BAE) has been identified both in the Ohmic and ECRH plasma. The hard x-ray spectrum detected by cadmium telluride and the non-thermal radiation measured by electron cyclotron emission are used to analyse the behaviour of the energetic electrons. Experimental results show that the e-BAE is related not only to the populations of the energetic electrons, but also their energy distribution. An interesting result about the BAEs modulated by a supersonic molecular beam and gas puffing is presented. In addition, BAEs during a sawtooth cycle are described in this paper. To assess the identification of the e-BAE and m-BAE, the generalized fishbone-like dispersion relation and magnetic-island-induced BAE dispersion relation are solved near marginal stability, respectively. Compared with experimental results, the calculation analysis shows that the observed frequencies are all close to the theoretical results.

The β-induced Alfvén eigenmode (BAE) excited by energetic electrons has been identified for the first time both in the Ohmic and electron cyclotron resonance heating plasma in HL-2A. The features of the instability, including its frequency, mode number, and propagation direction, can be observed by magnetic pickup probes. The mode frequency is comparable to that of the continuum accumulation point of the lowest frequency gap induced by the shear Alfvén continuous spectrum due to finite β effect, and it is proportional to Alfvén velocity at thermal ion β held constant. The experimental results show that the BAE is related not only with the population of the energetic electrons, but also their energy and pitch angles. The results indicate that the barely circulating and deeply trapped electrons play an important role in the mode excitation.

Strong burst of the internal kink mode has been observed during ECRH on the HL-2A. It has been experimentally identified that the energetic electrons, which deviate from Maxwell velocity distribution, excite the mode, which was so called electron fishbone (e-fishbone). The energy distribution of the electrons is indirectly measured by a hard X-ray detector (CdTe) with the pulse height analysis (PHA).When the counts of the energetic electrons with 35-70keV increase to a higher level, the mode can be observed obviously. The e-fishbone can be excited during off -axis ECRH deposited both the high field side and low field side. The modes propagate toroidally parallel to the precession velocity of deeply trapped ions which is in the same direction as the plasma current (co-current) and poloidally parallel to the electron diamagnetic drift velocity. In order to further identify with e-fishbone mode, the resonance condition of wave-particle has been investigated. Comparing with experimental results, the calculation analyses show that the mode frequency is close to the precession frequency of the barely trapped electrons (BTEs) or the barely circulating electrons (BCEs) when the magnetic shear is very weak or negative.