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The active control of internal transport barriers (ITBs) is an important issue to achieve high performance plasma in a fusion reactor. A critical challenge of ITB control is to increase the ITB position. The ITBs with internal kink modes (IKMs), such as fishbone (FB) instability and long-live mode (LLM) with mode number of m / n = 1/1 are frequently observed on HL-2A tokamak in neutral beam heated discharges. The correlation of FB instability/LLM with ITBs is analyzed in order to extend the ITB radius. It has been revealed that FB instability and LLM are often excited after the ITB formation. Therefore, FB instability and LLM play no role in triggering ITBs on HL-2A tokamak. On the other hand, they may slow down the outward radial expansion and then shrink the foot position of ITB, and damp the gradient growth of ion temperature and rotation velocity. Since the perturbation of LLM is weaker than that of FB instability, the shrinking effect of ITB foot and braking effect on gradient growth are slighter than those of FB instability. Compared with the LLM, FB instability routinely appears in plasmas with lower density, higher heating power and lower plasma current. In addition, large ITBs without IKMs are also discussed on HL-2A tokamak. The large ITB is the largest one, the FB ITB is the strongest one and the LLM ITB is the widest one in three ITBs, where the ‘large’, ‘strong’ and ‘wide’ qualifications correspond to ITB position ρ ITB, the normalized temperature gradient R /LT, and its width W / a. Therefore, the large ITB position may be obtained if the IKMs are effectively controlled in a tokamak. [ABSTRACT FROM AUTHOR]

$Z_{\mathrm {eff}}$ is measured by two visible bremsstrahlung diagnostics on HL-2A tokamak, one of which uses a high spectral resolution spectrometer coupled with an electron multiplied CCD (temporal resolution of 100 Hz), and the other uses a filterscope system (temporal resolution of 1 MHz). The bremsstrahlung brightness measured by them coincides with each other very well. $\bar {Z}_{\mathbf {eff}}$ is systematically measured under different discharge conditions, such as divertor and limiter configurations, ohmic and auxiliary heating phases, before and after siliconization, and $L$ – $H$ transition. Under ohmic phase, $\bar {Z}_{\mathbf {eff}}$ is higher in the limiter configuration than that in the divertor configuration by a factor of ~1.5 under high-density regime. $\bar {Z}_{\mathbf {eff}}$ increases in all cases of auxiliary heating scenarios due to enhanced plasma–wall interaction, accompanied by influx increases of low ionization states of impurities such as C2+ and Fe1+ in plasma edge. Siliconization for wall conditioning is prominently effective in lowering the main impurity influxes in plasma edge and thus the impurity level, and a concentration of ~4% for carbon and ~0.2% for iron is roughly evaluated for a typical nonsiliconized plasma. A simple relationship that $Z_{\mathrm {eff}}$ is positively correlated with $\Phi _{\mathrm {in}}$ and $\tau _{\mathrm {p}}$ is verified from the L- and $H$ -mode features, where $\Phi _{\mathrm {in}}$ is the impurity influx and $\tau _{\mathrm {p}}$ the particle confinement time. A nearly constant $\bar {Z}_{\mathbf {eff}}$ evolution is observed during $L$ – $H$ and $H$ – $L$ transition and it seems that $\bar {Z}_{\mathbf {eff}}$ is insensitive to $L$ – $H$ and $H$ – $L$ transition under some $Z_{\mathrm {eff}}$ (0) threshold. The $Z_{\mathrm {eff}}$ profiles are flat/weakly hollow in plasma core region (rho < 0.7) in case of low $Z_{\mathrm {eff}}$ (0) and tend to be peaked when $Z_{\mathrm {eff}}$ (0) is larger than 3, which agrees with the neoclassical theory prediction. [ABSTRACT FROM AUTHOR]

The Napahai plateau wetland, located in northwestern Yunnan province, China, is a unique seasonal plateau wetland of low-latitude and high-altitude, yet the microbial community is still unknown. To address this shortcoming, MiSeq high-throughput sequencing was used to analyze the composition and diversity of bacteria and archaea. The bacterial community comprised of 64 phyla, 164 classes and 484 genera, in which Proteobacteria was the most abundant, followed by Actinobacteria, Chloroflexi and Acidobacteria. Archaea comprised of 3 phyla, 5 classes, and 7 genera, in which Thaumarchaeota dominated. The results indicated that the composition and diversity of the bacterial community were more influenced by seasonal changes than by soil types, whereas the archaeal community was mostly resistant to these factors. Additionally, canonical correlation analysis (CCA) showed that the diversity of the bacterial community was closely correlated with nitrogen (N), total nitrogen (TN) and soil organic matter (SOM) in the dry season. However, no significant correlation of any of the factors was observed in the archaeal community. In conclusion, these results indicated that microbial communities in the soil of Napahai plateau wetland have unique diversity and composition, and Napahai plateau wetland as a microbial resource requires protection and restoration. [ABSTRACT FROM AUTHOR]