We report the laser-chirp controlled terahertz (THz) wave generation from two-color-laser-induced air plasma. Our experimental results reveal that the THz wave is affected by both the laser energy and chirp, leading to radiation minima that can be quantitatively reconstructed using the linear-dipole-array model. The phase difference between the two colors, determined by the chirp and intensity of the laser, can account for the radiation minima. Furthermore, we observe an asynchronous variation in the generated THz spectrum, which suggests a THz frequency-dependent phase matching between the laser pulse and THz wave. These results highlight the importance of laser chirp during the THz wave generation and demonstrate the possibility of modulating the THz yields and spectrum through chirping the incident laser pulse. This work can provide valuable insights into the mechanism of plasma-based THz wave generation and offer a unique means to control THz emissions.

Plasma technology has widespread applications in many fields, whereas the methods for manipulating plasma transport are limited to magnetic control. In this study, we used a simplified diffusion-migration approach to describe plasma transport. The feasibility of the transformation theory for plasma transport was demonstrated. As potential applications, we designed three model devices capable of cloaking, concentrating, and rotating plasmas without disturbing the density profile of plasmas in the background. This research may help advance plasma technology in practical fields, such as medicine and chemistry.

A branch of high-frequency Alfvénic modes is observed on the HL-2A tokamak. The electromagnetic mode can be driven unstably in the plasma with an off-axis neutral beam heating. Its mode frequency keeps almost unchanged or presents a slow-sweeping behavior, depending on the detail current evolution. The poloidal and toroidal mode numbers are $m/n=1/1$. The mode has a quite short duration ($\leq$20 ms) and usually appears 5–10 ms after the neutral beam being injected into the plasma. Hybrid simulations based on M3D-K have also been carried out. The result suggests that co-passing energetic particles are responsible for the mode excitation. The simulated mode structures are localized nearby location of minimum safety factor ($q_{\rm min}$) and agree with the structures obtained through tomography of soft x-ray arrays. Further, the modes are localized in the continuum gap and their frequencies increase with variation of $q_{\rm min}$ in a wide range. Last but not least, the characteristic of unchanged frequency on experiment is also reproduced by the nonlinear simulation with a fixed safety factor. All those evidences indicate that the $n=1$ high-frequency mode may belong to a reversed shear Alfvén eigenmode.

Low-temperature synthesis of Nb$_3$Sn thin-film cavity is of great significance in the field of superconducting radio frequency (SRF). The bronze process can grow only stable Nb$_3$Sn phase at 700 ℃, so it is considered to be the most promising process for low-temperature synthesis of Nb$_3$Sn thin-film cavity. We successfully fabricated the worldwide first Nb$_3$Sn thin-film cavity by bronze process. We technically solved the key problems of precursor preparation, characterized and analyzed the uniformity of the Nb$_3$Sn film, and tested the performance of the cut-out samples and the whole cavity of the Nb$_3$Sn film. It is obtained that the $Q_0$ value of the cavity at 4.2 K is about $1.2\times10^{9}$, which is greater than the performance of the bulk-niobium cavity under the same conditions. This result means that the preparation of Nb$_3$Sn by bronze process has the great potential to more practical copper-based Nb$_3$Sn thin-film cavity, which is expected to achieve a substantial improvement in the performance of SRF cavity and comprehensive engineering applications.

The scaling law of divertor heat flux width is one of the key topics of magnetic confinement fusion, which is almost inversely proportional to the poloidal magnetic field on some opened divertor tokamaks. This work focuses on the scaling laws of the closed divertor heat flux width in the HL-2A tokamak under different discharge conditions, such as the Ohmic, L- and H-modes. The results indicate that there are basic similarities of the scaling laws of the heat flux width between the opened and closed divertors. However, a larger spreading width in the private flux region is found, which is relevant to a small expansion factor of the magnetic flux in the closed divertor.

Numerical research is conducted to investigate the effects of plasma boundary shape on the tearing mode triggering explosive bursts in toroidal tokamak plasmas. In this work, $m/n=2/1$ mode is responsible for the triggering of the explosive burst. Plasma boundary shape can be adjusted via the adjustment of the parameters triangularity ${\delta}$ and elongation ${\kappa}$. The investigations are conducted both under low $\beta$ (close to zero) and under finite $\beta$ regimes. In the low $\beta$ regime, triangularity and elongation both have stabilizing effect on the explosive burst, and the stabilizing effect of elongation is stronger. Under a large elongation (${\kappa =2.0}$), the elongation effect can evidently enhance the stabilizing effect in a positive triangularity regime, but barely affects the stabilizing effect in a negative triangularity regime. In the finite $\beta$ regime, the explosive burst is delayed in comparison with that in the low $\beta$ regime. Similar to the low $\beta$ cases, the effects of triangularity and elongation both are stabilizing. Under a large elongation (${\kappa =2.0}$), the elongation effect can evidently enhance the stabilizing effect on the explosive burst in a positive triangularity regime, but impair the stabilizing effect in a negative triangularity regime. The explosive burst disappears in the large triangularity case (${\delta =0.5}$), indicating that the explosive burst can be effectively prevented in experiments via carefully adjusting plasma boundary shape. Moreover, strong magnetic stochasticity appears in the negative triangularity case during the nonlinear phase.

Microturbulence excited by ion temperature gradient (ITG)-dominant and trapped electron mode (TEM)-dominant instabilities is investigated by employing an extended fluid code (ExFC) based on the so-called Landau fluid model, which includes the trapped electron dynamics. Firstly, the global effect is emphasized through direct comparison of ITG and TEM instability domains based on local and global simulations. The global effect makes differences in both linear instability and nonlinear transport, including the fluxes and the structure of zonal flow. The transitions among ITG, TEM, and ITG & TEM (ITG & TEM represents that ITG and TEM coexist with different wavelengths) instabilities/turbulence depend not only on the three key drive forces $({R/L_{\rm n}, R/L_{\rm Te}, R/L_{\rm Ti}})$ but also on their global (profile) effects. Secondly, a lot of electrostatic linear gyro-fluid simulations are concluded to obtain a distribution of the instability.

Machine learning opens up new possibilities for research of plasma confinement. Specifically, models constructed using machine learning algorithms may effectively simplify the simulation process. Previous first-principles simulations could provide physics-based transport information, but not fast enough for real-time applications or plasma control. To address this issue, this study proposes SExFC, a surrogate model of the Gyro-Landau Extended Fluid Code (ExFC). As an extended version of our previous model ExFC-NN, SExFC can capture more features of transport driven by the ion temperature gradient mode and trapped electron mode, using an extended database initially generated with ExFC simulations. In addition to predicting the dominant instability, radially averaged fluxes and radial profiles of fluxes, the well-trained SExFC may also be suitable for physics-based rapid predictions that can be considered in real-time plasma control systems in the future.