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.

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.

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.

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.

Quasi-coherent micro-instabilities is one of the key topics of magnetic confinement fusion. This work focuses on the quasi-coherent spectra of ion temperature gradient (ITG) and trapped-electron-mode instabilities using newly developed far-forward collective scattering measurements within ohmic plasmas in the J-TEXT tokamak. The ITG mode is characterized by frequencies ranging from 30 to 100 kHz and wavenumbers ($k_{\theta}\rho_{\rm s})$ less than 0.3. Beyond a critical plasma density threshold, the ITG mode undergoes a bifurcation, which is marked by a reduction in frequency and an enhancement in amplitude. Concurrently, enhancements in ion energy loss and degradation in confinement are observed. This ground-breaking discovery represents the first instance of direct experimental evidence that establishes a clear link between ITG instability and ion thermal transport.

Tokamak plasmas with elongated cross sections are susceptible to vertical displacement events (VDEs), which can damage the first wall via heat flux or electromagnetic (EM) forces. We present a 3D nonlinear reduced magnetohydrodynamic (MHD) simulation of CFETR plasma during a cold VDE following the thermal quench, focusing on the relationship among the EM force, plasma displacement, and the $n=1$ mode. The dominant mode, identified as $m/n = 2/1$, becomes destabilized when most of the current is contracted within the $q = 2$ surface. The displacement of the plasma current centroid is less than that of the magnetic axis due to the presence of SOL current in the open field line region. Hence, the symmetric component of the induced vacuum vessel current is significantly mitigated. The direction of the sideways force keeps a constant phase approximately compared to the asymmetric component of the vacuum vessel current and the SOL current, which in turn keep in-phase with the dominant $2/1$ mode. Their amplitudes are also closely associated with the growth of the dominant mode. These findings provide insights into potential methods for controlling the phase and amplitude of sideways forces during VDEs in the future.

For warm/hot and dense plasmas (WDPs), ionization potential depression (IPD) plays a crucial role in determining its ionization balance and understanding the resultant microscopic plasma properties. A sophisticated and unified IPD model is necessary to resolve those existing discrepancies between theoretical and experimental results. However, the applicability of those widely used IPD models nowadays is limited, especially for the nonlocal thermodynamic equilibrium (non-LTE) dense plasma produced by short-pulse laser. In this work, we propose an IPD model that considers inelastic atomic processes, in which three-body recombination and collision ionization processes are found to play a crucial role in determining the electron distribution and IPD for a WDP. This IPD model is validated by reproducing latest experimental results of Al plasmas with a wide-range condition of 70 eV–700 eV temperature and $0.2$–$3$ times solid density, as well as a typical non-LTE system of hollow Al ions. It is demonstrated that the present IPD model has a significant temperature dependence due to the consideration of the inelastic collision processes. With a lower computational cost and wider application range of plasma conditions, the proposed model is expected to provide a promising tool to study the ionization balance and the atomic processes, as well as the related radiation and particle transports properties of the WDP.