The influence of bremsstrahlung and cyclotron radiation on the evolution and saturation of the m/n = 2/1 resistive tearing mode is investigated by using a three-dimensional toroidal magnetohydrodynamic code. It is found that accumulation of impurities (such as tungsten) in magnetic islands has a destabilizing effect on the tearing mode due to an imbalance of local radiative cooling and Ohmic heating inside the island. The asymmetry current effect and the nonlinear mode coupling play an important role on evolution of the radiation-driven tearing mode instability. As a result, the magnetic island width could increase over 20% of the minor radius (disruption scale). Along with higher mode burst, multi-mode interaction makes magnetic field lines become stochastic. Moreover, the core pressure is reduced due to the radiation cooling inside the magnetic island. Consequently, the whole discharge area is shifted towards the high-field side, which leads to a strong intensification of the m/n = 1/0 mode.

The effects of plasma radiation on the nonlinear evolution of neo-classical tearing modes are investigated based on a set of reduced magnetohydrodynamic (MHD) equations. It is found that the radiation can reduce the pressure near the rational surface. During the nonlinear evolution, the magnitude of perturbed bootstrap current is drastically enhanced in the presence of the radiation. Besides, the radiation can increase the growth rate of the magnetic islands by diminishing the pressure, such that the magnetic islands do not saturate compared with that without radiation. On the other hand, with the increase of the ratio of parallel to perpendicular transport coefficient χ∥/ χ⊥, the reduction of pressure can further increase the growth rate of magnetic islands in the presence of plasma radiation. Finally, the mechanisms of the destabilizing effects driven by the radiation are discussed in detail as well.

We investigate the role of thermal conductivity on the evolution and saturation of the m/n= 2/1 resistive tearing mode (m and n are, respectively, the poloidal and toroidal Fourier mode numbers), by using a 3D toroidal MHD code (CLT). It is found that thermal conductivity has great influence on pressure and current profiles, and further affects the dynamic evolution of the tearing mode. Our simulation results indicate that the linear growth rate of the tearing mode increases, but the saturation level of magnetic islands decreases with increase of thermal conductivity. With a small thermal conductivity, a flattened distribution of the thermal pressure inside magnetic islands leads to a large pressure gradient at the edge that drives a ballooning mode to be unstable. We further found that the radial electric field at the magnetic island boundary and the vortex-like flow inside the magnetic island lead to a poloidally asymmetric transport barrier and reduce the thermal conductivity at the magnetic island boundary, which contributes to formation of an internal transport barrier.

Radio frequency capacitively coupled plasmas (RF CCPs) play a pivotal role in various applications ranging from etching and deposition processes on microscopic scales in semiconductor manufacturing. During the discharge processes, the plasma series resonance (PSR) effect is easily observed in electrically asymmetric and geometrically asymmetric discharges, which could largely influence the power absorption, ionization rate, etc. In this work, the PSR effect arising from geometrically and electrically asymmetric discharges in argon-oxygen mixture gas is mainly investigated by using a plasma equivalent circuit model coupled with a global model. At relatively low pressure, as the Ar content (α) is increasing, the inductance of the bulk is weakened, which leads to a more obvious PSR phenomenon and a higher resonance frequency (w psr). When the Ar content is fixed, varying the pressure and gap distance could also have different effects on the PSR effect. With the increase of the pressure, the PSR frequency shifts towards the higher order, but in the case of much higher pressure, the PSR oscillation would be strongly damped by frequent electron and neutral collisions. With the increase of the gap distance, the PSR frequency becomes lower. In addition, electrically asymmetric waveforms applied to a geometrically asymmetric chamber may weaken or enhance the asymmetry of the discharge and regulate the PSR effect. In this work, the Ar/O2 electronegative mixture gas is introduced in a capacitive discharge to study the PSR effect under GAE and EAE, which can provide necessary guidance in laboratory research and current applications.