In this study, a code, named Peking University Helicon Discharge (PHD), which can simulate helicon discharge processes under both a background magnetic field greater than 500 G and a pressure less than 1 Pa, is developed. In the code, two fluid equations are used. The PHD simulations led to two important findings: (1) the temporal evolution of plasma density with the background magnetic field exhibits a second rapid increase (termed as the second density jump), similar to the transition of modes in helicon plasmas; (2) in the presence of a magnetic field, the peak positions of electron power absorption appeared near the central axis, unlike in the case of no magnetic field. These results may lead to an enhanced understanding of the discharge mechanism.

The helicon wave plasma (HWP) sources have well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies on mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge (PHD) code. The mode transitions also known as density jumps of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude SHWs are responsible for the mode transitions, similar to those of a resonant cavity for laser generation. This paper intends to give a complete and quantitative standing helicon wave (SHW) resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.

A helicon wave plasma (HWP) discharge with strong magnetic field was investigated. The HWP was produced with an internal Nagoya III antenna that is perpendicular to the magnetic field and driven by a 13.56 MHz radio-frequency (RF) source. HWP was characterized in terms of electron density, electron temperature and plasma potential using a single Langmuir probe in Ar gas. The result of Langmuir probe shows that the electron density increases with RF power, but saturate above 700 W at a density of 2×1019m-3. Scanning electron microscopy (SEM) was extensively used to characterize the quality of the graphite surface. The result of SEM shows the surface of graphite that exposed to plasma processing has exhibited smoother and compacter surface topography. Meanwhile, the concentration of impurity on the graphite surface decreases with plasma processing.

In this work, a newly integrated fluid simulation platform, named DUT-HTFS, is developed for the multiple physical fields in Hall thrusters. The integrated simulation platform includes three inter-related parts: the geometry module, background magnetic field module, and plasma module. Using the geometry module, three sets of meshes for a Hall thruster are obtained. One set of the mesh is for the calculation of the background magnetic fields, the second is for the electric potentials, and the third is for the plasmas. Based on the meshes and using the background magnetic field module, a numerical result of the background magnetic field in the Hall thruster is obtained and discussed. Based on the meshes and the numerical result of the background magnetic field, using the plasma module, the numerical results of the plasmas in the Hall thruster are obtained. The results of the plasma density, the electric field, the electric potential, and the ionization rate are similar to those from HPHALL (Hybrid-PIC Hall thruster code) simulations and are qualitatively consistent with the experimental results from the literature. Furthermore, varying the neutral gas pressure from 0.02 to 0.03 Torr, the numerical results of the plasmas in the Hall thruster are obtained. These results reveal that neutral gas pressure effects contributed considerably to the shape, location, and magnitude of the peak plasma properties, including the ion density, axial electric field, and ionization rate. This fluid simulation platform could provide a new angle of view for better understanding of the physical mechanism in Hall thrusters.

The plasma window is a windowless vacuum sealing device that utilizes a cascade arc discharge to isolate regions with different pressures. It was proposed as an alternative to the traditional windowless sealing technology of differential pumping, which greatly improves the sealing efficiency and has been successfully applied in electron beam welding. The discharge channel of the existing plasma window is a small circular hole, referred to as a zero-dimensional plasma window, which has limited applications to its dimensions. In this study, we suggested a one-dimensional (1D) plasma window with a slit discharge channel (cross section: 3 × 35 mm2, length: 60 mm). An arc discharge is realized with the support of an 80 A DC power supply, which can maintain a pressure drop of more than 10 times between the high-pressure and low-pressure ends of the plasma window. A COMSOL-based magneto-hydrodynamic model of the plasma window was established, and simulations were in good agreement with the experimental results. The pressure drop in the plasma window caused by argon plasma has also been theoretically analyzed and discussed. The feasibility of a 1D plasma window to achieve vacuum isolation was verified theoretically, numerically, and experimentally.