Electric propulsion devices of using xenon propellant are nowadays widely adopted for the space missions. A collisional-radiative (CR) model of xenon needs to be developed to understand the kinetic mechanisms of the excited and energetic species in these devices and also to support their optical diagnostics. Previously, due to limitations in the fundamental cross section data, Xe CR models focused on the atomic species; the ionic species, which also play important roles for the thrusters, were not studied in detail. In our previous paper, a fully relativistic Dirac B -spline R -matrix method was applied to calculate the relevant cross sections for electron collisions with the Xe ⁺ ion. Based on these data, a comprehensive CR model—with the kinetics of metastable and excited levels of both Xe and Xe ⁺ included—could be built. The calculated density distributions of atomic and ionic levels are examined by optical measurements in Hall thrusters in all of the four typical regions (near-anode-, ionization-, acceleration-, and plume-region). The special kinetic behaviors of the excited species are analyzed, and a set of rate coefficient data used for the Xe CR model is also provided.

A fully relativistic Dirac B-spline R-matrix (DBSR) method is applied to calculate the oscillator strengths and electron-impact excitation cross sections involving the 5s ² 5p ⁵ , 5s5p ⁶ , 5p ⁴ 6s, 5p ⁴ 5d, 5p ⁴ 6p, and 5p ⁴ 7s states of a Xe ⁺ ion. A fully relativistic approach is necessary for this problem, since the spin–orbit coupling is of the same order as electron correlations in the outer shells of Xe ⁺ . Also, there is a complex open-shell structure with strong term dependence in the one-electron orbitals. The oscillator strengths are also calculated and agree well with available experimental measurements. We select some important excitation cross sections out of the ground, metastable, and quasi-metastable states of Xe ⁺ for the collisional-radiative (CR) model to be discussed and analyzed. The present paper is the first one of a series of studies on a CR model of xenon ions in plasma diagnosis and numerical simulations of Hall and ion thrusters. In subsequent papers, the cross-section data for the Xe ⁺ ion, together with those for neutral Xe from our previous calculation, are used to build a comprehensive CR model for electric propulsion systems involving xenon. Furthermore, the predictions of this model will then be examined by experiments in both Hall and ion thrusters.

Ammonia as a non-carbon fuel is expected to play an important role in the future, but it is difficult to be effectively utilized at this stage due to its flame retardancy and other characteristics. Therefore, we propose to use gliding arc plasma combined with a swirl burner to enhance the combustion performance of ammonia. The electrical characteristics, electron density, gas rotational temperature and the distribution of key active species in the burner were studied via optical emission spectroscopy (OES). With the increase of equivalence ratio (EQR), the width of the H_α line decreases significantly, indicating that the electron density shows a downward trend, even as the gas rotational temperature shows an upward trend. When the equivalence ratio was 0.5, the gas rotational temperature increases by about 320 K compared with the pure air condition. During pure air discharge, there will still be obvious NO emission due to the plasma reaction, but with the addition of NH₃, the NO content in the emission is significantly reduced. The light intensity of O atoms in the burner gradually decreases with the increase of the equivalence ratio, the light intensity of H atoms increases first and then decreases, and the light intensity of NH shows an upward trend. The reason may be that the plasma discharge effectively strengthens NH₃(E)->NH₂+H, NH₂+H->NH+H₂ and other reactions promote the initial reaction step of NH₃ which thus effectively strengthens the NH₃ combustion.

The ionization fraction is a key figure of merit for optimizing the performance of plasma device. This work presents an optical emission spectroscopy (OES) method to determine the ionization fraction in low-temperature xenon plasma. The emission line-ratio of xenon ionic and atomic 6p–6s transitions is used in this method. A comprehensive collisional-radiative model developed in our previous work is employed to describe the relationship between the line-ratios and the plasma parameters. It is found that some special line-ratios have a sensitive relationship to the ionization fraction, e.g. the ratio of the 460.30 nm line and 828.01 nm lines. These line-ratios are selected for the diagnostic method. The method is demonstrated in a magnetized discharge chamber. The axially-resolved emission spectra of the ionization chamber are measured, and from those the ionization fraction along the chamber axis is determined via the OES method. The axially-resolved ionization fraction is found to be dependent on the magnetic field and agrees well with those obtained from a Langmuir probe. In the experiment, the probe is overheated under some conditions, possibly due to the bombardment by energetic particles. In this case, no results can be obtained from the probe, while the OES method can still obtain reasonable results. Combined with optical tomography and spectral imaging technology, the OES method can also provide the spatial distribution of the ionization fraction, which is needed for revealing the discharge mechanisms of plasma devices.

Space-borne gravitational wave (GW) detection spacecraft works in the state of drag free for which a disturbance reduction system is utilized to offset the non-conservative force. The key actuator of drag-free control loop is a micro-thruster with the performance of a high precision thrust and wide-range operations. Ion thruster, such as electron cyclotron resonance ion thruster (ECRIT), is one of the options because its thrust can be controlled precisely by the method of beam current feedback. However, there is still a barrier for the conventional ECRIT to achieve the low thrust of 1 μN as required in space-borne GWs detection missions due to its radial structure. In this work, a minimized ECR ion thruster (mini-ECRIT) is designed by a new idea that it employs an axial ring-cusped field to exploit the low-pressure adaptability of resonance heating. The mini-ECRIT is tested and results in a dynamic thrust range of 1–100 μN, a resolution of 0.1 μN, a thrust noise of 0.1 μN/Hz^1/2, and a response time of about 10 ms. In addition, the specific impulse of this thruster can reach as high as 510 s at low thrust 5 μN, being higher than that of previous ion thrusters by a factor of about 5, which may significantly reduce the propellant consumption. This minimized ECR ion thruster may support China’s space-borne GW detection missions such as TianQin.