Jinyue Geng

Systematic experimental characterization of the electron extraction characteristics of a radio-frequency plasma bridge neutralizer (RPN) in the actual ion-plume environment of a radio-frequency ion thruster (RIT) remains limited, particularly regarding the effects of ion-beam conditions and the relative configuration between the RIT and RPN. In this study, an experiment consisting of an RIT-13 and an RPN-2.5 was established, in which the RIT-13 operated with an Xe + N₂ + O₂ mixed propellant and the RPN-2.5 operated with Xe. Experimental investigations were conducted to systematically examine the effects of collector bias voltage, ion beam current, screen-grid voltage, RPN installation angle, and spatial position on electron extraction. The results show that the collector bias voltage is the primary parameter governing the electron extraction state, and two distinct jumps occur as the magnitude of the negative collector bias voltage increases, while the ion beam current mainly modulates the electron extraction state near the threshold of the first jump. The 60° and 90° configurations generally exhibit stronger electron extraction capability than the 0° and 30° configurations and require smaller magnitudes of negative collector bias voltage to reach the high-current electron extraction state. A pronounced spatial dependence is also observed. At an ion beam current of approximately 440 mA and a screen-grid voltage of 1200 V, the region of X = −10 mm and Y = 20–40 mm exhibits favorable electron extraction characteristics. Among the investigated configurations, the 90° configuration at (−10, 40) mm requires the smallest magnitude of collector bias voltage, approximately 13.5–14 V, for the RPN electron extraction current to match the RIT ion beam current. This current-matching bias is defined in the present study as the equivalent floating potential U_eq. These results provide an experimental basis for the matching design and spatial configuration of RITs and RPNs in an air-breathing electric propulsion system.

Molybdenum (Mo), owing to its excellent high-temperature resistance and low sputtering yield, is widely used in advanced equipment such as extreme ultraviolet (EUV) lithography systems. To meet the demand for regulating the surface wettability of Mo, this study employs micromilling to fabricate microgroove arrays on Mo surfaces to enhance their hydrophobicity. First, comparative micromilling experiments are conducted under flood cooling and minimum quantity cooling lubrication (MQCL) conditions. The effects of process parameters, including axial depth of cut (a_p), spindle speed (n), and feed per tooth (f_z), on burr height (H) are investigated under the two cooling/lubrication conditions. The results show that the burr heights obtained under flood cooling are generally lower than those obtained under MQCL. Subsequently, the machining parameters under flood cooling are evaluated using an orthogonal experimental design. A mathematical model relating the microgroove array geometry to the contact angle is then established based on Gibbs free energy to guide the design of surface microgroove structures. Finally, microgroove arrays are fabricated on Mo surfaces using the preferred machining parameters. The results demonstrate that the microgroove arrays effectively enhance the water hydrophobicity of the Mo surface. The static water contact angle increases from 62.45 ± 0.25° for the untreated Mo surface to a maximum of 128.50 ± 0.12°, thereby achieving a transition from hydrophilic to hydrophobic behavior.

Molybdenum (Mo), owing to its excellent properties, is widely used as a plasma-facing material and is recognized as a typical difficult-to-machine material. Achieving high-quality, low-damage machining is essential for ensuring the service reliability of Mo components. However, studies on the milling of Mo remain limited. Therefore, this study investigates a high-quality, low-damage milling technique for Mo based on analyses of milling force, machined surface roughness, and white layer formation. First, the effects of machining parameters, including radial depth of cut (a_e), spindle speed (n), and feed per tooth (f_z), on the responses, namely milling force (F) and surface roughness (R_a), were investigated. The relationships between milling force, surface roughness, and white layer formation were analyzed. Subsequently, the response surface methodology (RSM) was employed to reveal the influence mechanisms of the machining parameters and their interactions on the response variables. Finally, a Kriging surrogate model integrated with the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was adopted to identify the optimal machining parameter combination for high-quality, low-damage milling. The results indicate that the milling force and white-layer thickness exhibit consistent increasing trends with increasing feed per tooth under the investigated conditions, demonstrating that controlling the milling force is an effective approach for achieving high-quality, low-damage milling of Mo. For the simultaneous minimization of milling force and surface roughness, the optimal machining parameters were determined to be a radial depth of cut of 0.2101 mm, a spindle speed of 10,090.7 rpm, and a feed per tooth of 0.01 mm/z. These findings provide valuable process parameter guidance for the precision machining of Mo components.

Very low Earth orbit (VLEO) satellites are confronted with the challenge of orbital decay caused by thin atmospheres, and the volume and power limitations of micro satellites further restrict the application of traditional electric propulsion systems. In response to the above requirements, this study proposes an innovative scheme of radio frequency plasma micro-thrusters based on magnetic nozzle acceleration technology. By optimizing the magnetic nozzle configuration through the system, the plasma confinement efficiency was significantly enhanced. Combined with the mixed working medium (5 sccm Xe + 10 sccm air), the thrust reached 1.7 mN at a power of 130 W. Experiments show that the configuration of the magnetic nozzle directly affects the plasma beam morphology and ionization efficiency, and a multi-magnet layout can form a stable trumpet-shaped plume. The air in the mixed working medium has a linear relationship with the thrust gain (60 μN/sccm), but xenon gas is required as a “seed” to maintain the discharge stability. The optimized magnetic nozzle enables the thruster to achieve both high thrust density (13.1 μN/W) and working medium adaptability at a power level of hundreds of watts. This research provides a low-cost and miniaturized propulsion solution for very low Earth orbit satellites. Its magnetic nozzle-hybrid propellant collaborative mechanism holds significant engineering significance for the development of air-aspirating electric propulsion technology.

Very-low Earth orbit (VLEO) space below 200 km is essential for high-quality communications and near-Earth space environment detection. Due to the significant atmospheric drag, orbital maintenance is required for spacecraft staying here. Based on air-breathing electric propulsion (ABEP) technology, this paper analyzed the orbital boundary conditions of the spacecraft under the constraints of parameters including slenderness ratio, thrust-to-power ratio, drag coefficient, and effective specific impulse. The energy balance is the key constraint for low VLEO orbits, which is determined by the drag coefficient, slenderness ratio, and thrust-to-power ratio. Under the existing technical conditions, the lowest circular orbit (along the terminator) is about 170 km. An elliptical orbital flight scheme is also analyzed to reach a 150 km perigee. A half-period control method was proposed based on the on–off control method for the elliptical orbit, which could enable the spacecraft to maintain a stable 150–250 km elliptical orbit.