Yanan Wang

The magnetic nozzle plasma thruster, as an electrode-less and grid-less electric propulsion system, has received widespread attention in recent years for its simple system and quasi-neutral extraction characteristics. However, due to its relatively simplistic magnetic field configuration, it is difficult to balance high-efficiency discharge and excellent ejection performance. Therefore, a novel microwave magnetron plasma thruster is proposed, which utilizes permanent magnet arrays to construct a magnetic field to simultaneously satisfies both electron confinement and plasma extraction conditions. Then, a series of diagnostic tests are conducted to investigate the performance of thruster. The diagnostic results show that the plasma density in the discharge chamber can reach 1×1017/m³, and indicate that an ion core forms in bulk plasma to eject ions and attract electrons. The thrust test results show that under the conditions of 5 sccm xenon flow rate and 30W input microwave power (or 15 sccm N2 flow rate and 36W input microwave power), the measured thrust is about 1.1 mN. The study can provide a new kind of design method and experimental data for developing plasma thruster systems.

The transient ignition process of Hall thrusters generates pulse current surges with amplitudes tens of times higher than the steady-state discharge current, posing significant challenges to power supply systems and electrode reliability. However, in conventional thrusters, direct observation of internal plasma dynamics is hindered by the obstruction of discharge channel walls, and existing particle-in-cell (PIC) simulation results lack experimental validation, leading to bottlenecks in elucidating the spatiotemporal evolution of plasma parameters and developing surge current suppression strategies. In this study, an open-structured external-discharge Hall thruster is employed to achieve direct visualization of plasma channel dynamics during ignition for the first time. By integrating high-speed ICCD imaging, PIC-Monte Carlo collision simulations, and transient circuit modeling, the regulatory mechanisms of anode voltage and propellant mass flow rate on plasma parameters and current surges are investigated. Experimental results demonstrate that increasing the anode voltage from 180 V to 240 V accelerates electron energy accumulation (up to 55 eV), elevates the pulse current peak from 1.49 A to 2.96 A, and reduces the ignition duration by 40%. When the propellant flow rate rises from 0.3 mg s ⁻¹ to 0.7 mg s ⁻¹ , the neutral atom density increases to 1.8 × 10 ²¹ m ⁻³ , significantly enhancing ionization rates and driving the current peak to 3.68 A. Key phenomena, including dual-ionization-zone coordinated discharge and axial plume expansion, are experimentally validated. Furthermore, a dynamic plasma impedance model is established to propose staged voltage initiation and graded flow regulation strategies, which reduce the electrical stress factor from 10.84 to 2.27. These findings overcome the limitations of traditional diagnostic methods and model validation, providing theoretical insights and engineering guidelines for designing high-reliability Hall thrusters and optimizing power system redundancy.

Underwater pulsed discharges are pivotal for research fields like acoustic wave generation and material processing, where improving energy efficiency and achieving precise parametric control are critical objectives. However, the performance of electrohydraulic discharge load faces challenges including large breakdown delay and jitter, complex multi-physical coupling, etc. Here, an underwater surface load utilizes carbon-foil triple-junction (TJ) points to trigger kV-level discharges and pressure waves. The optimized load offers key advantages: largely-reduced electric breakdown delay and phenomenal reproducibility in repetitive operation. This study systematically investigates the effects of current density, load length, and stored energy on discharge characteristics, acoustic performance, and bubble pulsation. Results show that increasing foil length from 5 mm to 20 mm (at 2 J) elevates the voltage peak from 0.93 kV to 1.37 kV and improves energy deposition efficiency from 1.47 J to 1.85 J. Furthermore, the acoustic performance is highly controllable: peak pressure rises with stored energy, reaching up to 43.1 kPa (corresponding to a sound pressure level of approximately 212.7 dB re 1 μPa @ 20 cm), while the discharge pressure waveform before material failure is closer to a strong shock wave. Additionally, four distinct bubble regimes are identified in varied tests: merged double bubbles, non-merging double bubbles, triple bubbles, and multi-bubbles. These findings may deepen the understanding of underwater discharge physics and demonstrate its advantages in related applications.

This study investigates the evolution of transient arc plasma and its ablation behavior of cathode (initial) material under high-power electric pulse, addressing the issue of material ablation control arising from localized thermal gradients and phase transitions during plasma-condensed-matter interactions. Experiments were conducted using a pin-plate gas gap breakdown at varying ambient pressures. The discharge process was diagnosed using synchronized high-speed photography and voltage/current/photoelectric probes. Following discharge channel formation, plasma expansion was observed with an initial velocity of 2–3 km s⁻¹, evolving from a spherical shape into an inverted bell shape, subsequently contracting into an inverted funnel configuration, accompanied by the plasma ejection in form of electrode spots. Increasing the discharge current from 15.4 kA to 21.9 kA resulted in a ∼90% increase in plasma radiation intensity. Reducing the ambient pressure led to increased dispersion and weakened radiation intensity of the plasma channel. Post-discharge ablation morphology observations revealed concentrated ablation with distinct regions at 0.1 MPa. Pressure, contrasting with a speckle pattern and significantly reduced surface roughness (R _a decreasing from ∼2.5 μm to < 0.5 μm) at lower pressure of 0.02 MPa. Inspired by these findings, the study explored and validated the arc-root dispersion effect and ablation homogenization capability of metal foams.