Search Results (6)

Vacuum arc thrusters (VATs) have recently gained significant interest as a micro-propulsion system due to their scalability, low cost, storability, and small form factor. While VATs offer an attractive propulsion solution for CubeSats, conventional propellant feed systems used in VATs require intricate mechanical moving parts, increasing overall system complexity and mission risk. A promising alternative is the use of VAT arrays, where multiple thin-layer VATs are arranged in a regularly spaced grid, thus enhancing reliability, increasing total impulse without a mechanical propellant feed system, and enabling integrated attitude control via off-axis thruster placement. However, VAT arrays require a larger power processing unit (PPU) and additional control system, posing challenges within CubeSat volume constraints. To address this, this study proposes a novel PPU design that enables the simultaneous operation of multiple VATs while minimising system mass and volume. Experimental results demonstrate the successful operation of VAT pairs using the proposed PPU concept, validating its feasibility as an efficient propulsion solution for CubeSats. Full article

A vacuum arc is an electrical discharge, in which the current is supported by localized cathode heating and plasma generation in minute regions at the cathode surface called cathode spots. Cathode spots produce a metallic plasma jet used in many applications (microelectronics, space thrusters, film deposition, etc.). Nevertheless, the cathode spot is a problematic and unique subject. For a long time, the mechanisms of spot initiation, time development, instability, high mobility, and behavior in magnetic fields have been described by approaches that caused some controversy. These spot characteristics were discussed in numerous publications over many years. The obscurity and confusion of different studies created the impression that the cathode spot is a mysterious phenomenon. In the present work, a number of typical representative publications are reviewed with the intention of clarifying problems and contradictions. Two main theories of cathodic arcs are presented along with an analysis of the experimental data. One of the approaches illustrates the cathode heating by Joule energy dissipation (volume heat source, a sharp rise in current density, etc.), nearly constant cathode potential drop, and other certain initial conditions. On the other hand, a study using a mathematically closed approach shows that the spot initiation and development are determined not by electron emission current rise but by a rise in arc power density, affecting heat sources including the energy of ion flux to the cathode (surface heat source). Full article

Measurements of ion speed in the plume of a pulsed high-current vacuum arc thruster were performed by means of electrostatic probes. The probes were designed to provide direct speed measurements with minimum disturbance on the plasma jet. Typical mean values of $v_i$ for Ti and Cu cathodes are determined at different locations downstream of the electrodes, in the far field region. From one VAT discharge to another, the mean ion speed strongly varies which leads to a large statistical dispersion. Single-shot analysis allows the observation of the plume anisotropy and its high divergence as well as the existence of several ion groups of different speeds throughout a discharge. Full article

In order to support increasingly detailed simulation models in the field of plasma generation and expansion, more experimental data are needed to prove and verify these models. In addition to existing invasive probe methods and spectroscopy, optical diagnostics methods can be employed for this purpose. These can be used to obtain information about the transient behavior of the plasma plume itself. For this purpose, a pseudo stereo imaging system was assembled, which consisted of a biprism and one camera. The presented setup was used to observe the plasma plume expansion of a vacuum arc thruster and to detect how a magnetic nozzle changes the plume expansion behavior of the used thruster. For this, areas were calculated by means of contour detection from both view directions, and a 3D model was reconstructed by computing cross-sectional images. The results show that the magnetic nozzle provides a more uniform formation of the plasma plume, which can be seen by comparing the calculated areas from both directions of observation and is confirmed by the reconstructed 3D models. Thus, the used setup is suitable as an additional diagnostic tool in the future. Despite its simple design, it provides information about the spatial development of a plasma plume. It can serve as a fast and simple verification tool for simulation results, where otherwise complex tomographic setups and reconstructions would be necessary to obtain spatial information. Further measurements are recommended to improve and validate the recording and evaluation process. Full article

In this work, thrust measurements of the high efficient and reliable vacuum arc thruster (HERVAT) are performed for different pulse energies. The thruster system includes a thruster head together with a newly developed pulse processing unit (PPU). The complete system (HERVAT + PPU) is able to perform more than 1 × 10⁷ pulses. Moreover, the influence of an integrated active magnetic nozzle is investigated. As a result, the thrust to power ratio, the average thrust level and the impulse bit for each configuration are measured and calculated. For the thrust measurements, a highly sensitive horizontal thrust balance with an active force actuator is used and operated in the thrust compensation mode. The investigated system is able to achieve levels from 5 to 40 μN and thrust to power ratios from 1 to 2 μN/W. The experimental results are compared to the data available in literature. Full article

Vacuum arc thruster performance in a magnetic nozzle configuration is experimentally characterized. Measurements are performed on a miniature coaxial thruster with an anode inner diameter of $1.8$ mm. The magnetic field B is produced by a single air coil, 18 mm in diameter. Direct measurement of thrust, mass consumption and arc current are performed. To obtain statistically viable results $\approx 6000$ arc pulses are analyzed at each operational point. Cathode mass erosion is measured using laser profilometry. To sustain thruster operation over several measurement cycles, an active cathode feeding system is used. For $0<B\le 0.2$ T, performance increase over the non-magnetic case is observed with the best thrust to arc power ratio $T/P\approx 9$ $\mathsf{\mu }$ N/W obtained at $B\approx 0.2$ T. A parametric model is provided that captures the performance enhancement based on beam collimation and acceleration by the magnetic nozzle. For $B>0.2$ T, the arc discharge is shown to be suppressed nullifying any additional gains by the nozzle effect. Full article