The project investigated the extraction and acceleration of ions from a microwave‑driven plasma source for use in a future space propulsion concept. A plasma generation component was operated at 20 W of microwave power with an argon gas flow of 20 sccm. Three electrodes were used: a plate electrode (PE), grid 1 (G1) and grid 2 (G2). The grids were made of a transparent material with 40 % open area, consisting of 5 mm diameter holes over a 40 mm length. All electrodes could be biased independently up to –300 V through a 1 kΩ series resistor, allowing the current to be measured from the voltage drop across the resistor. A probe system enabled variable biasing up to –140 V while simultaneously recording the resulting current.

When all three electrodes were connected to the same negative potential, the extracted ion current increased with the applied voltage, but saturation had not yet been reached at the maximum tested voltage of –140 V. The measured current reached approximately 0.3 mA, demonstrating that ions can be extracted through a transparent electrode. The plate electrode alone already captured a large fraction of the current, suggesting that a significant portion of ions recombines on the walls of the expansion chamber or that the effective electric field at the distant grids is weakened. The combined configuration of PE, G1 and G2 produced the highest current, indicating that the extraction geometry strongly influences performance.

Systematic scans of the extraction voltage, gas flow and microwave power were performed. With all electrodes biased at –300 V, increasing the gas flow from 10 to 30 sccm raised the current from roughly 0.15 mA to 0.35 mA, while raising the microwave power from 10 to 30 W increased the current from about 0.12 mA to 0.28 mA. These results confirm that both plasma density and extraction field strength are critical parameters. Future work will focus on optimizing the electrode geometry, particularly the position and transparency of the extraction grid, to maximize ion throughput while minimizing losses to chamber walls.

Optical diagnostics were implemented using cameras mounted on two viewport windows of the vacuum chamber. One camera viewed the plasma generation region axially, while the other observed the expansion chamber laterally, allowing visual confirmation of plasma stability and plume shape during operation.

The research was carried out within a German national research framework, involving a consortium of universities and research institutes. While the specific partners and funding agency are not detailed in the provided text, the project aligns with national priorities for advanced propulsion technologies and is expected to contribute to the development of a Microwave Cyclotron Resonance Plasma Thruster (MCPT). The consortium’s collaborative effort combined expertise in plasma physics, electrode design, and diagnostic instrumentation, with the project timeline spanning several experimental phases from initial electrode testing to parameter optimization and concept validation.