Far-Field Beam Diagnostics at DLR’s EP Test Facility

Kurzfassung

With a facility based on a large vacuum chamber of 12m length and 5m diameter the German Aerospace Center DLR in Göttingen performs testing on space electric propulsion systems. This large chamber size gives the option for plasma plume measurements at a long distance, e.g. beyond 5m, compared to the usually employed distance of 0.5-1m. The beam shape and properties at such long distances is of importance for plume-spacecraft interaction and for a space debris removal technique that is based on momentum transfer by ion beams. The goal of the investigation presented here was to measure the divergence of the beam of our radiofrequency ion thruster RIT10/37 at a distance greater 3m. The system has been named LDBS (long distance beam scanner), and in designing the system we selected an x-y-scanner working in a flat plane. This is a complement to rotational systems working at 0.7-1.5m. Actuation of the scanner, and data acquisition are controlled by a computer. The system is not fixed to the vacuum chamber, and measurements could also be taken closer to the thruster. The maximum spacing from the thruster exit is approximately 8m. This paper presents the new system and shows measurements taken on out RIT thruster. Despite the low thruster power the signal is clear and not disturbed by noise. At the 3.85m distance from our RIT engine we can deduce a 90% power beam size with a radius of 0.6m, which corresponds to 8.8 degrees half angle.