Ion analytical characterisation of the RIT 22 ion thruster

We present the energy-selective mass spectroscopy (ESMS) as a very useful tool for the characterisation of the discharge chamber plasma and the ion beam. The beam composition, particularly the content of multiply charged ions and contaminations can be studied. From the energy distributions, information on the plasma properties and processes occurring in the plasma and the beam can be obtained. Modification of the spectrometer to allow the analysis at higher ion energies (up to 5 keV) is described. First results of the characterisation of the RIT-22 ion thruster are presented. The basics of radio-frequency ionisation are well understood. Nevertheless, more detailed knowledge of the discharge processes would allow for further performance improvements. Therefore, fast non-intrusive diagnostic methods are from growing interest. Optical methods like LIF and OES were successfully established for plasma monitoring of ion engines and plasma thrusters. In contrast to Langmuir probe measurements, optical diagnostics give access to neutral particles also. Although these methods offer many advantages their implementation is challenging. In respect to measurements on flight-hardware the above methods have one decisive disadvantage: hardware modifications (e.g. optical viewports or windows) are required. Here, we present an interesting non-intrusive approach to the plasma properties - the energy selective mass spectrometry (ESMS) or, as it is sometimes called plasmamonitor. Observing the ionic species, their densities and energy distributions in the beam gives meaningful insights into the discharge chamber. For that the ion thruster to be examined remains as is. Besides the access to discharge parameters this beam diagnostic delivers detailed information of the ion beam too. The angular distribution of ion emission and their energy can be investigated not only from beam ions, but also from secondary ions. The divergence angle can be deduced. These results are from crucial interest with respect to thruster-spacecraft interaction, e.g. the impact of energetic ions on solar cells.