The CHEOPS VHP BB project consortium partner IOM was responsible for the task to design diagnostic tools for the plume characterization of very-high-power Hall effect thrusters (HET) with a power of up to 20 kW and to perform two test campaigns, one with the dual channel thruster TANDEM from Pisa University and Aerospazio, and one with der PPS-20k thruster from Safran Group.
Since many years, IOM has developed an advanced electric propulsion diagnostic (AEPD) platform in close collaboration with project partners, one of them being Aerospazio Tecnologie. The platform is of modular design. It uses several heavy-duty profiles, linear and rotary tables, such that it can be easily adapted to almost any test environment. A large number of diagnostic tools allow a comprehensive characterization of electric propulsion thrusters. Diagnostic tools include ion beam and plasma characterization tools, optical tools for inspection and wear characterization, and tools for characterization of the thruster surface temperature. The AEPD platform has been successfully employed on many gridded ion thrusters and Hall effect thrusters. Typical thruster power was 2 kW or less.
The new class of very-high-power Hall effect thrusters with beam powers of up to 20 kW bears some severe challenges or risks for the diagnostic tools. The higher power and higher beam current lead to significant heating and an increased wear of the materials exposed to the ion beam. Even a destruction of mechanical parts or electronic devices may occur.
Therefore, diagnostic tools must be critically reviewed. First steps included modelling the impact of the energetic particle beam onto the devices exposed to the beam in dependence on beam power and current, and time. The modelling showed that measurements inside the beam are feasible, but the setup must be completely re-designed and test procedures adapted for this purpose.
It was decided to use a Faraday boom for complete mapping of the current density distribution and a retarding potential analyser (RPA) for measuring ion energy distribution functions. The Faraday boom has a radius of 1 m and is equipped with 37 individual Faraday probes in total. 15 probes can be operated in parallel. The front and both sides of the Faraday boom are covered with graphite plates for shielding from the energetic particle beam. The RPA has a small front area for minimizing the interaction with the energetic particle beam. In total, the grids of the RPA have 147 holes and the collector 147 small cups. For the test campaigns, the IOM diagnostic system was installed in the large vacuum test facility LVTF-3 at Aerospazio. Operation tests of positioning system, Faraday boom and RPA were performed successfully [1,2].
With this, the diagnostic system was ready for the test campaigns with the two very-high-power Hall effect thrusters, the TANDEM thruster and the PPS®20k thruster.
The thrusters were operated with several operation parameter sets. Main thruster operation parameters were process gas, beam power, beam voltage, and beam current. IOM diagnostic tools performed very well for all operation points in both test campaigns [2]. Valuable information was gathered, which can help to evaluate the thruster performance and future optimization.
Current density mapping with the Faraday boom allowed assessing the stability of the thruster performance in dependence on operation parameters [2]. The current density is rotational symmetric for all operation points, but the amplitude of plasma oscillations varied strongly. Ion energy distribution measurements with the RPA revealed that the ion beam is not mono-energetic but rather bi-energetic. Experimental RPA data were also in part affected by secondary effects, which are tentatively assigned to the impact of energetic electrons.
Inspection of the diagnostic tools after completion of each test campaign showed no mechanical or electrical harm. However, the design of the RPA needs to be re-evaluated for future activities in order to avoid said secondary effects.
Both papers presented at the 39th International Electric Propulsion Conference Imperial College London, London, United Kingdom, 14-19 September 2025
[1] A. Piragon et al.,
Technology Demonstration testing of the PPS-20k Thruster,
IEPC-2025-647.
[2] S. Scaranzin et al.,
Characterisation of a 20 kW Dual Channel HT with Different Propellants (Xe/Kr/Ar),
IEPC-2025-735.
Leibniz-Institute of Surface Engineering (IOM), 04318 Leipzig, Germany
Dr. Carsten Bundesmann, Frank Scholze, Dr. Daniel Spemann (head)
