In the frame of the GIESEPP MP project the Aerospazio activity will also be aimed at the demonstration and validation of advanced diagnostics, including laser spectroscopy techniques for not intrusive plasma property measurements of the plume of the thrusters. GIESEPP MP consortium partner Aerospazio has a specific expertise on long term testing (several thousand hours of endurance/life testing) as well as accurate performance measurements (plume propagation and operational characterisation).
Several type of sensors for plume diagnostics are mounted on a semicircular boom (Fig. 1) rotating inside the vacuum chamber allowing measurements on a hemispheric surface of the thruster plume (Fig. 2)
The data gathered are used to calculate plume parameters at different angles from thruster centerline. For example, for Faraday probes, the measurements are interpolated to obtain a 3D and contour map of current densities and used to calculate:
- current density plot for each Faraday probe
- current density 3D plot
- current density contour plot
- the overall ion beam current exhausted from the thruster
- beam divergence
- beam axis deviation
The following Fig. 3 shows an example of current density data acquired on a reference thruster by the probe scanning on the horizontal plane [Ref. F. Scortecci, E. Bonelli, B. Michelozzi, F. Saito, S. Scaranzin, A. Turco, “PERFORMANCE OF A LARGE VACUUM FACILITY FOR SPACECRAFT PROPULSION TESTING”, Proceedings of the 4th International Spacecraft Propulsion Conference (ESA SP-555). 2-9 June, 2004, Chia Laguna (Cagliari), Sardinia, Italy]. It is possible to note that the data acquired during the forward boom scan (blue “x” points) are consistent with data from the subsequent backward scan (red “+” points).
For the same reference, the following Fig. 4 shows a 3D map of the ion current densities in the plume obtained by interpolating the probe data and the related levels contour map.
