• plume
• hollow cathode
• diagnostic
• triple langmuir probe

Hollow cathodes are sources of electrons used for gas ionization and beam neutralization in Hall effect thrusters.
Most of the studies available in the literature are focused on the internal regions, since these are the ones that drive the performance of a hollow cathode.
Other works concentrate their efforts on the study of the plasma exiting from the cathode, namely the plume as a matter of fact, high-energy ions in the cathode plume are identified as the main cause of the keeper erosion that limits the life of the cathode. To characterize the plasma properties, the most common device is the Langmuir probe, which provides information about the plasma density, the electron temperature and the plasma potential.
This work was aimed at designing an experimental setup to perform Langmuir probe measurements in the plume of a 60 A-class hollow cathode.
The applicability of the triple Langmuir probe for the diagnostics of the cathode plume was first assessed. An experimental campaign was then set up by using three probes, controlled by a dedicated positioning system. Preliminary results will be presented, in terms of plasma density and electron temperature obtained with the collected data.
Next activities will include further measurements of the plasma plume properties for different cathode operating conditions, as well as comparisons between the experimental data and theoretical results coming from a previously developed model.