Planar probe array for bidimensional mapping of the ion flux profile of a miniaturized ion thruster

The characterization of the plume profile of low-power ion thrusters is imperative for the evaluation of the impacts in performance caused by the miniaturization process. Here we present the development of an instrument, consisting of an automatized array of planar probes, capable of performing two-dimensional mappings of the ion current density profile produced by the thrusters. In order to validate the instrument, we conducted experiments using a low power gridded ion thruster NPT-30. The collected data and proposed procedure to extract both information about total ion current and divergence half-angle of the two-dimensional maps are also presented. The results of the experiments show a close agreement between the ion current measured and the expected values for the operational regimes of the thruster. It is also shown that the divergence halfangle has a decreasing profile with perveance within the range studied here, showing that the thruster is operating under sub-optimal regime over the chosen operational points. Nomenclature A0 = area of central probe, m 2 Te = electron temperature, eV Aeff = effective probe area, m 2 Vp = probe bias voltage, V Ai = estimated probe area, m 2 α = divergence half-angle, rad a, b = parameters of Sheridan's model η = parameter of Sheridan's model D = diameter of the probe, m λ = great-circle central angle, rad Ib = total ion current, A λD = Debye length, m 2 Ib,a = axial ion current, A ρp = parameter of Sheridan's model Ji = ion current density, A/m 2 φ0 = position of central probe, rad Np = total number of probes φi = estimated probe position, rad R = radius of the instrument arc, m φf = position of final probe, rad