Optimization of a Faraday Cup Collimator for Electric Propulsion Device Beam Study: Case of a Hall Thruster.

Featured Application: Over the last decade electric propulsion devices have evolved from laboratory units to qualified space hardware. Due to the diversity of concepts numerous electric thruster technologies are available on the new space market. Each technology has a specific working principle which implies a wide variety of plasma discharges and ion beams. Currently, it is still difficult to compare, without bias, these plasmas to each other with standard devices and procedures. This work aims at contributing to the effort towards standardization of a specific type of plasma diagnostic called a Faraday cup. This instrument is of great importance as it measures the ion current density in electric thruster plumes. This physical quantity provides information on key parameter for thruster development and production such as thrust, beam divergence, ionization degree and propellant use. In this contribution we describe and validate the optimization of a Faraday cup collimator in the case of Hall thrusters. A Faraday cup (FC) is an instrument dedicated to current measurement in beams, jets and plasmas. It consists of a set of polarized electrodes mounted in such a way plasma sheath effect can be neglected, yielding accurate and reliable results. A FC is composed of three main parts, namely a collector or cup, which collects the current, a collimator, which defines the collection area and can contribute to limit electrons from entering the cup and a housing which protects the instrument from perturbation caused by the surrounding medium. In this paper, we provide experimental results of the effect of the collimator upon the measured ion current within the beam of a low-power Hall thruster. Different collimator materials, aperture diameters and polarization voltages are studied to determine the optimum design. Minimum dimension as well as appropriate materials are given as a conclusion in the case of low-power Hall thruster beam investigation. [ABSTRACT FROM AUTHOR]