Instrument for spatially resolved simultaneous measurements of forces and currents in particle beams

Abstract

The article presents a device for spatially resolved and simultaneous measurements of forces and currents in particle beams, especially in beams composed of ions and neutral atoms. The forces are exerted by the impinging beam particles on a plane circular conductive target plate of 20 mm diameter mounted on a pendulum with electromagnetic force compensation. The force measurement in the micronewton range is achieved by electromagnetic compensation by means of static Helmholtz coils and permanent magnets attached to the pendulum. Exemplary measurements are performed in the 1.2 keV beam of a broad beam ion source. The simultaneous measurements of forces and currents onto the same target are compared with each other and with Faraday cup measurements.

Force probes for development and testing of different electric propulsion systems

“…2 Laboratory for Enabling Technologies, Airbus, Friedrichshafen, Germany. 3 Institut de Combustion Aérothermique Réactivité et Environnement, Orléans, France. 4 Institute of Aerospace Engineering, Chair of Space Systems, Technische Universität Dresden, Dresden, Germany.…”

“…In case of measurements in the plume of electric thrusters, commonly electrostatic probes, like Faraday cups and retarding potential analyzers, are used [1]. The measurements of flux densities with Faraday cups are affected by charge-exchange collisions because neutral beam particles created by charge-exchange collisions cannot be detected [2,3]. The thrust of an electric engine is commonly measured by thrust balances [4].…”

“…These measurements account for neutral particles but they are not plume diagnostics. The force probe enables to perform spatially resolved plume measurements that do not discriminate between ionic and neutral plume particles [3,5]. Therefore, one could say that force probes combine the non-discriminating aspect of thrust balances with the spatial resolution of Faraday cups.…”

An interferometric force probe for beam diagnostics and the study of sputtering

“…In comparison with our formerly reported force measurements that used electromagnetically compensated pendula [6,11,16,17], the here presented probe is based on a sensitive cantilever whose deflection is measured interferometrically along two axes.…”

“…Spectroscopic techniques like optical emission spectroscopy [3], laser absorption spectroscopy [4], and laser-induced fluorescence [5] are also applied, but less frequently. Recently, force measurements were performed in the beam of an industrial broad-beam ion source that is very similar to the plume of gridded ion thrusters [6]. The advantage of the force measuring method over the standard electric techniques is that the latter are sensitive only for the charged species.…”