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We present a combined electrostatic and magnetostatic plasma diagnostic tool used to measure current fractions of ion species in a Hall-effect thruster plume. Hall thrusters produce thrust by accelerating singly and multiply charged ions to high velocity. Singly charged ions fall through potential differences from their point of creation to the location of measurement, which varies as a function of time and position resulting in a relatively wide distribution of energy. This process is further complicated by both direct and multi-step creation of multiply charged ions and by ion-neutral collisions. The result is that Wien velocity filter (ExB) spectra typically have overlapping peaks. Analysis of these spectra requires assumptions about the velocity distribution function (VDF) that are hard to verify and can result in the incorrect species current distribution used to calculate thruster performance efficiencies. We present how adding an energy filter in line with an ExB probe can result in a more accurate measurement of the species current fraction while also providing information about the ion energy distribution of each species. The combined diagnostic was used to measure the species current distribution in a 1.5 kW Hall thruster operating on krypton. The diagnostic setup and data analysis of the probe measurements are presented and compared against results utilizing established VDF-fit and integration techniques applied to standard spectra measured by a standalone ExB probe. [ABSTRACT FROM AUTHOR]

We designed and built a compact bi-axial electron beam separator. This separator is an indispensable electron optical element in the development of MEMS-mirror-based miniaturized concepts for quantum electron microscopy (QEM) and aberration-corrected low-voltage scanning electron microscopy (AC-SEM). The separator provides the essential cycling of the electron beam between the two parallel optical axes that are part of these systems. This requires crossed electric and magnetic fields perpendicular to the beam path, as can be found in Wien-filter type beam separators. In our miniaturized QEM or AC-SEM concepts, the parallel axes are separated by only 1 mm. Conventional Wien-filter-based beam separator concepts rely on in-plane electric and magnetic multipole electrode configurations that are larger than the restricted available volume in these miniaturized QEM/AC-SEM systems. Our compact beam separator design introduces three stacked dipole electrode layers, which enables simultaneous beam separation at two parallel axes that are in close proximity. The outer layer electrodes maintain an electric field for which the direction on the one axis is opposed to that on the other axis. The middle layer generates a perpendicularly oriented magnetic field that spans both axes. The total field configuration enables the deflection of the beam on one axis and simultaneously provides a straight passage on the other axis. The deflection strength and distortion fields of the beam separator are experimentally obtained with a 2 keV electron beam energy. The results validate the use of the beam separator for electron energies up to 5 keV and deflection angles up to 100 mrad. [ABSTRACT FROM AUTHOR]