Erlangen 2026 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 21: Codes and Modeling II

P 21.1: Hauptvortrag

Freitag, 20. März 2026, 09:00–09:30, KH 01.013

Performance Pitfalls and Design Principles of Retarding Potential Analyzers — •Thomas Trottenberg — Institute of Experimental and Applied Physics, Kiel University, Kiel, Germany

Retarding potential analyzers (RPAs) are standard diagnostics for ion energy distribution measurements, yet their performance is often limited by subtle but critical mechanical design choices. Grid alignment, aperture geometry, grid thickness, and spacing can strongly affect the measured current-voltage characteristics and may introduce non-monotonic behavior and artificial humps.

In this talk, experimental results and trajectory simulations of a four-grid RPA with drilled grids are presented, systematically quantifying the impact of grid orientation and hole geometry. It is shown that certain grid alignments introduce strong correlation effects between adjacent grids, resulting in enhanced transparency and pronounced anomalies close to the falling edge in the characteristics.

These findings reveal fundamental performance pitfalls of RPAs and form the basis for practical design guidelines. Concrete recommendations for grid geometry and alignment are derived, aiming at robust, monotonic characteristics and reliable ion energy distribution functions.

Keywords: Retarding potential analyzer; Ion energy distribution; Ion beam diagnostics; Electric propulsion