Influence of Cathode Boundary and Initial Electron Swarm Width on Electron Swarm Parameter Determination with the Pulsed Townsend Experiment

Abstract

The Pulsed Townsend experiment enables the extraction of relevant electron transport properties in different gases such as the electron drift velocity $W$ (or equivalently the mobility $\mu$), the longitudinal diffusion coefficient $D_{\mathrm{L}}$, and the effective ionization rate $R_{\mathrm{net}}$ (or equivalently the effective ionization coefficient $\alpha_{\mathrm{eff}}$). Existing analysis techniques lack an accurate representation of the experimental initial and boundary conditions. This work provides an improved evaluation approach by appropriately considering both initial and boundary conditions in order to extract more accurate swarm parameters from measurement data. Simulative and experimental measurement results verify an increased evaluation accuracy. Furthermore, the longitudinal diffusion coefficient $D_{\mathrm{L}}$ can now be accurately extracted from Pulsed Townsend measurements, which was previously not possible with existing evaluation approaches. The developed curve fitting code is made publicly available.