Detailed precision and accuracy analysis of swarm parameters from a pulsed Townsend experiment

Abstract

A newly built Pulsed Townsend experimental setup which allows to measure both electron and ion currents is presented. The principle of Pulsed Townsend measurements itself is well established to obtain swarm parameters such as the effective ionization rate coefficient, the density-reduced mobility and the density-normalized longitudinal diffusion coefficient. Main novelty of the present contribution is a detailed and comprehensive analysis of the entire measurement and evaluation chain with respect to accuracy, precision and reproducibility. The influence of the input parameters (gap distance, applied voltage, measured pressure and temperature) is analyzed in detail. An overall accuracy of $\pm$0.5\% in the density reduced electric field ($E/N$) is achieved, which is close to the theoretically possible limit using the chosen components. The precision of the experimental results is higher than the accuracy. Through an extensive measurement campaign, the repeatability of our measurements proved to be high and similar to the precision. The reproducibility of results at identical ($E/N$) is similar to the precision for different distances but decreases for varying pressures. For benchmark purposes, measurements for Ar, $\mathrm{CO_2}$ and $\mathrm{N_2}$ are presented and compared with our previous experimental setup, simulations and other experimental references.