An apparatus for measuring DT/K without in-vacuum mechanical motion

Abstract

A new drift-tube apparatus has been developed for measuring D T/K, the ratio of the transverse diffusion coefficient to the mobility of ions in a neutral gas under the influence of an electric field. It harnesses existing technology in mechanical, electronic, materials, and computer engineering. The main features are the ion current detector, which comprises 65 parallel rods, and an external mechanical multiplexer, which was designed to have extremely low (fA order) leakage currents and noise levels. Unlike with other earlier systems, the need for precise mechanical motion or adjustments of experimental conditions inside the drift tube during data collection has been circumvented. Its design therefore simplifies construction and makes operation less error prone. Data collection is computer controlled. A value for D T/K can now typically be obtained in less than 20 min, which greatly increases the rate at which results can be obtained as well as reduces the chance of unwanted variations in experimental conditions occurring during data collection. Results are estimated to be accurate to within 3%.