W. Tang

Measurement of Longitudinal Electron Diffusion in Liquid Argon

Abstract We report the measurement of longitudinal electron diffusion coefficients in liquid argon for electric fields between 100 and 2000xa0V/cm with a gold photocathode as a bright electron source. The measurement principle, apparatus, and data analysis are described. In the region between 100 and 350xa0V/cm, our results show a discrepancy with the previous measurement [1] . In the region between 350 and 2000xa0V/cm, our results represent the world׳s best measurement. Over the entire measured electric field range, our results are systematically higher than the calculation of Atrazhev‐Timoshkin [2] . The quantum efficiency of the gold photocathode, the drift velocity and longitudinal diffusion coefficients in gas argon are also presented.

Modeling electronegative impurity concentrations in liquid argon detectors

We present a simple mathematical model of the dynamics of impurity distribution in liquid argon detectors. This model considers the dominant sources, sinks, and transport of the impurity between and within the gas and liquid phases of a large detector. We use this model to extract Henrys coefficients for oxygen and water from the time dependence of the impurity concentration in the liquid phase, while the gas in the detector volume is being purified. We find that Henrys coefficient for oxygen in liquid argon is 0.9, in agreement with previous measurements by other methods. For water we obtain the first measured value of Henrys coefficient in liquid argon of ∼ 1.0. This value is in reasonable agreement with the value estimated from the ideal solution theory using an extrapolation of the water vapor pressure.

A 20-liter test stand with gas purification for liquid argon research

We describe the design of a 20-liter test stand constructed to study fundamental properties of liquid argon (LAr). This system utilizes a simple, cost-effective gas argon (GAr) purification to achieve high purity, which is necessary to study electron transport properties in LAr. An electron drift stack with up to 25 cm length is constructed to study electron drift, diffusion, and attachment at various electric fields. A gold photocathode and a pulsed laser are used as a bright electron source. The operational performance of this system is reported.