# Electron Drift and Longitudinal Diffusion in High Pressure Xenon-Helium Gas Mixtures

## TL;DR

This study measures electron drift velocity and diffusion in xenon and xenon-helium mixtures at various pressures and electric fields, revealing larger than expected diffusion at low fields but confirming helium's potential to reduce transverse diffusion.

## Contribution

The paper provides new experimental data on electron transport in xenon and xenon-helium mixtures, highlighting discrepancies with theoretical predictions at low fields and supporting helium's use to improve detector performance.

## Key findings

- Longitudinal diffusion exceeds theoretical predictions at low E/P in pure xenon.
- Drift velocities in xenon-helium mixtures match theoretical models.
- Helium additives may effectively reduce transverse diffusion in xenon detectors.

## Abstract

We report new measurements of the drift velocity and longitudinal diffusion coefficients of electrons in pure xenon gas and in xenon-helium gas mixtures at 1-9 bar and electric field strengths of 50-300 V/cm. In pure xenon we find excellent agreement with world data at all $E/P$, for both drift velocity and diffusion coefficients. However, a larger value of the longitudinal diffusion coefficient than theoretical predictions is found at low $E/P$ in pure xenon, below the range of reduced fields usually probed by TPC experiments. A similar effect is observed in xenon-helium gas mixtures at somewhat larger $E/P$. Drift velocities in xenon-helium mixtures are found to be theoretically well predicted. Although longitudinal diffusion in xenon-helium mixtures is found to be larger than anticipated, extrapolation based on the measured longitudinal diffusion coefficients suggest that the use of helium additives to reduce transverse diffusion in xenon gas remains a promising prospect.