Measurement of electron mobility in liquid and gaseous Ar at low electric field strength and in the critical region

The mobility of excess electrons in argon has been determined from drift-time measurements using the pulse-shape method. The electrons were generated by pulsed emission from a photocathode. Results of measurements at low electric field strengths (E>1 V/cm) and in the thermodynamic critical region with a temperature resolution of 0.2 mK are reported. At the mobility maximum, observed at ~(T _c-5) K, an increase of the mobility, down to the lowest field strengths measured, is found. The critical mobility at low field strengths is determined to be μ_c≈160 cm² V ^-1 s^-1