The STAR TPC has been operating with P10 (90% Ar, 10% methane by volume) at ~2 mbar above the ambient atmospheric pressure. Temperature is regulated close to 75F, both for the hall [supposedly regulated at (75 +/-5)F] and for the TPC itself via water cooling. Typically, the electric field in the drift volume is close to 148 V/cm. This is somewhat above the saturation value (~135 V/cm), so that the drift velocity can be regulated by varying the field.
In addition to P10 literature values, some internal information exists in STAR:
It is anticipated that, in the future, He-Ethane 50-50 might be used, instead of P10. This would also be near ambient pressure and temperature, but at a higher electric drift field.
A small amount of internal He-ethane data also exists: