A vacuum pumping system comprises a first gas supply for supplying a first
gas, such as xenon, to a vacuum chamber. A pump receives the gas output
from the chamber. A second gas supply supplies a purge gas, such as
nitrogen or helium, for pumping with the first gas. A gas separator
receives the pumped gases exhausted by the pump, and recovers the first
gas and the purge gas from the stream. The recovered first gas is
recirculated through the vacuum chamber, and the recovered second gas is
recirculated through at least the pump.