In a system for processing gas, a gas analyzer in a gas analyzer chamber measures a quantity of ions generated from a gas. An ionization source includes an ionization chamber and an electron source for generating ions for the gas analyzer. The ionization chamber encompasses an ionization region in which particles of the gas are charged to form the ions. A channel directs the gas from a gas source into the ionization chamber, and the channel extends to a surface of the ionization chamber. An ionization source vacuum pump is in gaseous communication with the ionization chamber via a substantially large opening, and operates to draw gas from the ionization chamber.