A liquid nitrogen cooled cryoshroud is located between the chamber walls and the CAR and acts as an effective pump for many of the residual gasses in the chamber. This pumping arrangement can keep the partial pressure of undesired gasses, such as H₂O, CO₂, and CO to less than ~10^-11 Torr. The substrate holder and all other parts that are heated are made of materials such as Ta, Mo, and pyrolytic boron nitride (PBN) which do not decompose or outgas impurities even when heated to 1400ºC. To monitor the residual gasses, analyze the source beams, and check for leaks, a quadrupole mass spectrometer (QMS) is mounted in the vicinity of the CAR.