Creation of extreme high vacuum with a turbomolecular pumping system: A baking approach

Pressures in the low 10^-12 Torr range are produced by a 200 °C bakeout with a turbomolecular pumping system. A small molecular drag pump in conjunction with the membrane pump turns out to be an effective means of achieving low backing pressures. The stainless-steel test chamber of 6800 cm² surface area has been prebaked to 450 °C. An ultimate pressure of 1X10^-12 Torr is obtained on the extractor gauge and to date this is the lowest pressure attained with turbomolecular pumps only. This system offers simplicity of arrangement, ease of operation, rather low cost, and fast pumpdown to ultrahigh vacuum. The pressure reaches 2X10^-9 and 4X10^-11 Torr at 2 and 83 h, respectively, after startup without bakeout when vented to atmospheric pressure using extremely dry nitrogen.