Combination of compact nonevaporable getter and small ion pumps for ultrahigh vacuum systems

Abstract

The rapid pumpdown of ultrahigh vacuum (UHV) systems, achieved with a very short and low temperature baking or even without baking, is appealing in a variety of research and industrial applications. The use of small volume, compact pumps delivering very high pumping speed is also attractive since it allows minimizing the overall size and weight of the vacuum system, simplifying its design. In the present article, the authors report the results of the pumping experiments carried out on a vacuum chamber pumped by a compact nonevaporable getter (NEG) pump (Capacitorr D 400-2® model, SAES Getters SpA, Italy) and by a small sputter ion pump (SIP). To measure the effective contribution of the NEG to the overall pumping, vacuum tests were carried out in a wide range of situations, with/without NEG pump, with/without baking, and changing the pumping speed of the SIP from 60 to 10 l/s (N2). Significantly lower pressures and faster pumping could be achieved using the NEG pump. Base pressures of low 10−11 mbar could be obtained in the authors’ experimental system with the compact NEG assisted by the 10 l/s SIPs after a 48 h bake-out. The results also show that the system with NEG reached 10−11 mbar after a very short (few hours) bake-out. The base pressure was 1×10−10 mbar with 60 l/s SIP alone after a 48 h bake-out, whereas it was 7.9×10−11 mbar when combined with the NEG, a better result after only 2 h bake-out. This is quite a remarkable decrease in the bake-out time of a UHV system. It is worthwhile to note that UHV could also be achieved with the NEG even in a fully unbaked system. The pressure of 8×10−9 mbar reached with the SIP alone dropped to 3.9×10−10 mbar after adding the NEG. The other interesting result of the NEG-based system is that the pressure increase is much slower when the SIP is switched off. This is also a good characteristic, required for portable vacuum devices, such as UHV suitcases and more generally for systems hosting sensitive materials or components, which can be affected by the pressure increase following a power interruption.