Abstract
1. Introduction
A Ti-Zr-V non-evaporable getter (NEG) coating, which was developed at CERN, is a breakthrough vacuum technology because it makes the vacuum chamber wall a getter surface by a low activation temperature around 180-300 degree C [1, 2]. The chamber itself can function as a vacuum pump by applying a NEG coating to the inner wall of the chamber. However, sticking probability for limited gas species, mainly such as H2 and CO, has been reported in the previous research. In this research the pumping speed measurement for the H2, CO, O2, CO2, and N2 was performed by the orifice method using the NEG-coated chamber of 100 mm diameter and 200 mm length. Furthermore, the pumping speed deterioration by repetitive air exposure and re-activation was evaluated for such gas species.
2. Experiment
The pumping speed was measured by repeating 15 times in one set "After opening to atmosphere → Vacuum evacuation → Baking (Activation) with 20 degree C for 8.5 hours → pumping speed measurement". Figure 1 shows the configuration of the measurement setup. P1 chamber (NEG coated) and P2 chamber were connected by an orifice of 1.75x10-2m3/s(N2), and gas was induced from the P1 side. Figure 2 shows the measurement results for various gases. It was found that while the pumping speed for H2, CO, CO2, N2 other gases was degrading, O2 was degrading slowly and was still above 1000 L/s at the 15 times cycle. In the conference, we report the details of the experiment and the measurement results.
Fig. 1 Schematic diagram of the apparatus used to measure pumping speed. TMP: turbomolecular pump; DSP: dry scroll pump; EXG: extractor gauge, RGA: residual gas analyzer; and CDG: capacitance diaphragm gauge.
Fig.2 Pumping speed measurement results for various gases
References
[1] C. Benvenuti, et al., VACUUM 50, 57 (2001).
[2] O. B. Malyshev, et al., Journal of Vacuum Science & Technology A 27, 321 (2009).
