Aging effect of non-evaporable getter coatings
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ORIGINAL PAPER
Aging effect of non‑evaporable getter coatings Yuchen Yang1 · Yongsheng Ma1,2 · Shuangkai Chen1 · Tiezhu Qi1 · Xiaohua Peng1 · Haiyi Dong1 · Ping He1 Received: 25 May 2020 / Revised: 7 July 2020 / Accepted: 13 July 2020 © Institute of High Energy Physics, Chinese Academy of Sciences 2020
Abstract Introduction The pumping performance of getter materials has becoming one of the hotspots in accelerator field. The recovery of pumping performance after air venting, also called aging effect, is important for applications in accelerators. Materials and methods In this work, we investigated the aging effect of Ti–V–Zr–Hf- and Ti–V–Zr-coated copper tubular chambers, and the effect of initial air exposure time on the aging properties. The samples presented hierarchically micro/ nano-structures and showed a featured aging curve, giving about 9 effective pumping cycles. Conclusion The pumping performance is inversely correlated with air exposure time suggesting that the getter coated chambers should be properly preserved before applied as a “pump”. Keywords Aging · Non-evaporable getter · Pumping speed · Air exposure
Introduction
Experiment
CERN [1] originally invented getter coating for accelerator vacuum chamber and it is now widely used in many accelerator centers. A getter material can chemically react with the residual gas species in vacuum, working like a “pump” to provide higher vacuum. Typical gases present in vacuum systems are carbon monoxide (CO), carbon dioxide (CO2), nitrogen (N2), hydrogen ( H2) and water vapor ( H2O). After “pumping”, a protective compound layer forms on the getter surfaces, which under vacuum and at high temperature can dissolve and diffuse into the bulk before it can be effectively “pumping” again. The pumping speed, sticking probability and pumping capacity of getters have been widely studied for many years [2, 3]. However, in practical applications the pumping properties would decay after each pumping cycle (or air exposure), it is therefore important to study the aging effect [4, 5] (recovery after air venting) of getter coatings. In this context, we investigated the aging effect of Ti–V–Zr–Hf- and Ti–V–Zr-coated copper chambers, and the effect of initial air exposure time on the aging properties.
The aging effect has been studied with pumping properties measurement system. The system used for pumping speed and pumping capacity measurement of NEG-coated chambers is shown in Fig. 1. The NEG-coated copper chamber was installed on the measurement system. One end of the coated chamber was connected to the gas inlet and a sputter ion pump (SIP) of 100 l s−1 pumping speed, through the orifice. On both sides of the sample and the orifice, the chambers had Bayard Alpert gauges and residual gas analyzers (RGA) for total and partial pressure measurements. To check the pumping performance, CO and H2 gases were injected through a calibrated leak valve. After installing a sample on the measurement system, the chamber was pumped and baked to 250 °C for 48 h while the NEG-c
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