Robustness of ZAO based NEG pump solutions for fusion applications

Non Evaporable Getter (NEG) technology has been studied as an alternative pumping solution in facilities for fusion research since the 80 s. The recent development of a new generation of Zr-V-Ti-Al (ZAO®) getter alloys with improved features makes NEG technology an attractive option in several fusion applications, including in particular, Neutral Beam Injectors (NBI). The main advantages of ZAO® NEG pumps are related to the high pumping speed for H2, the high capacity that results into a very promising availability, the ease of integration and the low power consumption. From the vacuum point of view, research fusion facilities are in the high vacuum pressure range (e.g. 1∙10−6 ÷1∙10-5 Pa background pressure) and may present leaks and significant outgassing from internal components. Specific activities have been devoted to test the NEG pump robustness, i.e. the ability to maintain adequate performances in conditions very far from UHV. In particular, the effects of carbon oxides and hydrocarbon adsorption have been investigated, as well as the outgassing from materials like polyimide or even fluorinated polymers as PTFE. The results show that the ZAO® getter material is intrinsically robust, able to perform repeated H2 adsorption/desorption cycles with stable performances, and recover most of the original pumping speed even after significant exposure to hydrocarbons and fluorine species. These outcomes give promising indications for the future use of NEG solutions in real fusion facilities.