Numerical simulation of experimental tests performed on ZAO® Non- EvaporableGetter pump designed for NBI applications

Vacuum systems of neutral beam injectors have very demanding requirements in terms of pumping speed, throughput and capacity. Due to its high affinity to hydrogenic species, porous sintered non-evaporable getters (NEG) are a possible candidate for the deployment in giant hydrogen ion sources and neutral beam injectors for fusion. This paper presents the numerical interpretation of experimental tests on a recently developed NEG cartridge, part of a modular pump under development for neutral beam injectors. The cartridge is composed by six stacks of ZAO® porous sintered NEG disks and a heater. It was tested under hydrogen loads relevant for neutral beam injectors, namely at constant pressure or constant flow, such that the hydrogen pressure was in the range 20 mPa / 40 mPa. The result of the sorption test was reproduced by a three dimensional flow simulation in molecular regime, to determine the actual pumping speed, the effective sticking coefficient, and the uniformity of the gas load on the various NEG disks. The regeneration procedure was analyzed to determine the desorption rate per unit area and to compare with the equilibrium isotherms. The procedure developed, and the results obtained, provide the basic understanding for interpreting the large-scale tests on the modular pump, consisting of 34 of these cartridges.