【加速器セミナー II】NEG coating developments and optimization at ASTeC

概要

The ASTeC Vacuum Science Group has an ongoing study on improving the non-evaporable getter (NEG) coating which is currently used in many accelerators around the world.
The main advantages of using NEG coatings are, evenly distributed pumping speed, low thermal outgassing rates and low photon and electron stimulated gas desorption (PSD and ESD).
Our recent work demonstrated that NEG coating can be optimized for various applications for having higher pumping speed, lower activation temperature or/and lower PSD/ESD.
It was shown that NEG act as an effective barrier for hydrogen diffusion from the bulk of vacuum chamber and this is the most important function of it.
The properties could be further improved by vacuum firing of the vacuum chamber before the NEG deposition, choosing the NEG composition and deposition parameters.
NEG coatings may affect the beam impedance in high frequency machines such as FEL.
The bulk conductivity of two types of NEG films (dense and columnar) was determined by measuring the surface resistance of NEG-coated samples using an RF test cavity and fitting the experimental data to a standard theoretical model.
The conductivity values obtained are then used to compare resistive wall wake field effects in beam pipes coated with either of the two types of film.
The bulk conductivities are σd=1.4×104 S/m for the columnar NEG coating and σd=8×105 S/m for the dense NEG coating.