Sey and Electron Cloud Build-up with Neg Materials

A. Rossi, CERN, Geneva, Switzerland Abstract The LHC room temperature sections will be coated with non-evaporable getter (NEG) materials for, among other reasons, their properties of antimultipactor. Laboratory measurements of secondary electron yields (SEY) of TiZrV NEG coatings have shown that after 2 h heat treatment at 160 and 200 C, the maximum SEY decreases from 2 to below 1.4 and 1.1 respectively. Saturation with H2, H2O, CO and CO2 at low pressure increases the SEY by about 0.1. This outcome is supported by the results on a NEG-coated chamber in the SPS accelerator ring, with LHC type proton beam. The untreated NEG surface multipacts as any unbaked surface, while no electron cloud build-up was observed after 4 h heat treatment at 250 C and subsequent saturation, mainly with water vapour. We give here a summary of secondary electron yield (SEY) measurements on NEG surfaces and present the results of electron cloud build-up measurements with NEG-coated vacuum chambers.