Beyond Ti-Zr-V: present development on thin-film coatings for beam pipes

Since 1997, Ti-Zr-V thin films have been studied to provide a solution to the problems of both pressure distribution and electron cloud build-up in beam pipes. Nowadays, this material is coated on the whole inner surface of vacuum chambers providing large pumping speed, low degassing rate and secondary electron yield. These favourable characteristics are obtained after heating in vacuum at temperatures higher than 180 °C. Unfortunately, heating at such temperatures is not always possible for the future CERN projects: in some cases, magnet designs impose lower heating temperatures; in other cases, heating is not allowed at all, as for most of the existing SPS vacuum chambers. To overcome these limitations, two lines of development have been drawn; if pursed successfully, they will allow the production of both NEG films with lower activation temperature (150 °C being our target) and films or surface treatments providing low secondary electron yield without any heating.