| AVS 58th Annual International Symposium and Exhibition | |
| Vacuum Technology Division | Tuesday Sessions |
| Session VT+MN+NS+SS+AS-TuA |
| Session: | Surface Science for Future Electronic Materials and Accelerator Applications |
| Presenter: | Paolo Chiggiato, CERN, Switzerland |
| Authors: | V. Baglin, CERN, Switzerland G. Bregliozzi, CERN, Switzerland P. Chiggiato, CERN, Switzerland P. Costa Pinto, CERN, Switzerland J.M. Jimenez, CERN, Switzerland G. Lanza, CERN, Switzerland M. Taborelli, CERN, Switzerland C. Yin Vallgren, CERN, Switzerland |
| Correspondent: | Click to Email |
One of the main issues for the vacuum system of the Large Hadron Collider (LHC) is the build-up of electron clouds generated by electron multipacting in presence of beams. The occurrence of spatially distributed negative charges can lead to beam instabilities and emittance blow-up, pressure rises with a consequent background growth in the experimental areas, and increased thermal load in the cryogenic sections. The development of electron clouds depends on beam intensity and structure, magnetic field, and, in particular, the secondary electron emission of the beam pipe walls. With respect to this latter point, electron clouds can be eradicated whenever the maximum secondary electron yield becomes lower than a critical threshold. In the LHC the problem has already been tackled at the design phase by introducing TiZrV non-evaporable getter thin film coatings as the baseline for most of the room temperature sectors of the ring. After activation by in situ heating, this material provides maximum secondary electron yield lower than 1.1. In addition, during operation, dedicated scrubbing runs are carried out by generating intentionally electron clouds and electron impingement onto the non-coated vacuum chambers, in a way to reduce their secondary electron yield. Recently magnetron sputtered carbon coatings have been also studied because they can reach exceptionally low secondary electron emission without any heating; their application in the LHC injectors and future LHC components is under investigation.
The effect of electron clouds in the pressure variations during the first months of LHC operation will be presented, together with the effects ascribed to the mitigation techniques.