Dr. Valentine Petit

CERN, Switzerland
After an Engineer’s degree in Material Science in Grenoble, France, Valentine joined the Vacuum, Surfaces and Coatings group at CERN for her PhD in 2016. Since then, she specialized in surface science with a focus on particle accelerator applications. In particular, she studied the effect of electron irradiation of surfaces at ambient and cryogenic conditions, to explain beam pipe conditioning related to electron multipacting in particle accelerators. In addition, she also explores, develops, and characterizes anti-multipacting surface treatments which could be deployed in-situ, in the kilometers-long beam pipe of the Large Hadron Collider.

Talk title: Surface technology for electron multipacting mitigation in the Large Hadron Collider vacuum system: developments towards in-situ implementation
Electron clouds arise in modern particle accelerators with high intensity and positively charged beams due to the exponential multiplication of electrons in the vacuum beam pipe. In the Large Hadron Collider (LHC) at CERN, electron clouds are observed through beam quality degradation, pressure rises and heat loads in the cryogenic sections hosting the superconducting magnets. In particular, electron clouds have been identified as critical limitation to the beam intensity achievable by the High-Luminosity upgrade of the LHC (HL-LHC).

To tackle this performance-limiting phenomenon, several mitigation techniques have been developed in the last decades, including clearing electrodes, confinement of electrons by solenoids or lowering the Secondary Electron Yield (SEY) of the beam pipe surface, the quantity governing the multiplication of electrons, either by a low-SEY thin film coating or by roughening the surface via a laser treatment. For the LHC, an additional constraint is the necessity to deploy such a mitigation technique in-situ, over several tens of meters of beam pipes already embedded in cryogenic magnets and installed in the underground tunnel. This talk will present the developments related to the preparation of the in-situ deployment of two processes for electron cloud mitigation, namely amorphous carbon coatings and laser-induced surface structuring. The optimization of the treatment conditions to obtain the best performance will be addressed by considering the constraints when upscaling the technology to vacuum pipes of long length within the geometrical configuration of the LHC cryo-magnets.