The violet light is produced by the argon plasma used when sputtering the amorphous carbon. The the beam screen is coated using the magnetic field of the quadrupole itself. ((mage : Pedro Costa Pinto).
The electron cloud problem needs to be addressed with innovative solutions, particularly in view of the rapidly approaching HL-LHC upgrade. CERN’s Vacuum, Surfaces and Coatings group has greatly improved its amorphous carbon coating technique, which is an alternative to the scrubbing process used so far. This technique is now fully mature and is being used for the vacuum chambers of the SPS magnets and the delicate beam screens of the LHC’s quadrupole triplets. Read more in the Bulletin.