Electron cloud is presently a limitation for the performance of many existing machines (e.g. the SPS), as well as a serious feasibility issue for future circular facilities, designed to operate with high currents within small apertures (like the CLIC damping rings). That's why several techniques of electron cloud mitigation or suppression are presently under study. One of the most promising solutions to date is the use of amorphous C coating layers on the inner wall of the beam chambers. This coating can significantly lower the Secondary Electron Yield (SEY) of the surface. Tests with protons in the SPS have confirmed this property and, furthermore, have shown that it does not deteriorate with aging and exposition to air.
Tests with positrons/electrons are currently being made in Cesr-TA (Cornell University). A Cesr-TA vacuum chamber was sent to CERN last spring, where it was coated and later shipped back to Cornell for installation into the ring. The C-coated chamber has been placed downstream from a bending section, where it is hit by synchrotron radiation. A reference Al-chamber in a specular position is monitored for direct comparison. The diagnostics on both the C-coated and the reference chamber includes electron cloud strip monitors, RFAs, RGAs and pressure gauges. The results of some measurements taken during the July 2009 Cesr-TA run will be the main focus of this seminar.