Influence of CuO thin film morphology on secondary electron emission: implications for the electron cloud phenomenon in high energy accelerators

Abstract During LHC Run 2, unexpected beam-induced heat loads on the pipe walls were observed in certain parts of the accelerator. This effect was attributed to the build-up of electron clouds, the intensity of which was unusually exacerbated by a high secondary electron yield (SEY) from the copper beam screen surface of the LHC. This abnormally high SEY value was linked to the presence of CuO oxide on the walls, rather than the native Cu 2 O oxide typically found on the surfaces. The presence of CuO is believed to inhibit the conditioning effect of the walls, which normally allows the SEY to naturally decrease as the accelerator operates. To investigate the effect of CuO on secondary electron emission from copper, we carried out laboratory studies on CuO thin films deposited using two different methods (chemical bath deposition and metal–organic chemical vapor deposition). After characterization, the SEY of the films was measured, and the electron emission properties were correlated with the structure and morphology of the studied layers. Surprisingly, the SEY of CuO deposited by CBD falls below 1 after electron conditioning. This result opens the way to a potential method for reducing the SEY of copper surfaces in accelerator beamlines.