Detailed investigation of the low energy secondary electron yield of technical Cu and its relevance for the LHC

Abstract

The detailed study of the low energy secondary electron yield (LE-SEY) of technical Cu for low electron energies (from 0 to 20 eV) is very important for electron cloud build up in high intensity accelerators and in many other fields of research. Different devices base their functionalities on the number of electrons produced by a surface when hit by other electrons, namely its SEY, and, in most cases, on its very low energy behavior. However, LE-SEY has been rarely addressed due to the intrinsic experimental complexity to control very low energy electrons. Furthermore, several results published in the past have been recently questioned, allegedly suffering from experimental systematics. Here, we critically review the experimental method used to study LE-SEY and precisely define the energy region in which the experimental data can be considered valid. By analyzing the significantly different behavior of LE-SEY in clean polycrystalline Cu (going toward zero at zero impinging energies) and in its as received technical counterpart (maintaining a significant value in the entire region), we solve most, if not all, of the apparent controversy present in the literature, producing important inputs for better understanding the device performances related to their LE-SEY. Simulations are then performed to address the impact of such results on electron cloud predictions in the LHC.