Beam Position Detection of a Short Electron Bunch in Presence of a Longer and More Intense Proton Bunch for the AWAKE Experiment

The AWAKE experiment studies the acceleration of electrons to multi-GeV levels driven by the plasma wakefield generated by an ultra-relativistic and high intensity proton bunch. The proton beam, being considerably more intense than the co-propagating electron bunch, perturbs the measurement of the electron beam position achieved via standard techniques. This contribution shows that the electrons position monitoring is possible by frequency discrimination, exploiting the large bunch length difference between the electron and proton beams. Simulations and a beam measurement hint, the measurement has to be carried out in a frequency regime of a few tens of GHz, which is far beyond the spectrum produced by the 1ns long (4 σ Gaussian) proton bunch. As operating a conventional Beam Position Monitor (BPM) in this frequency range is problematic, an innovative approach based on the emission of coherent Cherenkov Diffraction Radiation (ChDR) in dielectrics is being studied. After describing the monitor concept and design, we will report about the results achieved with a prototype system at the CERN electron facility CLEAR.