Experimental results of the laserwire emittance scanner for LINAC4 at CERN

Within the framework of the LHC Injector Upgrade (LIU), the new LINAC4 is currently being commissioned to replace the existing LINAC2 proton source at CERN. After the expected completion at the end of 2016, the LINAC4 will accelerate H⁻ ions to 160 MeV. To measure the transverse emittance of the H⁻ beam, a method based on photo-detachment is proposed. This system will operate using a pulsed laser with light delivered via an optical fibre and subsequently focused onto the H⁻ beam. The laser photons have sufficient energy to detach the outer electron and create H⁰/e⁻ pairs. In a downstream dipole, the created H⁰ particles are separated from the unstripped H⁻ ions and their distribution is measured with a dedicated detector. By scanning the focused laser beam across the H⁻ beam, the transverse emittance of the H⁻ beam can be reconstructed. This paper will first discuss the concept, design and simulations of the laser emittance scanner and then present results from a prototype system used during the 12 MeV commissioning of the LINAC4.