LINAC4 Laser Profile and Emittance Meter Commissioning

The CERN LINAC4 is now equipped with two laser profile and emittance meters, a basically non destructive measurement of the transverse beam profile, not limited by the beam power density. The light of a pulsed laser is trans- ported through optical fibers and focused into the 160 MeV/c $H^{-}$ beam. The interaction of this laser “wire” with the $H^{-}$ ions detaches electrons that are collected by an electron- multiplier, while the resulting $H^0$ particles, after being separated from the main $H^{-}$ beam by a dipole magnet, are recorded by a diamond strip detector, located a few meters away from the interaction point. The transverse beam emittance and profile are reconstructed from the laser by a stepped scan through the $H^{-}$ beam. After several years of feasibility tests and prototyping, this paper presents the details about the final hardware implementation, operational aspects, and the 2022 experimental results.