Development of a Laser-based emittance monitor for negative hydrogen beams

To maximise the collision rate of CERN's Large Hadron Collider (LHC) the new injector LINAC4 has been commissioned. By accelerating an H- beam instead of protons, it aims to double the beam brightness. To achieve this, a precise knowledge of the transverse beam characteristics in terms of beam emittance is essential. This thesis work covers the development of a laser-based monitor to measure non-destructively the LINAC4 beam transverse profile and emittance. This includes the design and test of different prototypes and the final instrument design to be permanently installed at LINAC4. The instrument is based on stripping of electrons from negative hydrogen ions. By scanning a focused laser-beam through the H- beam, the profile can be reconstructed by detecting the detached electrons and the transverse emittance can be obtained by monitoring the H0 profiles for each laser position. The laser-system consists of a low-power laser-source and a fibre-optic transfer of the laser-beam to the interaction point with the H- beam. A diamond strip-detector was implemented to monitor the H0 signal. Prototype tests conducted at a 3 MeV and 12 MeV H- beam agreed within +/- 3% compared with conventional techniques. A second prototype deflecting the detached electrons by a dipole magnet and recoding their signal with a single-crystal diamond detector achieved an agreement of the recorded profiles within +/- 2%. The final instrument design combines electron and H0 detection and provides a simultaneous emittance and profile measurement in the horizontal and vertical planes with a resolution of < 75 µm and < 100 µrad. The non-destructive instrument shall be routinely operated for automated on-line monitoring of LINAC4's transverse beam parameters.