Transverse Emittance Measurement of a 2.5 MeV Proton Beam on LIPAc, IFMIF’s Prototype

IFMIF (International Fusion Materials Irradiation Fa-cility) is an accelerator-driven neutron source aiming at testing fusion reactor materials. Under the Broader Ap-proach Agreement, a 125 mA / 9 MeV CW deuteron accelerator called LIPAc (Linear IFMIF Prototype Accel-erator) is currently under installation and commissioning at Rokkasho, Japan, to validate the IFMIF accelerator. During the beam commissioning at 5 MeV which started in June 2018, the horizontal and vertical transverse emit-tance of a 2.5 MeV proton beam have been measured downstream of the RFQ for different machine configura-tions. Such measurements were done with an emittance measurement unit composed of slits defining a beamlet of 200 µm width, then of steerers and finally of a SEM grids monitor. In this paper, the process and the system are first described. The secondary electron emission of SEM-Grid wires is then estimated based on measure-ments and results are close to the usual rule of thumb. Finally, emittance measurements are presented and comparisons with beam dynamics simulations show good agreement.