Development of low pressure residual gas ionization profile monitor

Non-destructive profile monitor is a crucial beam-diagnostic device at Japan Proton Accelerator Research Complex (J-PARC) where the beams of 750 kW (50 GeV-15 μA) must be handled safely and stably since beam losses must be kept as low as possible for maintenance. We have developed Residual Gas Ionization Profile Monitor (RGIPM) operated in low pressure of 1 Pa, which is achieved with rotary pumps. The knock-on electrons produced by ionization of residual gas with beams are collected with electric and magnetic fields. Applying the magnetic field parallel to the electric field is essential to reduce diffusion by collisions of electrons with residual gas molecules. The prototype RGIPM installed in the slow-extraction beam lines at KEK 12 GeV Proton Synchrotron shows the good performances of profile measurement, position and intensity dependences, and so forth. The present article reports the experimental setup and the results of test experiments. (author)