Recent progress of laser stripping POP demonstration study at J-PARC RCS

To realize the laser charge-exchange injection (LCEI) of H⁻ beam, a Proof-of-principle (POP) demonstration of 400 MeV H⁻ stripping to proton by using only lasers is under preparation at J-PARC RCS. The conventional H⁻ CEI done by using a stripper foil has serious issues associated with its short and unexpected lifetime as well as extremely high residual radiation caused by uncontrolled foil scattering beam losses. It is thus extremely difficult to realize a next generation proton accelerator with multi-MW beam power. The present method comprises three steps for an H⁻ stripping by using lasers. The H⁻ is first neutralized to H⁰ by an YAG laser, the H⁰ is then excited to an upper state (called H^0∗) by using a UV laser, which is finally stripped to proton by the YAG laser. The R&D of YAG laser system is in advanced stage and we have also developed a multi-reflection laser cavity system to significantly reduce the seed laser power, which was also tested for 3 MeV H⁻ beam neutralization. The R&D of the UV laser produced by higher harmonic generation from the YAG laser has also been started. The experimental studies for the POP demonstration will be started in 2022. (author)