R&D OF HELIUM GAS STRIPPER FOR INTENSE URANIUM BEAMS

Intensity upgrade of uranium beams is one of the main concerns at the RIKEN Radioactive Isotope Beam Factory (RIBF). The lifetime problem of carbon-foil strippers due to the high energy loss of uranium beams around 10 MeV/u was a principal bottleneck for the intensity upgrade in the acceleration scheme at the RIBF. We have developed a recirculating He-gas stripper as an alternative to carbon foils for the acceleration of high-power uranium beams. The new stripping system was actually operated in user runs with U 35+ beams of more than 1 puA. Electron-stripped U 64+ beams were stably delivered to subsequent accelerators without serious deterioration of the system for six weeks. The new He-gas stripper, which removed the primary bottleneck in the high-power uranium acceleration, greatly contributed to the tenfold increase of the average output intensity of the uranium beams in 2012 from the previous year.