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Description
The Facility for Rare Isotope Beams (FRIB) is a heavy ion accelerator facility aiming to reach 400-kW primary beams, which will extend the heavy-ion accelerator power frontier by more than one order of magnitude. FRIB’s superconducting radio frequency (SRF) continuous-wave heavy-ion linear accelerator can accelerate all the ions up to uranium to energies above 200 MeV/u. The design beam power of 400 kW requires an intense beam, 8.4 particle μA or 5.25 x 10^13 ions/s in the case of uranium.
FRIB’s driver linac uses a charge stripper at a location where the beam energy reaches 17-20 MeV/u, to remove electrons from the primary beam ions, which increases the energy gain of the beam being accelerated, by approximately a factor of two. The linac was designed to accelerate multiple charge states of the stripped beam. But the charge states beyond the acceptance of the linac are intercepted by a device called the charge selector. These are the two main beam-intercepting devices in the FRIB linac.
The major challenges in these devices are ultra-high volumetric heat density and intense radiation damage. FRIB has two types of charge stripper: liquid lithium charge stripper and rotating carbon foil stripper. The liquid lithium stripper is for high power heavy ion beam operations to overcome the above challenges. The carbon stripper is still used for beam operations at the current beam power and will be a back-up of the lithium stripper in the future. The current charge selector uses positional and static slits made of Glidcop AL15. We plan to upgrade it to intercept higher beam power.
In this paper, we report the recent operational experiences of charge strippers and charge selector at FRIB. FRIB beam power has steadily increased from 1 kW to 5 kW since the commencement of user operations in May 2022. The carbon stripper and charge selector supported the recent 10 kW 36Ar and 48Ca beam tests conducted in July 2023.
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