Following its fifth Accelerator Readiness Review (ARR05) 21- 22 April, FRIB commissioned the entire linear accelerator (linac) on 25 April. The FRIB team commissioned a krypton-86 beam to 212 million electron-volts per nucleon (MeV/nucleon) using all 46 cryomodules, achieving 100-percent beam transmission in less than three hours on the first attempt. The commissioning team was distributed to five separate control rooms to comply with COVID-19 workplace safeguards.

Commissioning involves integrated testing of individual devices and beam commissioning of devices working together. Commissioning the entire linac means that all of its segments, including all 46 beam-accelerating cryomodules and four superconducting (SC) dipole magnets, are ready for operation.

The commissioning tasks also included:

• FRIB’s helium refrigeration system and cryogenic distribution system have been completed.
• All linac superconducting radiofrequency cryomodules and superconducting magnets have been cooled down, energized and ready for beam.
• All linac normal conducting devices are energized and ready for beam.
• Lithium and carbon charge strippers are co-existing for enhanced availability.

As FRIB prepares for operation, several stages of commissioning are conducted to demonstrate readiness of the different segments of the accelerator. Integrated testing examines the functionality of the system.

Leading up to the entire linac being commissioned, the first three cryomodules were commissioned in 2018, the first 15 in 2019; and 37 of 46 in 2020. The 2019 commissioning milestone marked FRIB becoming the world’s highest-energy continuous-wave hadron linear accelerator. The 2020 milestone marked FRIB demonstrating accelerator Key Performance Parameters required at project completion upon accelerating an argon-36 beam to 204 MeV/nucleon.

The linac’s beam-accelerating cryomodules contain superconducting radio frequency (SRF) resonators that accelerate the beam while operating at temperatures a few degrees above absolute zero. Much like a heavy truck, heavy ion beams speed up slowly starting from rest. The first three cryomodules in the linac accelerate the beam to 1 percent of FRIB’s final beam energy of 200 MeV/nucleon, the first 15 cryomodules to 10 percent, and the remaining 31 cryomodules provide the other 90 percent of FRIB’s final beam energy.

The next ARR (ARR06) is scheduled for fall 2021, on the path to the first FRIB experiments in 2022.