On Thursday, June 2, an ion beam was accelerated through the beta=0.041 cryomodules for the first time at ReA, the reaccelerator at MSU.
ReA is a superconducting linac designed to accelerate rare isotope beams produced by NSCL’s Coupled Cyclotron Facility. ReA will provide the nuclear science community with a wide variety of exotic isotopes for nuclear science experiments at variable energies and high beam quality. When FRIB is completed, ReA will be part of the new facility and serve as its post accelerator.
In May, following successful beam acceleration through the first cryomodule, the commissioning effort continued through the second, six-cavity beta=0.041 cryomodule. A He+ beam from the pilot ion source was accelerated by the room temperature Radio Frequency Quadrupole (RFQ) to 0.6 MeV/u, then rebunched using the first SRF cryomodule and further accelerated by the second cryomodule to slightly above the design energy of 1.38 MeV/u. All six cavities performed above ReA specifications and have been operated 24 hours-a-day, 7 days-a-week for two weeks with phase and amplitude locked.
The kinetic energy of the accelerated beam particles after the second cryomodule was measured with a foil silicon detector. Figure 1 shows the energy spectrum of the accelerated beam using only the RFQ together with the spectrum obtained when one cavity after the other was turned on and phased for acceleration. Each cavity shifted the energy by about 0.53 MeV. The silicon detector was calibrated using the output energy of the RFQ and an off axis calibration source, which provided alpha particles at an energy of 5.5 MeV. The acceleration voltage of the cavities was chosen such that the final beam energy coincided with the energy of calibration source making the determination of the beam energy explicit.