FRIB is developing a new N-doping method with a simplified recipe. This recipe is called wet nitrogen doping, by adding nitric acid to the conventional EP acid. Nitrogen doping introduces impurities to the SRF surface, and reduces the BCS resistance by shortening the mean free path, which leads to a higher Qo. Conventional nitrogen doping, developed at FNAL and Jlab, requires a high-temperature treatment (900 ºC), and an additional light EP to remove the over-contaminated layer. This recipe produces a decreasing Qo at extremely low fields but successfully achieves high Qo performance up to 25 MV/m. The wet doping method does not require additional high-temperature baking and light EP afterwards, therefore it is superior in terms of processing steps. This method produced a high Qo of 8x10^10 at a low field of 0.5MV/m without the decreasing trend on FRIB beta=0.53 HWR. In this presentation, we will show the related R&D results generated from the FRIB 0.53 HWRs.

The superconducting (SC) driver linac for the Facility for Rare Isotope Beams (FRIB) includes 46 cryomodules for acceleration of heavy ions to 200 MeV per nucleon. FRIB cryomodules have been supporting sustainable and reliable delivery of high-power heavy ion beams, including 10 kW uranium beam, to the target for production of rare isotope beams to nuclear physics user experiments. The linac operates in continuous-wave mode for maximum utilization of beam from the ion source. A total of 104 quarter-wave resonators (QWRs; β=0.041 and 0.085; 80.5 MHz) equipped with stepper-motor frequency tuners and frictional mechanical dampers are operated at 4 K. A total of 220 half-wave resonators (HWRs; β=0.29 and 0.53; 322 MHz) equipped with pneumatic frequency tuners are operated at 2 K. We will present resonance control and phase stability performance as well as experience with tuner systems in linac operation. FRIB cavities are designed to be operated at a peak surface electric field of approximately 30 MV/m. We will present cavity field emission performance over the years of linac operation and discuss field emission reduction measures such as pulsed RF conditioning (presently in use) and plasma processing (in development). Automation of SC devices is a key aspect of efficient delivery of beams to users. We will present our experience with automation of SC devices such as start-up, shut-down, and fast recovery from an RF trip as well as performance tracking of linac SC devices.

The superconducting (SC) driver linac for the Facility for Rare Isotope Beams (FRIB) includes 46 cryomodules for acceleration of heavy ions to 200 MeV per nucleon. FRIB cryomodules have been supporting sustainable and reliable delivery of high-power heavy ion beams, including 10 kW uranium beam, to the target for production of rare isotope beams to nuclear physics user experiments. The linac operates in continuous-wave mode for maximum utilization of beam from the ion source. A total of 104 quarter-wave resonators (QWRs; β=0.041 and 0.085; 80.5 MHz) equipped with stepper-motor frequency tuners and frictional mechanical dampers are operated at 4 K. A total of 220 half-wave resonators (HWRs; β=0.29 and 0.53; 322 MHz) equipped with pneumatic frequency tuners are operated at 2 K. We will present resonance control and phase stability performance as well as experience with tuner systems in linac operation. FRIB cavities are designed to be operated at a peak surface electric field of approximately 30 MV/m. We will present cavity field emission performance over the years of linac operation and discuss field emission reduction measures such as pulsed RF conditioning (presently in use) and plasma processing (in development). Automation of SC devices is a key aspect of efficient delivery of beams to users. We will present our experience with automation of SC devices such as start-up, shut-down, and fast recovery from an RF trip as well as performance tracking of linac SC devices.

FRIB is developing a new N-doping method with a simplified recipe. This recipe is called wet nitrogen doping, by adding nitric acid to the conventional EP acid. Nitrogen doping introduces impurities to the SRF surface, and reduces the BCS resistance by shortening the mean free path, which leads to a higher Qo. Conventional nitrogen doping, developed at FNAL and Jlab, requires a high-temperature treatment (900 ºC), and an additional light EP to remove the over-contaminated layer. This recipe produces a decreasing Qo at extremely low fields but successfully achieves high Qo performance up to 25 MV/m. The wet doping method does not require additional high-temperature baking and light EP afterwards, therefore it is superior in terms of processing steps. This method produced a high Qo of 8x10^10 at a low field of 0.5MV/m without the decreasing trend on FRIB beta=0.53 HWR. In this presentation, we will show the related R&D results generated from the FRIB 0.53 HWRs.