FRIB, East Lansing, USA
INFN/LNL, Legnaro (PD), Italy
The driver linac for the Facility for Rare Isotope Beams (FRIB) comprises four kinds of cavities (β=0.041, 0.085, 0.29, and 0.53) and six types of cryomodules including matching modules. FRIB has completed the fabrication and the cold test of a β=0.53 pre-production cryomodule, which is the first prototype for a half-wave (β=0.29 and 0.53) cavity. This paper describes the fabrication and the cold test result of the β=0.53 pre-production cryomodule including lessons learned.
FRIB, East Lansing, Michigan, USA
INFN/LNL, Legnaro (PD), Italy
KEK, Ibaraki, Japan
ANL, Argonne, Illinois, USA
TRIUMF, Vancouver, Canada
JLab, Newport News, Virginia, USA
The Facility for Rare Isotope Beams (FRIB), under construction at Michigan State University, will utilize a driver linac to accelerate stable ion beams from protons to uranium up to energies of >200 MeV per nucleon with a beam power of up to 400 kW. The FRIB linac consists of 46 cryomodules containing a total of 324 superconducting radio-frequency (SRF) resonators and 69 superconducting solenoids. The design of all six type cryomodules has been completed. The critical SRF components are tested as subsystem and validated in the pre-production cryomodules. The mass production of SRF cryomodules is underway. Here we report on the progress of the technical construction of FRIB superconducting linac.
FRIB, East Lansing, USA
Construction of a new accelerator for nuclear physics research, the Facility for Rare Isotope Beams (FRIB), is underway at Michigan State University (MSU). The FRIB linac will use superconducting resonators at an operating temperature of 2 K to accelerate ions to 200 MeV per nucleon. The linac requires 106 quarter wave resonators (80.5 MHz, β = 0.043 and 0.086) and 248 half wave resonators (322 MHz, β = 0.29 and 0.54), all made from sheet Nb. Production resonators being delivered to MSU by cavity vendors. At MSU, the resonators are etched, rinsed, and tested in MSU's certification test facility. Certification testing is done before the installation of the high-power input coupler and the tuner. After certification, the resonators are tested in the cryomodule before installation into the FRIB tunnel. The cryomodule test goals are to verify integrated operation of the resonators, RF couplers, tuners, RF controls, and superconducting solenoids. To date, 10 cryomodules out of 48 have been fabricated, and 8 of the cryomodules have been certified. Cryomodule test results are presented in this paper.
Michigan State University, East Lansing, Michigan, USA
NHMFL, Tallahassee, Florida, USA
ASC, Tallahassee, Florida, USA
FRIB, East Lansing, Michigan, USA
High purity Nb is commonly used for fabricating SRF cavities due to its high critical temperature and its formability. However, microstructural defects such as dislocations and grain boundaries in niobium can serve as favorable sites for pinning centers of magnetic flux that can degrade SRF cavity performance. In this study, two bi-crystal niobium samples extracted from strategically selected grain boundaries were investigated for the effect of grain misorientation on magnetic flux behavior. Laue X-ray and EBSD-OIM crystallographic analyses were used to characterize grain orientations and orientation gradients. Cryogenic Magneto-Optical Imaging (MOI) was used to directly observe magnetic flux penetration at about 5-8 K. Flux penetration was observed along one of the grain boundaries, as well as along a low angle boundary that was not detected prior to MOI imaging. Hydride scars on the sample surface after MOI were examined using atomic force microscopy (AFM) analysis. The relationships between dislocation content, cryo-cooling, flux penetration and grain boundaries are examined.
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
Although the quality factor of niobium cavities has improved, performance variability arises from microstructural defects such as dislocations and grain boundaries that can trap magnetic flux, block heat transfer, and perturb superconducting currents. Microstructural defect evolution is compared in four samples extracted from a 2.8 mm thick large-grain niobium slice, with tensile axes chosen to generate desired dislocation structures during deformation. The four samples are 1) as-extracted, 2) extracted and annealed, 3) extracted and then deformed to 40% strain, and 4) extracted, annealed at 800 °C 2 hours, and deformed to 40% strain. Electron Channeling Contrast Imaging (ECCI) was performed on all samples to characterize initial dislocation density, dislocation structure evolution due to annealing and deformation, and related to the mechanical behavior observed in stress-strain curves. The orientation evolution and geometrically necessary dislocation (GND) density were characterized with electron backscattered diffraction (EBSD) maps. Fundamental understanding of dislocation evolution in niobium is necessary to develop models for computational cavity design.
FRIB, East Lansing, Michigan, USA