FRIB, East Lansing, Michigan, USA
Fermilab, Batavia, Illinois, USA
INFN/LNL, Legnaro (PD), Italy
KEK, Ibaraki, Japan
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
IMP/CAS, Lanzhou, People's Republic of China
The Facility for Rare Isotope Beams (FRIB) is based upon a high power heavy ion driver linac under construction at Michigan State University under a cooperative agreement with the US DOE. The construction of conventional facilities already started in the summer, 2013, and the accelerator production began from the summer, 2014. FRIB will accelerate all the stable ion beams from proton to uranium beyond a beam energy of 200 MeV/u and up to a beam power of 400 kW to produce a great number of various rare isotopes using SRF linac. The FRIB SRF driver linac makes use of four kinds of SRF structures. Totally 332 two gap cavities and 48 cryomodules are needed. All SRF hardware components have been validated and are now moving to production. The SRF infrastructure also has been constructed in MSU campus. This talk will present FRIB project and challenges regarding SRF technologies. The status of SRF linac hardware validation and their production, SRF infrastructure status and plan shall be addressed. The information that can be relevant for future large scale proton/ion SRF linacs will also be provided.
MSU, East Lansing, Michigan, USA
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
Delamination cracks can form in rolled Nb sheets, and between layers with different micro-structures. Such cracks cause resistance to heat conduction from the RF surface to the liquid He bath. A delamination crack can negate the advances in manufacturing processes that have enhanced the thermal conductivity of Nb. Here, temperature excesses are calculated as functions of crack size and location, and the power dissipated at an imperfection in the RF surface. A disk shape of Nb sheet is modeled as having adiabatic sides. A hemispherical defect is located on the RF surface at the center of this section. A crack is modeled as a void within the Nb disk. The Kapitza resistance between the Nb surface and liquid He is varied. The results indicate that an incipient crack leads to a decrease in the magnetic flux required to cause thermal breakdown. The decrease in the field is gradual with increasing crack radius, until the crack radius nearly equals the section radius, after which the field required for breakdown decreases sharply. To a lesser extent, the field strength for thermal breakdown also decreases with increased crack depth.
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
ASC, Tallahassee, Florida, USA
NHMFL, Tallahassee, Florida, USA
When SRF cavity shapes are formed from Nb sheets, the metallurgical processing introduces microstructural defects such as dislocations and low-angle grain boundaries that can serve as pinning centers for magnetic flux that may degrade cavity performance. Therefore, the relationship between magnetic flux behavior and microstructural defects in carefully strained SRF Nb sheet was investigated. Laue X-ray and EBSD-OIM crystallographic analyses of large grain ingot slices were used to characterize microstructural defects and then predict which grains and sample orientations will produce desired model defects due to tensile deformation. Grain orientations were chosen to favor specific slip systems, which generate dislocations with special angles with respect to the sample surface. Nb bicrystals were also prepared to investigate the effects of grain boundaries on flux pinning. The generated defect structures were confirmed by OIM and TEM. Cryogenic magneto-optical imaging was used to directly observe the penetration of magnetic flux into the deformed Nb. These model samples have deformation that is similar to that expected in typical cavity forming processes.
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
MSU, East Lansing, Michigan, USA
High purity Nb has been used to build accelerator cavities over the past couple decades, and there is a growing interest in using ingot Nb as an alternative to the fine grain sheets. Plastic deformation governed by slip is complicated in body-centered cubic metals like Nb. Besides the crystal orientation with respect to the applied stress (Schmid effect), slip is also affected by other factors including temperature, strain rate, strain history, and non-Schmid effects such as twinning/anti-twinning asymmetry and non-glide shear stresses. A clear understanding of slip is an essential step towards modeling the deep drawing of large grain ingot slices, hence predicting the final microstructure/performance of cavities. Two groups of single crystals, with and without a prior heat treatment, were deformed to 40% engineering strain in uniaxial tension. Differences in flow stresses and active slip systems between the two groups were observed, likely due to the removal of preexisting dislocations. Crystal plasticity modeling of the stress-strain behavior suggests that the non-Schmid effect is small in Nb, and that the deep drawing process might be approximated with a Schmid model.
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
An understanding of the relationship between mechanical and functional properties, and processing history is essential in order to manufacture polycrystalline niobium cavities with consistent performance. The crystallographic texture (preferred crystal orientation) and microstructure in polycrystalline sheet varies considerably, so identifying its influence on properties is needed to achieve a better understanding of how to control properties of high purity niobium. Samples extracted from many lots produced by Tokyo Denkai and Ningxia sheet were examined. Through-thickness texture of the undeformed niobium samples was measured using electron backscattered pattern mapping. Texture is identified with pole figures, orientation distribution function, and grain misorientation relationships. Stress-strain tests were done to identify ultimate tensile stress, elongation, 0.2% yield strength, and hardening rate. From tests on many lots, there is no clear trend between the mechanical and material properties in high purity niobium and correlations between various microstructural and mechanical properties show significant scatter and few apparent correlations.
MSU, East Lansing, Michigan, USA
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
Deformation behavior of niobium (Nb) is not thoroughly studied, although it is widely used in manufacturing superconducting cavities. This deficiency of knowledge limits the predictibality in raw material properties for fine grain sheets, which are less anisotropic and easier to deform uniformly than large grain sheets. Studies on modeling and simulation of deformation of Nb are also limited. Therefore design of a new manufacturing procedure becomes a costly process, because models predicting the deformation of Nb are not accurate. A polycrystal is an aggregate of single crystals. Tensile tests were performed on single crystal with different orientations, to study the deformation behavior of Nb. A number of crystal plasticity models were developed, calibrated and finally used to predict the deformation of single crystal tensile samples. This study compares the predictions of these models. This provides a foundation for physically realistic polycrystal deformation models.
NSCL, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
Major work centers of the new SRF Highbay are fully installed and in use for FRIB pre-production SRF quarter-wave and half-wave resonators, including inspection area, high temperature vacuum furnace for cavity degassing, chemical etching facility and processing and assembly cleanrooms. Pre-production activities focus on optimizing workflow by reducing process time, tracking part status and related data, and identifying bottlenecks. Topics discussed may include; buffered chemical polish (BCP) etching for cavity frequency control, degassing time reduction, automated high pressure rinse, particle control against field emission, pre-production cavity test results and implementation of workflow status programs
FRIB, East Lansing, Michigan, USA
MSU, East Lansing, Michigan, USA
Michigan State University, East Lansing, Michigan, USA
FRIB, East Lansing, Michigan, USA
University of Nevada, Reno, Reno, Nevada, USA
Currently most of Niobium (Nb) cavities are manufactured from fine grain Nb sheets. As-cast ingots go through a series of steps including forging, milling, rolling, and intermediate annealing, before they are deep-drawn into a half-cell shape and subsequently electron beam welded to make a full cavity. Tube hydroforming, a manufacturing technique where a tube is deformed using a pressurized fluid, is an alternative to the current costly manufacturing process. A whole cavity can be made from a tube using tube hydroforming. This study focuses on deformation of large grain Nb tubes during hydroforming. The crystal orientation of the grains is recorded. The tube is marked with a square-circle-grid which is used to measure the strain after deformation. The deformation of the tube is going to be modeled with crystal plasticity finite element and compared with experiments. This paper only covers the characterization of the tube and the hydroforming process.
FRIB, East Lansing, Michigan, USA
INFN/LNL, Legnaro (PD), Italy
The driver linac for the Facility for Rare Isotope Beams (FRIB) will require the production of 48 cryomodules. FRIB has completed the fabrication and testing of a β=0.085 quarter-wave cryomodule as a pre-production prototype. This cryomodule qualified the performance of the resonators, fundamental power couplers, tuners, and cryogenic systems of the β=0.085 quarter-wave design. In addition to the successful systems qualification; the ReA6 cryomodule build also verified the FRIB bottom up assembly and alignment method. The lessons learned from the ReA6 cryomodule build, as well as valuable fabrication, sourcing, and assembly experience are applied to the design and fabrication of FRIB production cryomodules. This paper will report the results of the β=0.085 quarter-wave cryomodule testing, fabrication, and assembly; production implications to future cryomodules will also be presented. Authors: