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Romanenko A.,Fermi National Accelerator Laboratory | Grassellino A.,Fermi National Accelerator Laboratory | Barkov F.,Fermi National Accelerator Laboratory | Ozelis J.P.,Facility for Rare Isotope Beams
Physical Review Special Topics - Accelerators and Beams

The near-surface nanostructure of niobium determines the performance of superconducting microwave cavities. Subtle variations in surface nanostructure lead to yet unexplained phenomena such as the dependence of the quality factor of these resonating structures on the magnitude of rf fields - an effect known as the "Q slopes". Understanding and controlling the Q slopes is of great practical importance for particle accelerators. Here we investigate the mild baking effect - 120 C vacuum baking for 48 hours - which strongly affects the Q slopes. We used a hydrofluoric acid rinse alternating with oxidation in water as a tool for stepwise material removal of about 2 nanometers/step from the surface of superconducting niobium cavities. Applying removal cycles on mild baked cavities and measuring the quality factor dependence on the rf fields after one or several such cycles allowed us to explore the distribution of lossy layers within the first several tens of nanometers from the surface. We found that a single HF rinse results in the increase of the cavity quality factor. The low field Q slope was shown to be mostly controlled by the material structure within the first six nanometers from the surface. The medium field Q slope evolution was fitted using linear (â̂B peak surface magnetic field) and quadratic (â̂B2) terms in the surface resistance and it was found that best fits do not require the quadratic term. We found that about 10 nanometers of material removal are required to bring back the high field Q slope and about 20-50 nanometers to restore the onset field to the prebaking value. Source

Valverde A.A.,National Superconducting Cyclotron Laboratory | Valverde A.A.,Michigan State University | Bollen G.,Michigan State University | Brodeur M.,University of Notre Dame | And 17 more authors.
Physical Review Letters

We report the first direct measurement of the O14 superallowed Fermi β-decay QEC value, the last of the so-called "traditional nine" superallowed Fermi β decays to be measured with Penning trap mass spectrometry. O14, along with the other low-Z superallowed β emitter, C10, is crucial for setting limits on the existence of possible scalar currents. The new ground state QEC value, 5144.364(25) keV, when combined with the energy of the 0+ daughter state, Ex(0+)=2312.798(11)keV [F. Ajzenberg-Selove, Nucl. Phys. A523, 1 (1991)], provides a new determination of the superallowed β-decay QEC value, QEC(sa)=2831.566(28)keV, with an order of magnitude improvement in precision, and a similar improvement to the calculated statistical rate function f. This is used to calculate an improved Ft value of 3073.8(2.8) s. © 2015 American Physical Society. Source

Gupta R.,Brookhaven National Laboratory | Anerella M.,Brookhaven National Laboratory | Joshi P.,Brookhaven National Laboratory | Higgins J.,Brookhaven National Laboratory | And 4 more authors.
IEEE Transactions on Applied Superconductivity

This paper presents the design, construction, and test results of a high-energy-density coil for a superconducting magnetic energy storage system (SMES). The coil was designed to reach 25 T at 4 K in a 100-mm bore under a program funded by ARPA-E. The coil used over 6 km of 12-mm-wide second-generation high-temperature superconductors (HTS) provided by SuperPower. Such high fields and large aperture in a coil built with a new and still-developing conductor and magnet technology created several challenges, which included large stresses and quench protection. This paper summarizes an ambitious research program that resulted in an SMES coil reaching 12.5 T at 27 K. This is the first time that such high fields and such high energy densities have been generated at a temperature over 10 K, and it opens the door for the possible use of HTS magnets in energy storage and other applications. © 2016 IEEE. Personal use is permitted. Source

Martel I.,University of Huelva | Bontoiu C.,University of Huelva | Pomares M.J.R.,University of Huelva | Garbayo A.,AVS | Villari A.C.C.,Facility for Rare Isotope Beams
IPAC 2014: Proceedings of the 5th International Particle Accelerator Conference

A double frequency Electron Cyclotron Resonance Ion Source for the project LINCE (Linear European Center) in Huelva, Spain, is being designed for efficient production of high intensity ions from proton to Uranium. The magnetic design was optimized using three solenoid structures for axial and a dodecapole for radial confinement. Mechanical design studies were also initiated. Copyright © 2014 CC-BY-3.0 and by the respective authors. Source

Crawled News Article
Site: http://phys.org/physics-news/

Michigan State University researchers, working with colleagues from Technical University Darmstadt in Germany, are zeroing in on the answer to one of science's most puzzling questions: Where did heavy elements, such as gold, originate? Currently there are two candidates, neither of which are located on Earth - a supernova, a massive star that, in its old age, collapsed and then catastrophically exploded under its own weight; or a neutron-star merger, in which two of these small yet incredibly massive stars come together and spew out huge amounts of stellar debris. In a recently published paper in the journal Physical Review Letters, the researchers detail how they are using computer models to come closer to an answer. "At this time, no one knows the answer," said Witold Nazarewicz, a professor at the MSU-based Facility for Rare Isotope Beams and one of the co-authors of the paper. "But this work will help guide future experiments and theoretical developments." By using existing data, often obtained by means of high-performance computing, the researchers were able to simulate production of heavy elements in both supernovae and neutron-star mergers. "Our work shows regions of elements where the models provide a good prediction," said Nazarewicz, a Hannah Distinguished Professor of Physics who also serves as FRIB's chief scientist. "What we can do is identify the critical areas where future experiments, which will be conducted at FRIB, will work to reduce uncertainties of nuclear models." Other researchers included Dirk Martin and Almudena Arcones from Technical University Darmstadt and Erik Olsen of MSU. MSU is establishing FRIB as a new scientific user facility for the Office of Nuclear Physics in the U.S. Department of Energy Office of Science. Explore further: Researchers make precise measurements of the half-lives of previously unmeasured nuclei More information: D. Martin et al. Impact of Nuclear Mass Uncertainties on the Process , Physical Review Letters (2016). DOI: 10.1103/PhysRevLett.116.121101

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