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  1. Coupling impedance and wake functions for laminated structures with an application to the Fermilab Booster

    Macridin, Alexandru ; Spentzouris, Panagiotis ; Amundson, James ; ... - Physical Review Special Topics - Accelerators and Beams

  2. Surface characterization of Nb samples electropolished together with real superconducting rf accelerator cavities

    Geng, Rong -Li ; Tyagi, P. V. ; Hayano, Hitoshi ; ... - Physical Review Special Topics. Accelerators and Beams
    Here, we report the results of surface characterizations of niobium (Nb) samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris and the beam-pipe. Auger electron spectroscopy (AES) was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive X-ray for elemental analysis (SEM/EDX) was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples non-uniformly. Niobium oxide granulesmore » with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.« less

  3. Structural Analysis of the SHMS Cosine Theta Superconducting Dipole Force Collar

    Lassiter, Steven ; Brindza, Paul ; Fowler, Mike ; ... - IEEE Transactions on Applied Superconductivity
    Jefferson Laboratory is developing a set of innovative superconducting magnets for the 12 GeV upgrade in JLAB Hall C. Here, we will report on the finite element analysis (FEA) of the force collar for the Super High Momentum Spectrometer Cosine Theta Dipole magnet. The force collar is designed with an interference fit and intended to provide enough pressure after cool down to operating temperature to counteract Lorentz forces acting on the dipole coil during operation. By counteracting the Lorentz forces and keeping the coil pack in overall compression, movement of the coils is expected to be minimized. The dimensional geometrymore » of the cold mass is maintained in the commercial solid modeling code UG/I-DEAS while the magnetic field design is maintained in the commercial TOSCA code from Vector Fields. The three dimensional FEA was conducted in the commercial codes ANSYS and IDEAS. The method for converting the models and calculating the loads transferred to the structure is discussed. The results show the cold mass response to: force collar assembly preload, differential thermal contraction, and operational Lorentz loads. Evaluations are made for two candidate force collar materials and two candidate force collar designs.« less

  4. Impact Analysis for Candidate Space Reactor Core Concept Designs for Potential Criticality Study

    Kim, Seokho H. ; Flanagan, George - Nuclear Technology
    A hydrodynamics model has been developed to study extreme deformation of the space reactor system impacting on the ground with a high velocity. Two-dimensional geometry models for a monolithic core and a pinned core reactor have been developed with dynamic material models, including the material constitutive models and the equation-of-state models. Calculations have been performed for the reactor impacting onto dry sand at 230 and 150 m/s. A pinned core has a much larger fraction of gas volume in the reactor core and thus collapses faster than a monolithic core. The 150-m/s impact velocity case reveals that the gas coolantmore » channels survive in a monolithic core even though the reactor is massively deformed. In a pinned core, however, most of the gas coolant region collapses with intact or partially collapsed fission product gas cores that are protected by solid UO2 fuel. Sand density varies as it is being compressed. Generally, sand beneath the impacting reactor has a higher density as it is compressed. In addition to consideration of global criticality, it is necessary to investigate local criticality. Because of nonuniform distribution of the gas coolant channels in a deformed monolithic core for the 230-m/s impact velocity case, it may be possible to induce criticality locally in those regions where collapse is more severe. It is not straightforward to make an engineering judgment based solely on impact analysis regarding which core concept is more susceptible to criticality events. The current impact study reveals that a pinned core reactor collapses faster than a monolithic core reactor. A reactor that collapses faster is thought to be more susceptible to producing a criticality. However, a monolithic core reactor with much higher mass and kinetic energy develops much higher compaction in the dry sand beneath the reactor. This means that it is expected to better reflect fast neutrons from the bottom boundary where the sand density for a monolithic core impact becomes much higher than for a pinned core impact. It is strongly recommended that neutronics calculations be performed to determine the susceptibility of criticality for the massively deformed nuclear reactors including appropriate reflecting boundary conditions.« less
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