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Sample records for niobium superconducting strip

  1. Superconductive niobium films coating carbon nanotube fibers

    NASA Astrophysics Data System (ADS)

    Salvato, M.; Lucci, M.; Ottaviani, I.; Cirillo, M.; Behabtu, N.; Young, C. C.; Pasquali, M.; Vecchione, A.; Fittipaldi, R.; Corato, V.

    2014-11-01

    Superconducting niobium (Nb) has been successfully obtained by sputter deposition on carbon nanotube fibers. The transport properties of the niobium coating the fibers are compared to those of niobium thin films deposited on oxidized Si substrates during the same deposition run. For niobium films with thicknesses above 300 nm, the niobium coating the fibers and the thin films show similar normal state and superconducting properties with critical current density, measured at T = 4.2 K, of the order of 105 A cm-2. Thinner niobium layers coating the fibers also show the onset of the superconducting transition in the resistivity versus temperature dependence, but zero resistance is not observed down to T = 1 K. We evidence by scanning electron microscopy (SEM) and current-voltage measurements that the granular structure of the samples is the main reason for the lack of true global superconductivity for thicknesses below 300 nm.

  2. Superconducting structure with layers of niobium nitride and aluminum nitride

    DOEpatents

    Murduck, James M.; Lepetre, Yves J.; Schuller, Ivan K.; Ketterson, John B.

    1989-01-01

    A superconducting structure is formed by depositing alternate layers of aluminum nitride and niobium nitride on a substrate. Deposition methods include dc magnetron reactive sputtering, rf magnetron reactive sputtering, thin-film diffusion, chemical vapor deposition, and ion-beam deposition. Structures have been built with layers of niobium nitride and aluminum nitride having thicknesses in a range of 20 to 350 Angstroms. Best results have been achieved with films of niobium nitride deposited to a thickness of approximately 70 Angstroms and aluminum nitride deposited to a thickness of approximately 20 Angstroms. Such films of niobium nitride separated by a single layer of aluminum nitride are useful in forming Josephson junctions. Structures of 30 or more alternating layers of niobium nitride and aluminum nitride are useful when deposited on fixed substrates or flexible strips to form bulk superconductors for carrying electric current. They are also adaptable as voltage-controlled microwave energy sources.

  3. Superconducting structure with layers of niobium nitride and aluminum nitride

    DOEpatents

    Murduck, J.M.; Lepetre, Y.J.; Schuller, I.K.; Ketterson, J.B.

    1989-07-04

    A superconducting structure is formed by depositing alternate layers of aluminum nitride and niobium nitride on a substrate. Deposition methods include dc magnetron reactive sputtering, rf magnetron reactive sputtering, thin-film diffusion, chemical vapor deposition, and ion-beam deposition. Structures have been built with layers of niobium nitride and aluminum nitride having thicknesses in a range of 20 to 350 Angstroms. Best results have been achieved with films of niobium nitride deposited to a thickness of approximately 70 Angstroms and aluminum nitride deposited to a thickness of approximately 20 Angstroms. Such films of niobium nitride separated by a single layer of aluminum nitride are useful in forming Josephson junctions. Structures of 30 or more alternating layers of niobium nitride and aluminum nitride are useful when deposited on fixed substrates or flexible strips to form bulk superconductors for carrying electric current. They are also adaptable as voltage-controlled microwave energy sources. 8 figs.

  4. Dissipative hydride precipitates in superconducting niobium cavities

    SciTech Connect

    Romanenko, A.; Cooley, L.D.; Ciovati, G.; Wu, G.; /Argonne

    2011-10-01

    We report the first direct observation of the microstructural features exhibiting RF losses at high surface magnetic fields of above 100 mT in field emission free superconducting niobium cavities. The lossy areas were identified by advanced thermometry. Surface investigations using different techniques were carried out on cutout samples from lossy areas and showed the presence of dendritic niobium hydrides. This finding has possible implications to the mechanisms of RF losses in superconducting niobium at all field levels.

  5. Degreasing and cleaning superconducting RF Niobium cavities

    SciTech Connect

    Rauchmiller, Michael; Kellett, Ron; /Fermilab

    2011-09-01

    The purpose and scope of this report is to detail the steps necessary for degreasing and cleaning of superconducting RF Niobium cavities in the A0 clean room. It lists the required equipment and the cleaning procedure.

  6. Developing of superconducting niobium cavities for accelerators

    NASA Astrophysics Data System (ADS)

    Pobol, I. L.; Yurevich, S. V.

    2015-11-01

    The results of a study of structure and mechanical properties of welding joints, superconducting characteristics of the material after joining of welded components of superconducting radio frequency cavities are presented. The paper also describes the results of testing of the RF 1.3 GHz single-cell niobium cavity manufactured in the PTI NAS Belarus.

  7. Electroplating and stripping copper on molybdenum and niobium

    NASA Technical Reports Server (NTRS)

    Power, J. L.

    1978-01-01

    Molybdenum and niobium are often electroplated and subsequently stripped of copper. Since general standard plating techniques produce poor quality coatings, general procedures have been optimized and specified to give good results.

  8. Research & Development on Superconducting Niobium Materials via Magnetic Measurements

    SciTech Connect

    S. B. Roy, V. C. Sahni, and G. R. Myneni

    2011-03-01

    We present a study of superconducting properties of both large grain (1 mm average grain size) and small grain (50 micron average grain size) Niobium materials containing varying amounts of Tantalum impurities that have been used in the fabrication of high accelerating gradient superconducting radio frequency cavities. We found that a buffered chemical polishing of these Niobium samples causes a distinct reduction in the superconducting parameters like TC, wt- ppm to 1300 wt-ppm. Implications of these results on the performance of niobium superconducting radio frequency cavities are discussed, especially the anomalous high field RF losses that have been reported in the literature.

  9. Method for etching thin films of niobium and niobium-containing compounds for preparing superconductive circuits

    DOEpatents

    Kampwirth, Robert T.; Schuller, Ivan K.; Falco, Charles M.

    1981-01-01

    An improved method of preparing thin film superconducting electrical circuits of niobium or niobium compounds in which a thin film of the niobium or niobium compound is applied to a nonconductive substrate, and covered with a layer of photosensitive material. The sensitive material is in turn covered with a circuit pattern exposed and developed to form a mask of the circuit in photoresistive material on the surface of the film. The unmasked excess niobium film is removed by contacting the substrate with an aqueous etching solution of nitric acid, sulfuric acid and hydrogen fluoride, which will rapidly etch the niobium compound without undercutting the photoresist. A modification of the etching solution will permit thin films to be lifted from the substrate without further etching.

  10. Superconducting niobium thin film slow-wave structures

    NASA Technical Reports Server (NTRS)

    Bautista, J. J.; Petty, S. M.; Allen, L. H.; Beasley, M. R.; Hammond, R. H.

    1983-01-01

    A superconducting comb structure as a slow-wave element in a traveling-wave maser will significantly improve maser noise temperature and gain by reducing the insertion loss. The results of the insertion loss measurements of superconducting niobium slow-wave structures subjected to maser operating conditions at X-Band frequencies are presented.

  11. Superconducting nano-strip particle detectors

    NASA Astrophysics Data System (ADS)

    Cristiano, R.; Ejrnaes, M.; Casaburi, A.; Zen, N.; Ohkubo, M.

    2015-12-01

    We review progress in the development and applications of superconducting nano-strip particle detectors. Particle detectors based on superconducting nano-strips stem from the parent devices developed for single photon detection (SSPD) and share with them ultra-fast response times (sub-nanosecond) and the ability to operate at a relatively high temperature (2-5 K) compared with other cryogenic detectors. SSPDs have been used in the detection of electrons, neutral and charged ions, and biological macromolecules; nevertheless, the development of superconducting nano-strip particle detectors has mainly been driven by their use in time-of-flight mass spectrometers (TOF-MSs) where the goal of 100% efficiency at large mass values can be achieved. Special emphasis will be given to this case, reporting on the great progress which has been achieved and which permits us to overcome the limitations of existing mass spectrometers represented by low detection efficiency at large masses and charge/mass ambiguity. Furthermore, such progress could represent a breakthrough in the field. In this review article we will introduce the device concept and detection principle, stressing the peculiarities of the nano-strip particle detector as well as its similarities with photon detectors. The development of parallel strip configuration is introduced and extensively discussed, since it has contributed to the significant progress of TOF-MS applications.

  12. Manufacture of superconducting niobium cavity parts by hydropercussion punching

    NASA Astrophysics Data System (ADS)

    Azaryan, N. S.; Shirkov, G. D.; Zhurauski, A. Yu.; Petrakovski, V. S.; Batouritski, M. A.

    2016-03-01

    A complete cycle of manufacturing all parts of superconducting niobium cavities which comprise two half-cells, two drift tubes, and two flanges each has been developed. The cavity half-cells are manufactured by hydropercussion punching, which has a number of advantages over the instrumental stamping technique. For the first time, the diagram of formability of ultrapure niobium has been experimentally obtained for hydropercussion punching and the key parameters of the process have been determined that ensure complete deep-drawing of workpieces, viz., the value of the limit drawing ratio of ultrapure niobium that is 1.92 at a specific impact energy of 0.42 MJ/m2. The deviations of the half-cell dimensions from the rated values do not exceed 0.1 mm. Production tools required for all manufacturing steps have been created. The parameters of machining of the niobium cavity parts prior to welding have been experimentally established.

  13. Stress dependent oxidation of sputtered niobium and effects on superconductivity

    NASA Astrophysics Data System (ADS)

    David Henry, M.; Wolfley, Steve; Monson, Todd; Clark, Blythe G.; Shaner, Eric; Jarecki, Robert

    2014-02-01

    We report on the suppression of room temperature oxidation of DC sputtered niobium films and the effects upon the superconductive transition temperature, Tc. Niobium was sputter-deposited on silicon dioxide coated 150 mm wafers and permitted to oxidize at room temperature and pressure for up to two years. Resistivity and stress measurements indicate that tensile films greater than 400 MPa resist bulk oxidation with measurements using transmission electron microscope, electron dispersive X-ray spectroscopy, x-ray photoelectric spectroscopy, and secondary ion mass spectrometry confirming this result. Although a surface oxide, Nb2O5, consumed the top 6-10 nm, we measure less than 1 at. % oxygen and nitrogen in the bulk of the films after the oxidation period. Tc measurements using a SQUID magnetometer indicate that the tensile films maintained a Tc approaching the dirty superconductive limit of 8.4 K after two years of oxidation while maintaining room temperature sheet resistance. This work demonstrates that control over niobium film stress during deposition can prevent bulk oxidation by limiting the vertical grain boundaries ability to oxidize, prolonging the superconductive properties of sputtered niobium when exposed to atmosphere.

  14. Stress dependent oxidation of sputtered niobium and effects on superconductivity

    SciTech Connect

    David Henry, M. Wolfley, Steve; Monson, Todd; Clark, Blythe G.; Shaner, Eric; Jarecki, Robert

    2014-02-28

    We report on the suppression of room temperature oxidation of DC sputtered niobium films and the effects upon the superconductive transition temperature, T{sub c}. Niobium was sputter-deposited on silicon dioxide coated 150 mm wafers and permitted to oxidize at room temperature and pressure for up to two years. Resistivity and stress measurements indicate that tensile films greater than 400 MPa resist bulk oxidation with measurements using transmission electron microscope, electron dispersive X-ray spectroscopy, x-ray photoelectric spectroscopy, and secondary ion mass spectrometry confirming this result. Although a surface oxide, Nb{sub 2}O{sub 5}, consumed the top 6–10 nm, we measure less than 1 at. % oxygen and nitrogen in the bulk of the films after the oxidation period. T{sub c} measurements using a SQUID magnetometer indicate that the tensile films maintained a T{sub c} approaching the dirty superconductive limit of 8.4 K after two years of oxidation while maintaining room temperature sheet resistance. This work demonstrates that control over niobium film stress during deposition can prevent bulk oxidation by limiting the vertical grain boundaries ability to oxidize, prolonging the superconductive properties of sputtered niobium when exposed to atmosphere.

  15. America's Overview of Superconducting Science and Technology of Ingot Niobium

    SciTech Connect

    Gianluigi Ciovati, Peter Kneisel, Ganapati Myneni

    2011-03-01

    This contribution will present an overview of the results from R&D programs in the USA over the past four years towards the development of ingot Niobium as a viable alternative material to fabricate SRF cavities for particle accelerators. Activities at several laboratories and universities include fabrication, surface treatment and RF testing of single- and multi-cell cavities and studies of the thermal, mechanical and superconducting properties of samples from ingots of different purity. Possible advantages of ingot niobium over standard fine-grain (ASTM 6) are discussed and a streamlined treatment procedure to fully exploit those advantages is proposed.

  16. A spiraled niobium tin superconductive ribbon

    NASA Technical Reports Server (NTRS)

    Coles, W. D.

    1973-01-01

    Copper film is vapor-deposited on clean ribbon and sprayed with photosensitive etch-resistant material. Photographic film masks are placed on ribbon and exposed to ultraviolet light. Etchant removes copper and exposure to oxidizing atmosphere forms niobium oxide. Photosensitive material is removed and ribbon is immersed in molten temperatures.

  17. Niobium-based superconducting nano-device fabrication using all-metal suspended masks

    NASA Astrophysics Data System (ADS)

    Samaddar, S.; van Zanten, D.; Fay, A.; Sacépé, B.; Courtois, H.; Winkelmann, C. B.

    2013-09-01

    We report a novel method for the fabrication of superconducting nano-devices based on niobium. The well-known difficulties of lithographic patterning of high-quality niobium are overcome by replacing the usual organic resist mask by a metallic one. The quality of the fabrication procedure is demonstrated by the realization and characterization of long and narrow superconducting lines and niobium-gold-niobium proximity SQUIDs.

  18. Superconducting DC and RF Properties of Ingot Niobium

    SciTech Connect

    Pashupati Dhakal, Gianluigi Ciovati, Peter Kneisel, Ganapati Rao Myneni

    2011-07-01

    The thermal conductivity, DC magnetization and penetration depth of large-grain niobium hollow cylindrical rods fabricated from ingots, manufactured by CBMM subjected to chemical and heat treatment were measured. The results confirm the influence of chemical and heat-treatment processes on the superconducting properties, with no significant dependence on the impurity concentrations in the original ingots. Furthermore, RF properties, such as the surface resistance and quench field of the niobium rods were measured using a TE{sub 011} cavity. The hollow niobium rod is the center conductor of this cavity, converting it to a coaxial cavity. The quench field is limited by the critical heat flux through the rods' cooling channel.

  19. Improvement in bias current redistribution in superconducting strip ion detectors with parallel configuration

    NASA Astrophysics Data System (ADS)

    Nobuyuki, Zen; Go, Fujii; Shigetomo, Shiki; Masahiro, Ukibe; Masaki, Koike; Masataka, Ohkubo

    2015-09-01

    In time-of-flight mass spectrometry (TOF MS), superconducting strip ion detectors (SSIDs) in the parallel configuration are promising for ideal ion detection with a nanosecond-scale time response and a practical large sensitive area. In the parallel configuration, the bias current in one strip is diverted into other parallel strips after each detection event. Under high bias current conditions, the diverted bias current induces cascade switching of all parallel strips. Studies show that cascade switching degrades the ion count rate of SSIDs made from niobium and hence is disliked in TOF MS applications. To suppress the bias current redistribution, we connected resistors in a series with the individual parallel strips using aluminum-bonding wires. Their effect was studied by measuring the pulse height distributions. Project supported by a Grant-in-Aid for Scientific Research (A) and (C) from the Japan Society for the Promotion of Science (Grant Nos. 22246056 and 24619013).

  20. Structure and texture of electrolytic superconducting coatings of high-purity niobium

    NASA Astrophysics Data System (ADS)

    Kolosov, V. N.; Shevyrev, A. A.

    2014-08-01

    Modes of epitaxial growth of electrolytic superconducting coatings of high-purity niobium on substrates of niobium, molybdenum, and tungsten have been investigated. The dynamics of changes in the structure and texture of the coatings depending on the method of treatment of substrates, cathode current density, and thickness of the deposited niobium layer has been studied.

  1. A bulk niobium superconducting quarter wave resonator

    SciTech Connect

    Ben-Zvi, I. ); Chiaveri, E. ); Elkonin, B.V. ); Facco, A.; Sokolowski, J.S. . Lab. Nazionale di Legnaro)

    1990-01-01

    A bath-cooled all-niobium 160 MHz quarter wave resonator prototype was constructed and tested. The objective of this research has been the development of a high performance accelerating element with {beta}{sub opt} {approx equal} 0.11 for the ALPI linac at the Laboratori Nazionali di Legnaro. The design of this resonator was based upon a previous 150 MHz model, with minor changes due to the different frequency and to modified welding procedure. An accelerating field of 5 MV/m was achieved at a power dissipation of 10 W and the low power Q was 2.4 {times} 10{sup 8}. The resonator could dissipate 70 W of power without thermal breakdown. 16 refs., 2 figs., 1 tab.

  2. High-Q superconducting niobium cavities for gravitational wave detectors

    NASA Astrophysics Data System (ADS)

    de Paula, L. A. N.; Furtado, S. R.; Aguiar, O. D.; Oliveira, N. F., Jr.; Castro, P. J.; Barroso, J. J.

    2014-10-01

    The main purpose of this work is to optimize the electric Q-factor of superconducting niobium klystron cavities to be used in parametric transducers of the Mario Schenberg gravitational wave detector. Many cavities were manufactured from niobium with relatively high tantalum impurities (1420 ppm) and they were cryogenically tested to determine their resonance frequencies, unloaded electrical quality factors (Q0) and electromagnetic couplings. These cavities were closed with a flat niobium plate with tantalum impurities below 1000 ppm and an unloaded electrical quality factors of the order of 105 have been obtained. AC conductivity of the order of 1012 S/m has been found for niobium cavities when matching experimental results with computational simulations. These values for the Q-factor would allow the detector to reach the quantum limit of sensitivity of ~ 10-22 Hz-1/2 in the near future, making it possible to search for gravitational waves around 3.2 kHz. The experimental tests were performed at the laboratories of the National Institute for Space Research (INPE) and at the Institute for Advanced Studies (IEAv - CTA).

  3. Cathodic arc grown niobium films for RF superconducting cavity applications

    NASA Astrophysics Data System (ADS)

    Catani, L.; Cianchi, A.; Lorkiewicz, J.; Tazzari, S.; Langner, J.; Strzyzewski, P.; Sadowski, M.; Andreone, A.; Cifariello, G.; Di Gennaro, E.; Lamura, G.; Russo, R.

    2006-07-01

    Experimental results on the characterization of the linear and non-linear microwave properties of niobium film produced by UHV cathodic arc deposition are presented. Surface impedance Zs as a function of RF field and intermodulation distortion (IMD) measurement have been carried out by using a dielectrically loaded resonant cavity operating at 7 GHz. The experimental data show that these samples have a lower level of intrinsic non-linearities at low temperature and low circulating power in comparison with Nb samples grown by sputtering. These results make UHV cathodic arc deposition a promising technique for the improvement of RF superconducting cavities for particle accelerators.

  4. Method of manufacturing a niobium-aluminum-germanium superconductive material

    DOEpatents

    Wang, John L.; Pickus, Milton R.; Douglas, Kent E.

    1980-01-01

    A method for manufacturing flexible Nb.sub.3 (Al,Ge) multifilamentary superconductive material in which a sintered porous niobium compact is infiltrated with an aluminum-germanium alloy and thereafter deformed and heat treated in a series of steps at different successively higher temperatures preferably below 1000.degree. C. to produce filaments composed of Nb.sub.3 (Al,G3) within the compact. By avoiding temperatures in excess of 1000.degree. C. during the heat treatment, cladding material such as copper can be applied to facilitate a deformation step preceding the heat treatment and can remain in place through the heat treatment to also serve as a temperature stabilizer for supeconductive material produced. Further, these lower heat treatment temperatures favor formation of filaments with reduced grain size and, hence with more grain boundaries which in turn increase the current-carrying capacity of the superconductive material.

  5. Development of a superconducting connection for niobium cavities

    SciTech Connect

    Peter Kneisel; Gianluigi Ciovati; Jacek Sekutowicz; Waldemar Singer; Xenia Singer; Axel Matheisen

    2007-06-18

    Several, partially successful attempts have been made in the past to develop a superconducting connection between adjacent niobium cavities with the capability to carry up to 30 mT of the magnetic flux. Such a connection would be particularly of great benefit to layouts of long accelerators like ILC because it would shorten the distances between structures and therefore the total length of an accelerator with the associated cost reductions. In addition the superconducting connection would be ideal for a super-structure – two multi-cell cavities connected through a half wavelength long beam pipe providing the coupling. Two welded prototypes of super-structure have been successfully tested with the beam at DESY. The chemical treatment and water rinsing was rather complicated for these prototypes because of the length of the assembly. We have engaged in a program to develop such a connection, initially based on the Nb55Ti material. Several options are pursued such as e.g. a two-cell cavity is being used to explore the reachable magnetic flux for the TESLA like connection with a squeezed niobium gasket between the flanges. Other materials, such as NbZr or NbN are also being considered. In this contribution, we will report about the progress of our investigations.

  6. Development of a superconducting connection for niobium cavities

    SciTech Connect

    Peter Kneisel; Gianluigi Ciovati; Jacek Sekutowicz; Waldemar Singer; Xenia Singer; Axel Matheisen

    2007-06-22

    Several, partially successful attempts have been made in the past to develop a superconducting connection between adjacent niobium cavities with the capability to carry up to 30 mT of the magnetic flux. Such a connection would be particularly of great benefit to layouts of long accelerators like ILC because it would shorten the distances between structures and therefore the total length of an accelerator with the associated cost reductions. In addition the superconducting connection would be ideal for a super-structure – two multi-cell cavities connected through a half wavelength long beam pipe providing the coupling. Two welded prototypes of super-structure have been successfully tested with the beam at DESY. The chemical treatment and water rinsing was rather complicated for these prototypes because of the length of the assembly. We have engaged in a program to develop such a connection, initially based on the Nb55Ti material. Several options are pursued such as e.g. a two-cell cavity is being used to explore the reachable magnetic flux for the TESLA like connection with a squeezed niobium gasket between the flanges. Other materials, such as NbZr or NbN are also being considered. In this contribution, we will report about the progress of our investigations.

  7. Suppressed Superconductivity on the Surface of Superconducting RF Quality Niobium for Particle Accelerating Cavities

    SciTech Connect

    Sung, Z. H.; Polyanskii, A. A.; Lee, P. J.; Gurevich, A.; Larbalestier, D. C.

    2011-03-31

    Significant performance degradation of superconducting RF (radio frequency) niobium cavities in high RF field is strongly associated with the breakdown of superconductivity on localized multi-scale surface defects lying within the 40 nm penetration depth. These defects may be on the nanometer scale, like grain boundaries and dislocations or even at the much larger scale of surface roughness and welding pits. By combining multiple superconducting characterization techniques including magneto-optical (MO) imaging and direct transport measurement with non-contact characterization of the surface topology using scanning confocal microscopy, we were able to show clear evidence of suppression of surface superconductivity at chemically treated RF-quality niobium. We found that pinning of vortices along GBs is weaker than pinning of vortices in the grains, which may indicate suppressed superfluid density on GBs. We also directly measured the local magnetic characteristics of BCP-treated Nb sample surface using a micro-Hall sensor in order to further understanding of the effect of surface topological features on the breakdown of superconducting state in RF mode.

  8. Surface characterization of niobium for superconducting RF cavities

    NASA Astrophysics Data System (ADS)

    Cao, Chaoyue

    Surface characterization techniques including point contact tunneling (PCT) spectroscopy and Raman spectroscopy have been employed to study the surface of niobium (Nb) superconducting radio frequency (SRF) cavities. PCT spectroscopy provides a direct means of measuring the surface superconductivity, which is closely correlated with the cavity's performance characterized by the quality factor Q. Cavities with remarkably high Q show near ideal tunneling spectra with sharp coherent peaks and low zero bias conductance, consistent with the Bardeen-Cooper-Schrieffer (BCS) density of stats (DOS), and bulk gap parameter, Delta = 1.55-1.6 meV. Cavities with Q-drop often exhibit strong non-uniform heating during RF operations, with high loss regions identified as hot spots. PCT spectra on hot spots reveal suppressed superconductivity, broadened DOS and Kondo tunneling, consistent with magnetic impurities on the surface. Raman spectra on hot spots indicate the presence of various impurities on the surface including amorphous carbon, C-H chain compounds and NbC, providing insights into the formation of hot spots. The origin of the impurities is unclear at present but it is suggested that particular processing steps in SRF cavity fabrication may be responsible.

  9. High-gradient, pulsed operation of superconducting niobium cavities

    SciTech Connect

    Campisi, I.E.; Farkas, Z.D.

    1984-02-01

    Tests performed on several Niobium TM/sub 010/ cavities at frequencies of about 2856 MHz using a high-power, pulsed method indicate that, at the end of the charging pulse, peak surface magnetic fields of up to approx. 1300 Oe, corresponding to a peak surface electric field of approx. 68 MV/m, can be reached at 4.2/sup 0/K without appreciable average losses. Further studies of the properties of superconductors under pulsed operation might shed light on fundamental properties of rf superconductivity, as well as lead to the possibility of applying the pulse method to the operation of high-gradient linear colliders. 7 references, 30 figures, 2 tables.

  10. Temperature Mapping of Nitrogen-doped Niobium Superconducting Radiofrequency Cavities

    SciTech Connect

    Makita, Junki; Ciovati, Gianluigi; Dhakal, Pashupati

    2015-09-01

    It was recently shown that diffusing nitrogen on the inner surface of superconducting radiofrequency (SRF) cavities at high temperature can improve the quality factor of the niobium cavity. However, a reduction of the quench field is also typically found. To better understand the location of rf losses and quench, we used a thermometry system to map the temperature of the outer surface of ingot Nb cavities after nitrogen doping and electropolishing. Surface temperature of the cavities was recorded while increasing the rf power and also during the quenching. The results of thermal mapping showed no precursor heating on the cavities and quenching to be ignited near the equator where the surface magnetic field is maximum. Hot-spots at the equator area during multipacting were also detected by thermal mapping.

  11. Synthesis and characterization of superconducting nanocrystalline niobium nitride.

    PubMed

    Shi, Liang; Gu, Yunle; Chen, Luyang; Yang, Zeheng; Ma, Jianhua; Qian, Yitai

    2005-02-01

    Nanocrystalline niobium nitride (NbN0.9) was successfully synthesized at 600 degrees C through a solid-state reaction. The synthesis was carried out in an autoclave by using NbCl5 and NaN3 as the reactants. The X-ray powder diffraction pattern indicates the formation of cubic NbN0.9. Transmission electron microscopy images show that typical NbN0.9 crystallites are composed of uniform particles with an average size of about 30 nm and nanorod crystallites with a typical size of about 40 x 2500 nm. Magnetic measurements exhibited that a superconducting transition occurred at 15.4 K for the NbN0.9 product. PMID:15853151

  12. Method of nitriding niobium to form a superconducting surface

    DOEpatents

    Kelley, Michael J.; Klopf, John Michael; Singaravelu, Senthilaraja

    2014-08-19

    A method of forming a delta niobium nitride .delta.-NbN layer on the surface of a niobium object including cleaning the surface of the niobium object; providing a treatment chamber; placing the niobium object in the treatment chamber; evacuating the chamber; passing pure nitrogen into the treatment chamber; focusing a laser spot on the niobium object; delivering laser fluences at the laser spot until the surface of the niobium object reaches above its boiling temperature; and rastering the laser spot over the surface of the niobium object.

  13. High performance superconducting radio frequency ingot niobium technology for continuous wave applications

    SciTech Connect

    Dhakal, Pashupati Ciovati, Gianluigi Myneni, Ganapati R.

    2015-12-04

    Future continuous wave (CW) accelerators require the superconducting radio frequency cavities with high quality factor and medium accelerating gradients (≤20 MV/m). Ingot niobium cavities with medium purity fulfill the specifications of both accelerating gradient and high quality factor with simple processing techniques and potential reduction in cost. This contribution reviews the current superconducting radiofrequency research and development and outlines the potential benefits of using ingot niobium technology for CW applications.

  14. Thickness dependence of fracture behaviour in a superconducting strip

    NASA Astrophysics Data System (ADS)

    Yong, H. D.; Xue, C.; Zhou, Y. H.

    2013-05-01

    When subjected to a magnetic field, a superconducting strip will undergo an electromagnetic body force induced by flux pinning. The magnitude of the body force is dependent on the critical current density. It is well known that the critical current density in the strip will decrease with increasing thickness. In addition, the mechanical behaviour of the strip will also be affected by the thickness of the strip. Thus, the strip thickness has an influence on both the electromagnetic and mechanical behaviours. In this paper, we analyse the fracture behaviour by considering the competition of electromagnetic and mechanical behaviours. In order to study the central crack problem of a superconducting strip with different thicknesses, we replace the electromagnetic body force with the total surface force. Using a Fourier transform method, the boundary value problem is reduced to a singular integral equation. By solving the singular integral equation, we obtain the stress intensity factors for two different crack lengths during field descent. The results show that the stress intensity factor is not a monotonic function of the thickness and that two competing factors dominate in different field regions. It is necessary to obtain the optimized thickness by considering both the superconductivity and mechanical behaviour in the superconducting strip.

  15. Qualification of niobium materials for superconducting radio frequency cavity applications: View of a condensed matter physicist

    SciTech Connect

    Roy, S. B.; Myneni, G. R.

    2015-12-04

    We address the issue of qualifications of the niobium materials to be used for superconducting radio frequency (SCRF) cavity fabrications, from the point of view of a condensed matter physicist/materials scientist. We focus on the particular materials properties of niobium required for the functioning a SCRF cavity, and how to optimize the same properties for the best SCRF cavity performance in a reproducible manner. In this way the niobium materials will not necessarily be characterized by their purity alone, but in terms of those materials properties, which will define the limit of the SCRF cavity performance and also other related material properties, which will help to sustain this best SCRF cavity performance. Furthermore we point out the need of standardization of the post fabrication processing of the niobium-SCRF cavities, which does not impair the optimized superconducting and thermal properties of the starting niobium-materials required for the reproducible performance of the SCRF cavities according to the design values.

  16. Method for etching thin films of niboium and niobium-containing compounds for preparing superconductive circuits

    DOEpatents

    Kampwirth, R.T.; Schuller, I.K.; Falco, C.M.

    1979-11-23

    An improved method of preparing thin film superconducting electrical circuits of niobium or niobium compounds is provided in which a thin film of the niobium or niobium compound is applied to a nonconductive substrate and covered with a layer of photosensitive material. The sensitive material is in turn covered with a circuit pattern exposed and developed to form a mask of the circuit in photoresistive material on the surface of the film. The unmasked excess niobium film is removed by contacting the substrate with an aqueous etching solution of nitric acid, sulfuric acid, and hydrogen fluoride, which will rapidly etch the niobium compound without undercutting the photoresist. A modification of the etching solution will permit thin films to be lifted from the substrate without further etching.

  17. First-principles calculations of niobium hydride formation in superconducting radio-frequency cavities

    SciTech Connect

    Ford, Denise C.; Cooley, Lance D.; Seidman, David N.

    2013-09-01

    Niobium hydride is suspected to be a major contributor to degradation of the quality factor of niobium superconducting radio-frequency (SRF) cavities. In this study, we connect the fundamental properties of hydrogen in niobium to SRF cavity performance and processing. We modeled several of the niobium hydride phases relevant to SRF cavities and present their thermodynamic, electronic, and geometric properties determined from calculations based on density-functional theory. We find that the absorption of hydrogen from the gas phase into niobium is exothermic and hydrogen becomes somewhat anionic. The absorption of hydrogen by niobium lattice vacancies is strongly preferred over absorption into interstitial sites. A single vacancy can accommodate six hydrogen atoms in the symmetrically equivalent lowest-energy sites and additional hydrogen in the nearby interstitial sites affected by the strain field: this indicates that a vacancy can serve as a nucleation center for hydride phase formation. Small hydride precipitates may then occur near lattice vacancies upon cooling. Vacancy clusters and extended defects should also be enriched in hydrogen, potentially resulting in extended hydride phase regions upon cooling. We also assess the phase changes in the niobium-hydrogen system based on charge transfer between niobium and hydrogen, the strain field associated with interstitial hydrogen, and the geometry of the hydride phases. The results of this study stress the importance of not only the hydrogen content in niobium, but also the recovery state of niobium for the performance of SRF cavities.

  18. Superconducting Niobium-Titanium: Enabler for Affordable MRI and the Search for the Higgs Boson

    NASA Astrophysics Data System (ADS)

    Berlincourt, T. G.

    2016-01-01

    In 1961, Bell Telephone Laboratories researchers startled the world of physics by reporting that, at temperatures near absolute zero, a superconducting niobium-tin compound could support enormous electric current densities without resistance in the presence of very high magnetic fields. Suddenly, it became possible to fabricate supermagnets that generate high magnetic fields with unprecedented efficiency and economy. Scientists raced to find additional such materials and also to account theoretically for their behavior. Disregarded early on as unpromising, niobium-titanium alloys eventually emerged from among thousands of superconductors to become the most widely used, finding application in many thousands of MRI medical imaging systems and in huge particle accelerator magnets. In 1962, at Atomics International, experiments that revealed the supermagnet promise of niobium-titanium alloys also made essential contributions to the confirmation of the initially overlooked superconductivity theories of Soviet scientists Ginzburg, Landau, Abrikosov, and Gor'kov as the appropriate framework for understanding the physics of high magnetic field superconductivity.

  19. A study on the effect of tantalum-impurity content on the superconducting properties of niobium materials used for making superconducting radio frequency cavities

    SciTech Connect

    S B Roy, L S Sharath Chandra, M K Chattopadhyay, M K Tiwari, G S Lodha, G R Myneni

    2012-10-01

    Niobium materials in highly pure form are used in the fabrication of superconducting radio frequency cavities. We present here a study of the superconducting properties of such niobium materials that have been used in the fabrication of high accelerating gradient superconducting radio frequency cavities after determining their tantalum-impurity contents using a synchrotron-based x-ray fluorescence spectroscopy technique. Our results show that there is a small change in superconducting parameters such as T{sub C},H{sub C1} and H{sub C2} when the tantalum-impurity content varies from ≈150 to ≈1300 ppm. In contrast, a buffered chemical polishing of the same niobium samples changes all these superconducting parameters more significantly. The implications of these results on the performance of niobium superconducting radio frequency cavities are discussed.

  20. Reclamation of niobium compounds from ionic liquid electrochemical polishing of superconducting radio frequency cavities

    SciTech Connect

    Wixtrom, Alex I.; Buhler, Jessica E.; Reece, Charles E.; Abdel-Fattah, Tarek M.

    2013-06-01

    Recent research has shown that choline chloride (vitamin B4)-based solutions can be used as a greener alternative to acid-based electrochemical polishing solutions. This study demonstrated a successful method for electrochemical deposition of niobium compounds onto the surface of copper substrates using a novel choline chloride-based ionic liquid. Niobium ions present in the ionic liquid solution were dissolved into the solution prior to deposition via electrochemical polishing of solid niobium. A black coating was clearly visible on the surface of the Cu following deposition. This coating was analyzed using scanning electron microscopy (SEM), electron dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and X-ray fluorescence spectroscopy (XRF). This ionic liquid-based electrochemical deposition method effectively recycles previously dissolved niobium from electrochemical polishing of superconducting radio frequency (SRF) cavities.

  1. An evolutionary yield function based on Barlat 2000 yield function for the superconducting niobium sheet

    SciTech Connect

    Darbandi, Payam; Pourboghrat, Farhang

    2011-08-22

    Superconducting radio frequency (SRF) niobium cavities are widely used in high-energy physics to accelerate particle beams in particle accelerators. The performance of SRF cavities is affected by the microstructure and purity of the niobium sheet, surface quality, geometry, etc. Following optimum strain paths in the forming of these cavities can significantly control these parameters. To select these strain paths, however, information about the mechanical behavior, microstructure, and formability of the niobium sheet is required. In this study the Barlat 2000 yield function has been used as a yield function for high purity niobium. Results from this study showed that, due to intrinsic behavior, it is necessary to evolve the anisotropic coefficients of Barlat's yield function in order to properly model the plastic behavior of the niobium sheet. The accuracy of the newly developed evolutionary yield function was verified by applying it to the modeling of the hydrostatic bulging of the niobium sheet. Also, in a separate attempt crystal plasticity finite element method was use to model the behavior of the polycrystalline niobium sheet with a particular initial texture.

  2. Laser nitriding for niobium superconducting radio-frequency accelerator cavities

    SciTech Connect

    Senthilraja Singaravelu, John Klopf, Gwyn Williams, Michael Kelley

    2010-10-01

    Particle accelerators are a key tool for scientific research ranging from fundamental studies of matter to analytical studies at light sources. Cost-forperformance is critical, both in terms of initial capital outlay and ongoing operating expense, especially for electricity. It depends on the niobium superconducting radiofrequency (SRF) accelerator cavities at the heart of most of these machines. Presently Nb SRF cavities operate near 1.9 K, well (and expensively) below the 4.2 K atmospheric boiling point of liquid He. Transforming the 40 nm thick active interior surface layer from Nb to delta NbN (Tc = 17 K instead of 9.2 K) appears to be a promising approach. Traditional furnace nitriding appears to have not been successful for this. Further, exposing a complete SRF cavity to the time-temperature history required for nitriding risks mechanical distortion. Gas laser nitriding instead has been applied successfully to other metals [P.Schaaf, Prog. Mat. Sci. 47 (2002) 1]. The beam dimensions and thermal diffusion length permit modeling in one dimension to predict the time course of the surface temperature for a range of per-pulse energy densities. As with the earlier work, we chose conditions just sufficient for boiling as a reference point. We used a Spectra Physics HIPPO nanosecond laser (l = 1064 nm, Emax= 0.392 mJ, beam spot@ 34 microns, PRF =15 – 30 kHz) to obtain an incident fluence of 1.73 - 2.15 J/cm2 for each laser pulse at the target. The target was a 50 mm diameter SRF-grade Nb disk maintained in a nitrogen atmosphere at a pressure of 550 – 625 torr and rotated at a constant speed of 9 rpm. The materials were examined by scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and x-ray diffraction (XRD). The SEM images show a sharp transition with fluence from a smooth, undulating topography to significant roughening, interpreted here as the onset of ablation. EPMA measurements of N/Nb atom ratio as a function of depth found a constant

  3. Improvement and protection of niobium surface superconductivity by atomic layer deposition and heat treatment

    SciTech Connect

    Proslier, T.; Zasadzinski, J.; Moore, J.; Pellin, M.; Elam, J.; Cooley, L.; Antoine, C.; /Saclay

    2008-11-01

    A method to treat the surface of Nb is described, which potentially can improve the performance of superconducting rf cavities. We present tunneling and x-ray photoemission spectroscopy measurements at the surface of cavity-grade niobium samples coated with a 3 nm alumina overlayer deposited by atomic layer deposition. The coated samples baked in ultrahigh vacuum at low temperature degraded superconducting surface. However, at temperatures above 450 C, the tunneling conductance curves show significant improvements in the superconducting density of states compared with untreated surfaces.

  4. Electrical modulation of superconducting critical temperature in liquid-gated thin niobium films

    SciTech Connect

    Choi, Jiman; Pradheesh, R.; Chong, Yonuk Chae, Dong-Hun; Kim, Hyungsang; Im, Hyunsik

    2014-07-07

    We demonstrate that the superconducting critical temperature (T{sub c}) of thin niobium films can be electrically modulated in a liquid-gated geometry device. T{sub c} can be suppressed and enhanced by applying positive and negative gate voltage, respectively, in a reversible manner within a range of about 0.1 K. At a fixed temperature below T{sub c}, we observed that the superconducting critical current can be modulated by gate voltage. This result suggests a possibility of an electrically controlled switching device operating at or above liquid helium temperature, where superconductivity can be turned on or off solely by the applied gate voltage.

  5. Review of ingot niobium as a material for superconducting radiofrequency accelerating cavities

    SciTech Connect

    Kneisel, P.; Ciovati, G.; Dhakal, P.; Saito, K.; Singer, W.; Singer, X.; Myneni, G. R.

    2014-12-01

    As a result of collaboration between Jefferson Lab and niobium manufacturer Companhia Brasileira de Metalurgia e Mineração (CBMM), ingot niobium was explored as a possible material for superconducting radiofrequency (SRF) cavity fabrication. The first single cell cavity from large-grain high purity niobium was fabricated and successfully tested at Jefferson Lab in 2004. This work triggered research activities in other SRF laboratories around the world. The large-grain (LG) niobium became not only an interesting alternative material for cavity builders, but also material scientists and surface scientists were eager to participate in the development of this technology. Many single cell cavities made from material of different suppliers have been tested successfully and several multi-cell cavities have shown performances comparable to the best cavities made from standard fine-grain niobium. Several 9-cell cavities fabricated by Research Instruments and tested at DESY exceeded the best performing fine grain cavities with a record accelerating gradient of Eacc=45.6 MV/m. The quality factor of those cavities was also higher than that of fine-grain (FG) cavities processed with the same methods. Such performance levels push the state-of-the art of SRF technology and are of great interest for future accelerators. This contribution reviews the development of ingot niobium technology and highlights some of the differences compared to standard FG material and opportunities for further developments.

  6. Review of ingot niobium as a material for superconducting radiofrequency accelerating cavities

    DOE PAGESBeta

    Kneisel, P.; Ciovati, G.; Dhakal, P.; Saito, K.; Singer, W.; Singer, X.; Myneni, G. R.

    2014-12-01

    As a result of collaboration between Jefferson Lab and niobium manufacturer Companhia Brasileira de Metalurgia e Mineração (CBMM), ingot niobium was explored as a possible material for superconducting radiofrequency (SRF) cavity fabrication. The first single cell cavity from large-grain high purity niobium was fabricated and successfully tested at Jefferson Lab in 2004. This work triggered research activities in other SRF laboratories around the world. The large-grain (LG) niobium became not only an interesting alternative material for cavity builders, but also material scientists and surface scientists were eager to participate in the development of this technology. Many single cell cavities mademore » from material of different suppliers have been tested successfully and several multi-cell cavities have shown performances comparable to the best cavities made from standard fine-grain niobium. Several 9-cell cavities fabricated by Research Instruments and tested at DESY exceeded the best performing fine grain cavities with a record accelerating gradient of Eacc=45.6 MV/m. The quality factor of those cavities was also higher than that of fine-grain (FG) cavities processed with the same methods. Such performance levels push the state-of-the art of SRF technology and are of great interest for future accelerators. This contribution reviews the development of ingot niobium technology and highlights some of the differences compared to standard FG material and opportunities for further developments.« less

  7. Review of ingot niobium as a material for superconducting radiofrequency accelerating cavities

    NASA Astrophysics Data System (ADS)

    Kneisel, P.; Ciovati, G.; Dhakal, P.; Saito, K.; Singer, W.; Singer, X.; Myneni, G. R.

    2015-02-01

    As a result of collaboration between Jefferson Lab and niobium manufacturer Companhia Brasileira de Metalurgia e Mineração (CBMM), ingot niobium was explored as a possible material for superconducting radiofrequency (SRF) cavity fabrication. The first single cell cavity from large-grain high purity niobium was fabricated and successfully tested at Jefferson Lab in 2004. This work triggered research activities in other SRF laboratories around the world. Large-grain (LG) niobium became not only an interesting alternative material for cavity builders, but also material scientists and surface scientists were eager to participate in the development of this technology. Many single cell cavities made from material of different suppliers have been tested successfully and several multi-cell cavities have shown performances comparable to the best cavities made from standard fine-grain niobium. Several 9-cell cavities fabricated by Research Instruments and tested at DESY exceeded the best performing fine grain cavities with a record accelerating gradient of Eacc=45.6 MV/m. The quality factor of those cavities was also higher than that of fine-grain (FG) cavities processed with the same methods. Such performance levels push the state-of-the art of SRF technology and are of great interest for future accelerators. This contribution reviews the development of ingot niobium technology and highlights some of the differences compared to standard FG material and opportunities for further developments.

  8. Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

    SciTech Connect

    Romanenko, A.; Grassellino, A.

    2013-06-24

    Utilizing difference in temperature dependencies we decoupled Bardeen-Cooper-Schrieffer (BCS) and residual components of the microwave surface resistance of superconducting niobium at all rf fields up to B{sub rf}{approx}115 mT. We reveal that the residual resistance decreases with field at B{sub rf} Less-Than-Or-Equivalent-To 40 mT and strongly increases in chemically treated niobium at B{sub rf}>80 mT. We find that BCS surface resistance is weakly dependent on field in the clean limit, whereas a strong and peculiar field dependence emerges after 120 Degree-Sign C vacuum baking.

  9. Development of niobium spoke cavities for a superconducting light-ion Linac.

    SciTech Connect

    Shepard, K. W.

    1998-11-18

    This paper reports the development of 350 MHz niobium superconducting cavities for the velocity range 0.2< v/c <0.6. Such cavities could be used to form a linac of exceptional flexibility, capable of efficiently accelerating beams of either protons, deuterons, or any of a wide range of light ions, at intensities sufficient for a production beam for a radioactive beam facility. Results of numerical modeling for several resonator geometries are presented. The design and construction status of prototype niobium cavities is discussed.

  10. Structure, texture, and properties of superconductive electrolytic niobium coatings on nickel and copper substrates

    NASA Astrophysics Data System (ADS)

    Kolosov, V. N.; Shevyrev, A. A.

    2015-05-01

    Structure, texture, chemical purity, and other characteristics of superconductive niobium coatings prepared via electrochemical deposition onto nickel and copper substrates in (LiF + NaF + KF)eut + 5 wt % K2NbF7 molten salt are studied. It is shown that, when depositing the coatings onto nickel, the intermediate layer of Ni3Nb and NiNb intermetallides is formed at the substrate-coating interface, which inhibits the diffusion of nickel in niobium. The nickel concentration in niobium coatings above this layer is (2-7) × 10-2 wt %. In coatings deposited onto the copper substrate the copper content does not exceed 1.5 × 10-4 wt %, and from the viewpoint of the amount of impurities, niobium is considered as a high purity metal. The dynamics of structure modifications in niobium coatings and changes in microdeformations and dislocation density in the deposited metal are explored depending on the current density at the cathode.

  11. Surface analyses of electropolished niobium samples for superconducting radio frequency cavity

    SciTech Connect

    Tyagi, P. V.; Nishiwaki, M.; Saeki, T.; Sawabe, M.; Hayano, H.; Noguchi, T.; Kato, S.

    2010-07-15

    The performance of superconducting radio frequency niobium cavities is sometimes limited by contaminations present on the cavity surface. In the recent years extensive research has been done to enhance the cavity performance by applying improved surface treatments such as mechanical grinding, electropolishing (EP), chemical polishing, tumbling, etc., followed by various rinsing methods such as ultrasonic pure water rinse, alcoholic rinse, high pressure water rinse, hydrogen per oxide rinse, etc. Although good cavity performance has been obtained lately by various post-EP cleaning methods, the detailed nature about the surface contaminants is still not fully characterized. Further efforts in this area are desired. Prior x-ray photoelectron spectroscopy (XPS) analyses of EPed niobium samples treated with fresh EP acid, demonstrated that the surfaces were covered mainly with the niobium oxide (Nb{sub 2}O{sub 5}) along with carbon, in addition a small quantity of sulfur and fluorine were also found in secondary ion mass spectroscopy (SIMS) analysis. In this article, the authors present the analyses of surface contaminations for a series of EPed niobium samples located at various positions of a single cell niobium cavity followed by ultrapure water rinsing as well as our endeavor to understand the aging effect of EP acid solution in terms of contaminations presence at the inner surface of the cavity with the help of surface analytical tools such as XPS, SIMS, and scanning electron microscope at KEK.

  12. Modifications of Superconducting Properties of Niobium Caused by Nitrogen Doping Recipes for High Q Cavities

    SciTech Connect

    Vostrikov, Alexander; Checchin, Mattia; Grassellino, Anna; Kim, Young-Kee; Romanenko, Alexander

    2015-06-01

    A study is presented on the superconducting properties of niobium used for the fabrication of the SRF cavities after treating by recently discovered nitrogen doping methods. Cylindrical niobium samples have been subjected to the standard surface treatments applied to the cavities (electro-polishing, l 20°C bake) and compared with samples treated by additional nitrogen doping recipes routinely used to reach ultra-high quality factor values (>3· 1010 at 2 K, 16 MV/m). The DC magnetization curves and the complex magnetic AC susceptibility have been measured. Evidence for the lowered field of first flux penetration after nitrogen doping is found suggesting a correlation with the lowered quench fields. Superconducting critical temperatures Tc = 9.25 K are found to be in agreement with previous measurements, and no strong effect on the critical surface field (Bd) from nitrogen doping was found.

  13. Simulation of nonlinear superconducting rf losses derived from characteristic topography of etched and electropolished niobium surfaces

    NASA Astrophysics Data System (ADS)

    Xu, Chen; Reece, Charles E.; Kelley, Michael J.

    2016-03-01

    A simplified numerical model has been developed to simulate nonlinear superconducting radiofrequency (SRF) losses on Nb surfaces. This study focuses exclusively on excessive surface resistance (Rs ) losses due to the microscopic topographical magnetic field enhancements. When the enhanced local surface magnetic field exceeds the superconducting critical transition magnetic field Hc , small volumes of surface material may become normal conducting and increase the effective surface resistance without inducing a quench. We seek to build an improved quantitative characterization of this qualitative model. Using topographic data from typical buffered chemical polish (BCP)- and electropolish (EP)-treated fine grain niobium, we have estimated the resulting field-dependent losses and extrapolated this model to the implications for cavity performance. The model predictions correspond well to the characteristic BCP versus EP high field Q0 performance differences for fine grain niobium. We describe the algorithm of the model, its limitations, and the effects of this nonlinear loss contribution on SRF cavity performance.

  14. Structure, texture, and properties of superconductive electrolytic niobium coatings on glassy carbon

    NASA Astrophysics Data System (ADS)

    Kolosov, V. N.; Shevyrev, A. A.

    2016-01-01

    Superconductive electrolytic niobium coatings 0.1-100 μm thick are prepared via electrochemical deposition onto SU-2000 glassy carbon substrates in (LiF + NaF + KF)eut-K2NbF7 molten salt. Their structure, texture, and residual stresses are investigated by X-ray diffraction methods. It is shown that, when depositing the coatings, the diffusion superconductive layer of niobium carbide is formed at the substrate-coating interface. The sequence of changes in the axis of the texture of niobium coating from <100> through <211> to a textureless state with an increase in their thickness is established. It is found that, in the interval 0.5-5 μm, the sign of the stress changes (compressive stresses change into tensile stresses) and it reaches its maximum value. With an increase in the coating thickness from 5 to 100 μm, tensile stresses decrease from 345 to 80 MPa. It is shown that the coatings formed can be used as the material for creating a working layer of a superconducting cryogenic gyroscope rotor.

  15. 2D barrier in a superconducting niobium square

    SciTech Connect

    Joya, Miryam R. Barba-ortega, J.; Sardella, Edson

    2014-11-05

    The presence of barriers changes the vortex structure in superconducting Nb square in presence of a uniform applied magnetic field. The Cooper pair configurations in a mesoscopics superconducting square of Nb with a barrier are calculated within the nonlinear Ginzburg Landau equations. We predict the nucleation of multi-vortex states into the sample and a soft entry of the magnetic field inside and around into the barrier. A novel and non-conventional vortex configurations occurs at determined magnetic field.

  16. Persistence of superconductivity in niobium ultrathin films grown on R-plane sapphire

    NASA Astrophysics Data System (ADS)

    Delacour, Cécile; Ortega, Luc; Faucher, Marc; Crozes, Thierry; Fournier, Thierry; Pannetier, Bernard; Bouchiat, Vincent

    2011-04-01

    We report on a combined structural and electronic analysis of niobium ultrathin films (from 2 to 10 nm) deposited in ultrahigh vacuum on atomically flat R-plane sapphire wafers. A textured polycrystalline morphology is observed for the thinnest films, showing that heteroepitaxy is not achieved under a thickness of 3.3 nm, which almost coincides with the first measurement of a superconducting state. The superconducting critical temperature rise takes place on a very narrow thickness range, of the order of a single monolayer (ML). The thinnest superconducting sample (3 nm/9 ML) has an offset critical temperature above 4.2 K and can be processed by standard nanofabrication techniques to generate air- and time-stable superconducting nanostructures, useful for quantum devices.

  17. Method of manufacturing a niobium-aluminum-germanium superconductive material

    DOEpatents

    Wang, J.L.F.; Pickus, M.R.; Douglas, K.E.

    A method for manufacturing flexible Nb/sub 3/ (Al,Ge) multifilamentary superconductive material in which a sintered porous Nb compact is infiltrated with an Al-Ge alloy. It is deformed and heat treated in a series of steps at successively higher temperatures preferably below 1000/sup 0/C during the heat treatment, cladding material such as copper can be applied to facilitate a deformation step preceding the heat treatment and can remain in place through the heat treatment to serve as a temperature stabilizer for the superconductive material produced. These lower heat treatment temperatures favor formation of filaments with reduced grain size and with more grain boundaries which in turn increase the current-carrying capacity of the superconductive material.

  18. Physical Properties of Niobium and Specifications for Fabrication of Superconducting Cavities

    SciTech Connect

    Antoine, C.; Foley, M.; Dhanaraj, N.; /Fermilab

    2011-07-01

    It is important to distinguish among the properties of niobium, the ones that are related to the cavity's SRF performances, the formability of the material, and the mechanical behavior of the formed cavity. In general, the properties that dictate each of the above mentioned characteristics have a detrimental effect on one another and in order to preserve the superconducting properties without subduing the mechanical behavior, a balance has to be established. Depending on the applications, some parameters become less important and an understanding of the physical origin of the requirements might help in this optimization. SRF applications require high purity niobium (high RRR), but pure niobium is very soft from fabrication viewpoint. Moreover conventional fabrication techniques tend to override the effects of any metallurgical process meant to strengthen it. As those treatments dramatically affect the forming of the material they should be avoided. These unfavorable mechanical properties have to be accounted for in the design of the cavities rather than in the material specification. The aim of this paper is to review the significance of the important mechanical properties used to characterize niobium and to present the optimal range of values. Most of the following information deals with the specification of sheets for cell forming unless otherwise noted.

  19. Progress on the Development of a Superconducting Connection for Niobium Cavities

    SciTech Connect

    Peter Kneisel, Gianluigi Ciovati, Jacek Sekutowicz ,Larry Turlington

    2009-06-01

    The availability of a superconducting connection between adjacent niobium radio-frequency (RF) cavities with the capability to carry up to 30 mT of the magnetic flux would be particularly of great benefit to layouts of long accelerators like the International Linear Collider (ILC). It would shorten the distances between structures and therefore the total length of an accelerator with the associated cost reductions. In addition, the superconducting connection would be ideal for a superstructure – two multi-cell cavities connected through a half wavelength long beam pipe providing the coupling. Two single-cell niobium cavities have been designed with Nb-1Zr flanges welded to one of the irises to allow a connection between them with a niobium gasket. A transition to the normal-conducting state of the connection due to the applied RF field causes a reduction of the cavities’ quality factor. The cavity design will be presented in this contribution along with possible choices of materials for the joint.

  20. Plasma etching of superconducting Niobium tips for scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Roychowdhury, A.; Dana, R.; Dreyer, M.; Anderson, J. R.; Lobb, C. J.; Wellstood, F. C.

    2014-07-01

    We have developed a reproducible technique for the fabrication of sharp superconducting Nb tips for scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. Sections of Nb wire with 250 μm diameter are dry etched in an SF6 plasma in a Reactive Ion Etcher. The gas pressure, etching time, and applied power are chosen to control the ratio of isotropic to anisotropic etch rates and produce the desired tip shape. The resulting tips are atomically sharp, with radii of less than 100 nm, mechanically stable, and superconducting. They generate good STM images and spectroscopy on single crystal samples of Au(111), Au(100), and Nb(100), as well as a doped topological insulator Bi2Se3 at temperatures ranging from 30 mK to 9 K.

  1. Plasma etching of superconducting Niobium tips for scanning tunneling microscopy

    SciTech Connect

    Roychowdhury, A.; Dana, R.; Dreyer, M.; Anderson, J. R.; Lobb, C. J.; Wellstood, F. C.

    2014-07-07

    We have developed a reproducible technique for the fabrication of sharp superconducting Nb tips for scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. Sections of Nb wire with 250 μm diameter are dry etched in an SF₆ plasma in a Reactive Ion Etcher. The gas pressure, etching time, and applied power are chosen to control the ratio of isotropic to anisotropic etch rates and produce the desired tip shape. The resulting tips are atomically sharp, with radii of less than 100 nm, mechanically stable, and superconducting. They generate good STM images and spectroscopy on single crystal samples of Au(111), Au(100), and Nb(100), as well as a doped topological insulator Bi₂Se₃ at temperatures ranging from 30 mK to 9 K.

  2. Laser polishing of niobium for application to superconducting radio frequency cavities

    SciTech Connect

    Singaravelu, Senthil; Klopf, John Michael; Xu, Chen; Krafft, Geoffrey; Kelley, Michael J.

    2012-09-01

    Superconducting radio frequency niobium cavities are at the heart of an increasing number of particle accelerators. Their performance is dominated by a several nanometer thick layer at the interior surface. Maximizing the smoothness of this surface is critical, and aggressive chemical treatments are now employed to this end. The authors describe laser-induced surface melting as an alternative 'greener' approach. Selection of laser parameters guided by modeling achieved melting that reduced the surface roughness from the fabrication process. The resulting topography was examined by scanning electron microscope and atomic force microscope (AFM). Plots of power spectral density computed from the AFM data give further insight into the effect of laser melting on the topography of the mechanically polished (only) niobium.

  3. Analysis of the medium field Q-slope in superconducting cavities made of bulk niobium

    SciTech Connect

    Gianluigi Ciovati; J. Halbritter

    2005-07-10

    The quality factor of superconducting radio-frequency cavities made of high purity, bulk niobium increases with rf field in the medium field range (peak surface magnetic field between 20 and about 100 mT). The causes for this effect are not clear yet. The dependence of the surface resistance on the peak surface magnetic field is typically linear and quadratic. This contribution will present an analysis of the medium field Q-slope data measured on cavities treated with buffered chemical polishing (BCP) at Jefferson Lab, as function of different treatments such as post-purification and low-temperature baking. The data have been compared with a model involving a combination of heating and of hysteresis losses due to ''strong-links'' formed or weakened at niobium surfaces during oxidation, which correlate to {delta}{Delta}/kT{sub c} changes by baking.

  4. Density and elasticity of superconducting niobium nitride under high pressure

    NASA Astrophysics Data System (ADS)

    Zou, Y.; Li, B.; Wang, X.; Chen, T.

    2013-12-01

    Hard superconducting materials are of considerable interest for specific electronic applications. Transition-metal (TM) nitrides have increasingly attracted attention because of their outstanding mechanical, optoelectronic, thermal, magnetic and/or superconducting properties and potential usage in a variety of technological areas, such as NbN exploited in superconducting and high hardness coatings. Previous hardness measurements on NbN by Vickers indentation method reported a Vickers hardness about 20 GPa and its bulk modulus was found close to that of cubic boron nitride. In addition, experimental studies and first-principles calculations have investigated the equation-of-state (EOS) for B1 structured NbN and provided important insights into the origin of its outstanding mechanical properties. In spite of its importance, to date, the high-pressure behavior and elastic properties of NbN are not well studied experimentally, in particular for the shear properties under pressure. In this study, we hot-pressed high quality (well-sintered, free of cracks, small grain size and homogeneous) polycrystalline NbN specimens and performed simultaneous measurements of compressional and shear wave travel times using ultrasonic interferometry techniques up to ~12 GPa at room temperature in a large-volume high-pressure apparatus. By fitting these experimental data to finite strain equations, the compressional and shear wave velocities, density, and the bulk and shear moduli as a function of pressure are all obtained. These new data not only allow us to compare with previous EOS data on NbN and those of other transition metal nitrides, but also enable us to further explore the constitutive relations between elastic moduli and hardness in these nitrides.

  5. Effect of low temperature baking on the RF properties of niobium superconducting cavities for particle accelerators

    SciTech Connect

    Gianluigi Ciovati

    2004-03-01

    Radio-frequency superconducting (SRF) cavities are widely used to accelerate a charged particle beam in particle accelerators. The performance of SRF cavities made of bulk niobium has significantly improved over the last ten years and is approaching the theoretical limit for niobium. Nevertheless, RF tests of niobium cavities are still showing some ''anomalous'' losses that require a better understanding in order to reliably obtain better performance. These losses are characterized by a marked dependence of the surface resistance on the surface electromagnetic field and can be detected by measuring the quality factor of the resonator as a function of the peak surface field. A low temperature (100 C-150 C) ''in situ'' bake under ultra-high vacuum has been successfully applied as final preparation of niobium RF cavities by several laboratories over the last few years. The benefits reported consist mainly of an improvement of the cavity quality factor at low field and a recovery from ''anomalous'' losses (so-called ''Q-drop'') without field emission at higher field. A series of experiments with a CEBAF single-cell cavity have been carried out at Jefferson Lab to carefully investigate the effect of baking at progressively higher temperatures for a fixed time on all the relevant material parameters. Measurements of the cavity quality factor in the temperature range 1.37 K-280 K and resonant frequency shift between 6 K-9.3 K provide information about the surface resistance, energy gap, penetration depth and mean free path. The experimental data have been analyzed with the complete BCS theory of superconductivity. The hydrogen content of small niobium samples inserted in the cavity during its surface preparation was analyzed with Nuclear Reaction Analysis (NRA). The single-cell cavity has been tested at three different temperatures before and after baking to gain some insight on thermal conductivity and Kapitza resistance and the data are compared with different models

  6. Morphology of the Superconducting Vortex Lattice in Ultrapure Niobium

    NASA Astrophysics Data System (ADS)

    Mühlbauer, S.; Pfleiderer, C.; Böni, P.; Laver, M.; Forgan, E. M.; Fort, D.; Keiderling, U.; Behr, G.

    2009-04-01

    The morphology of the superconducting flux line lattice (FLL) of Nb comprises gradual variations with various lock-in transitions and symmetry breaking rotations. We report a comprehensive small-angle neutron scattering study of the FLL in an ultrapure single crystal of Nb as a function of the orientation of the applied magnetic field. We attribute the general morphology of the FLL and its orientation to three dominant mechanisms; first, nonlocal contributions, second, the transition between open and closed Fermi surface sheets and, third, the intermediate mixed state between the Meissner and the Shubnikov phase.

  7. Surface polishing of niobium for superconducting radio frequency (SRF) cavity applications

    SciTech Connect

    Zhao, Liang

    2014-08-01

    Niobium cavities are important components in modern particle accelerators based on superconducting radio frequency (SRF) technology. The interior of SRF cavities are cleaned and polished in order to produce high accelerating field and low power dissipation on the cavity wall. Current polishing methods, buffered chemical polishing (BCP) and electro-polishing (EP), have their advantages and limitations. We seek to improve current methods and explore laser polishing (LP) as a greener alternative of chemical methods. The topography and removal rate of BCP at different conditions (duration, temperature, sample orientation, flow rate) was studied with optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Differential etching on different crystal orientations is the main contributor to fine grain niobium BCP topography, with gas evolution playing a secondary role. The surface of single crystal and bi-crystal niobium is smooth even after heavy BCP. The topography of fine grain niobium depends on total removal. The removal rate increases with temperature and surface acid flow rate within the rage of 0~20 °C, with chemical reaction being the possible dominate rate control mechanism. Surface flow helps to regulate temperature and avoid gas accumulation on the surface. The effect of surface flow rate on niobium EP was studied with optical microscopy, atomic force microscopy (AFM), and power spectral density (PSD) analysis. Within the range of 0~3.7 cm/s, no significant difference was found on the removal rate and the macro roughness. Possible improvement on the micro roughness with increased surface flow rate was observed. The effect of fluence and pulse accumulation on niobium topography during LP was studied with optical microscopy, SEM, AFM, and PSD analysis. Polishing on micro scale was achieved within fluence range of 0.57~0.90 J/cm2, with pulse accumulation adjusted accordingly. Larger area treatment was proved possible by

  8. Laser Processing on the Surface of Niobium Superconducting Radio-Frequency Accelerator Cavities

    NASA Astrophysics Data System (ADS)

    Singaravelu, Senthilraja; Klopf, Michael; Krafft, Geoffrey; Kelley, Michael

    2011-03-01

    Superconducting Radio frequency (SRF) niobium cavities are at the heart of an increasing number of particle accelerators.~ Their performance is dominated by a several nm thick layer at the interior surface. ~Maximizing its smoothness is found to be critical and aggressive chemical treatments are employed to this end.~ We describe laser-induced surface melting as an alternative ``greener'' approach.~ Modeling guided selection of parameters for irradiation with a Q-switched Nd:YAG laser.~ The resulting topography was examined by SEM, AFM and Stylus Profilometry.

  9. Ferromagnetic artificial pinning centers in superconducting niobium-titanium wires

    NASA Astrophysics Data System (ADS)

    Rizzo, Nicholas David

    1997-09-01

    Ferromagnetic artificial pinning centers were used in superconducting NbTi wires to achieve a large critical current density (Jsb{c}) in a magnetic field. The wire processing was developed to make four wires that contained nanometer-sized arrays of Ni or Fe pins inside micron-sized filaments of a Nbsb{0.36}Tiosb{0.64} alloy. The optimum pin size and spacing for maximum Jsb{c} was approximately 5 nm and 30 nm, respectively. A ferromagnetic pin volume of only 2% Ni produced Jsb{c}'s (e.g., 2500 A/mmsp2 at 5 T, 4.2 K) that were comparable to those of other NbTi wires that have pin volumes ranging from 12% to 20%. Therefore, ferromagnetic artificial pins are more effective than nonmagnetic pins for a given volume percent. Saturation Magnetization measurements on the wires showed a correlation between an increase in the amount of Ni remaining ferromagnetic in the wires and an increase in Jsb{c}. These results suggest wires with larger volumes of Ni may have even higher Jsb{c}'s. The critical temperature (Tsb{c}) of the best wire with Ni pins was only slightly depressed (Tsb{c}≈8.6 K) from the measured bulk value for Nbsb{0.36}Tiosb{0.64} (Tsb{c}≈9 K), suggesting that proximity effects from the Ni are not severe. Wires with small superconducting filament diameters (0.3 mum) displayed enhanced Jsb{c} at low fields (B ≤ 5 T) that was attributed to pinning at the filament surfaces. Finally, for wires with large filaments, the optimum bulk pinning force (Fsb{p}) dependence on B was well described by the form Fsb{p}~ bsp{1/2}(1-b) where b = B/Hsb{c2} and Hsb{c2} is the upper critical field of the superconductor. This form is interpreted as a general result of the large optimum pin spacings in our APC wires. This thesis research was the result of a collaboration between Yale University and IGC-Advanced Superconductors (Waterbury, CT).

  10. Surface studies of niobium chemically polished under conditions for superconducting radiofrequency cavity production

    SciTech Connect

    Hui Tian; Michael Kelley; Charles Reece

    2005-11-14

    The performance of niobium superconducting radiofrequency accelerator cavities is strongly impacted by the topmost several nanometers of the active (interior) surface, especially by the final surface conditioning treatments. We examined the effect of the most commonly employed treatment, buffered chemical polishing (BCP), on polycrystalline niobium sheet over a range of realistic solution flow rates using electron back scatter diffraction (EBSD), stylus profilometry, atomic force microscopy, laboratory XPS and synchrotron (variable photon energy) XPS, seeking to collect statistically significant data sets. We found that the predominant general surface orientation is (100), but others are also present and at the atomic-level details of surface plane orientation are more complex. The post-etch surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of niobium pentoxide, whose thickness increases with solution flow rate to a maximum of 1.3 - 1.4 times that resulting from static solution. The standard deviation of the roughness measurements is ?? 30% and that of the surface composition is ?? 5%.

  11. Ga Lithography in Sputtered Niobium for Superconductive Micro and Nanowires.

    SciTech Connect

    Henry, Michael David; Lewis, Rupert M.; Wolfley, Steven L.; Monson, Todd C.

    2014-08-18

    This work demonstrates the use of FIB implanted Ga as a lithographic mask for plasma etching of Nb films. Using a highly collimated Ga beam of a FIB, Nb is implanted 12 nm deep with a 14 nm thick Ga layer providing etch selectivity better than 15:1 with fluorine based etch chemistry. Implanted square test patterns, both 10 um by and 10 um and 100 um by 100 um, demonstrate that doses above than 7.5 x 1015 cm-2 at 30 kV provide adequate mask protection for a 205 nm thick, sputtered Nb film. The resolution of this dry lithographic technique is demonstrated by fabrication of nanowires 75 nm wide by 10 um long connected to 50 um wide contact pads. The residual resistance ratio of patterned Nb films was 3. The superconducting transition temperature, Tc =7.7 K, was measured using MPMS. This nanoscale, dry lithographic technique was extended to sputtered TiN and Ta here and could be used on other fluorine etched superconductors such as NbN, NbSi, and NbTi.

  12. Ga Lithography in Sputtered Niobium for Superconductive Micro and Nanowires.

    DOE PAGESBeta

    Henry, Michael David; Lewis, Rupert M.; Wolfley, Steven L.; Monson, Todd C.

    2014-08-18

    This work demonstrates the use of FIB implanted Ga as a lithographic mask for plasma etching of Nb films. Using a highly collimated Ga beam of a FIB, Nb is implanted 12 nm deep with a 14 nm thick Ga layer providing etch selectivity better than 15:1 with fluorine based etch chemistry. Implanted square test patterns, both 10 um by and 10 um and 100 um by 100 um, demonstrate that doses above than 7.5 x 1015 cm-2 at 30 kV provide adequate mask protection for a 205 nm thick, sputtered Nb film. The resolution of this dry lithographic techniquemore » is demonstrated by fabrication of nanowires 75 nm wide by 10 um long connected to 50 um wide contact pads. The residual resistance ratio of patterned Nb films was 3. The superconducting transition temperature, Tc =7.7 K, was measured using MPMS. This nanoscale, dry lithographic technique was extended to sputtered TiN and Ta here and could be used on other fluorine etched superconductors such as NbN, NbSi, and NbTi.« less

  13. Ga lithography in sputtered niobium for superconductive micro and nanowires

    SciTech Connect

    Henry, M. David; Wolfley, Steve; Monson, Todd; Lewis, Rupert

    2014-08-18

    This work demonstrates the use of focused ion beam (FIB) implanted Ga as a lithographic mask for plasma etching of Nb films. Using a highly collimated Ga beam of a FIB, Nb is implanted 12 nm deep with a 14 nm thick Ga layer providing etch selectivity better than 15:1 with fluorine based etch chemistry. Implanted square test patterns, both 10 μm by 10 μm and 100 μm by 100 μm, demonstrate that doses above than 7.5 × 10{sup 15 }cm{sup −2} at 30 kV provide adequate mask protection for a 205 nm thick, sputtered Nb film. The resolution of this dry lithographic technique is demonstrated by fabrication of nanowires 75 nm wide by 10 μm long connected to 50 μm wide contact pads. The residual resistance ratio of patterned Nb films was 3. The superconducting transition temperature (T{sub c}) = 7.7 K was measured using a magnetic properties measurement system. This nanoscale, dry lithographic technique was extended to sputtered TiN and Ta here and could be used on other fluorine etched superconductors such as NbN, NbSi, and NbTi.

  14. The Preparation and Properties of Niobium Superconducting Structures Prepared by Electron Beam Evaporation in Uhv

    NASA Astrophysics Data System (ADS)

    Goodchild, Martin S.

    Available from UMI in association with The British Library. This work has achieved the development of a fabrication method for the realisation of superconductor-insulator -superconductor (SIS) junctions based on niobium thin films with an artificial barrier layer. Such devices are likely to have advantages over lead alloy devices because of the enhanced mechanical and chemical stability. A principal objective was to attempt to exploit the offset mask technology developed by Dolan that has been successfully employed by Davies et.al. in the realisation of lead alloy SIS junction heterodyne mixers. In order to transfer this technology to niobium based devices it is essential that an evaporation method is used to allow shadow formation beneath the offset mask. As a result of the chemical reactivity and the low vapour pressure of niobium, a UHV system has been developed which incorporates an electrostatically focussed electron beam evaporation source. This is capable of providing deposition rates of close to 10A/sec. with a source to substrate distance of 120mm. During deposition the system pressure is below 5 times 10 ^{-9} mbar. These process parameters have been recorded, for a number of depositions, on a specially built data acquisition system controlled by a BBC microcomputer. Such recording allows detailed comparison of conditions which helps in the understanding of differences between the superconducting behaviour of various films. A further extremely important aspect of these real time measurements is that it helps to ensure optimum settings of the focus conditions of the electron beam source. The results of the depositions are extremely encouraging with critical temperatures of between 9.1 and 9.3K being achieved. These results compare well with expected values for bulk niobium. An all-metal offset mask technology has been developed to replace the photo-resist technique pioneered by Dolan. This new method is needed because the photo-resist is not compatible

  15. Precise determination of the mass of a Cooper pair of electrons in superconducting niobium

    SciTech Connect

    Tate, J.

    1988-01-01

    A superconducting, thin-film niobium ring deposited on the equator of a precision quartz hemispherical rotor was used to measure the ratio of Planck's constant to the mass of a Cooper pair of electrons, h/m*. A precision of 5 ppm (statistical) and an accuracy of 30 ppm (systematic) were obtained for a combined, root sum of squares error of 30 ppm. As a result of two macroscopic quantum phenomena-flux quantization and the London moment, the flux through a rotating, superconducting ring is a multivalued function of its rotation frequency. The flux goes to zero at certain equally spaced frequencies. The ratio h/m* is proportional to this frequency spacing. It is also proportional to the cross sectional area of the niobium ring. Using the values for Planck's constant and the rest mass of the electron recommended in the most recent fundamental constants revision, the mass measured in this experiment is larger than twice the free electron mass by 84 +/- 30 ppm. The result disagrees with theoretical predictions that this experiment would observe a mass smaller than twice the free electron mass by 8 ppm.

  16. DEPOSITION OF NIOBIUM AND OTHER SUPERCONDUCTING MATERIALS WITH HIGH POWER IMPULSE MAGNETRON SPUTTERING: CONCEPT AND FIRST RESULTS

    SciTech Connect

    High Current Electronics Institute, Tomsk, Russia; Anders, Andre; Mendelsberg, Rueben J.; Lim, Sunnie; Mentink, Matthijs; Slack, Jonathan L.; Wallig, Joseph G.; Nollau, Alexander V.; Yushkov, Georgy Yu.

    2011-07-24

    Niobium coatings on copper cavities have been considered as a cost-efficient replacement of bulk niobium RF cavities, however, coatings made by magnetron sputtering have not quite lived up to high expectations due to Q-slope and other issues. High power impulse magnetron sputtering (HIPIMS) is a promising emerging coatings technology which combines magnetron sputtering with a pulsed power approach. The magnetron is turned into a metal plasma source by using very high peak power density of ~ 1 kW/cm{sup 2}. In this contribution, the cavity coatings concept with HIPIMS is explained. A system with two cylindrical, movable magnetrons was set up with custom magnetrons small enough to be inserted into 1.3 GHz cavities. Preliminary data on niobium HIPIMS plasma and the resulting coatings are presented. The HIPIMS approach has the potential to be extended to film systems beyond niobium, including other superconducting materials and/or multilayer systems.

  17. Superconducting and microstructural studies on sputtered niobium thin films for accelerating cavity applications

    NASA Astrophysics Data System (ADS)

    Bemporad, E.; Carassiti, F.; Sebastiani, M.; Lanza, G.; Palmieri, V.; Padamsee, H.

    2008-12-01

    The aim of the present research activity was to verify the influence of the applied bias voltage on the microstructural and functional properties of magnetron sputtering physical vapour deposition (MS-PVD) niobium thin films for use in superconducting resonant cavities for particle accelerators. Four different sets of samples were produced, by varying both the applied bias voltage and the nature of the substrate (copper or quartz). The morphological, microstructural, and mechanical properties of the coatings were experimentally determined by focused ion beam scanning electron microscopy (FIB-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and nanoindentation techniques, and then correlated to the applied bias and nature of the substrate. The superconducting properties (critical temperature Tc and residual resistivity) were determined by a calibrated four-contact probe and a cryogenic apparatus. The microstructures and surface properties of biased films grown on copper and quartz were compared. The observed differences are likely connected to the low conductivity of quartz that induces a re-sputtering effect and a consequent modification of the superconducting performances.

  18. Evidence of surface paramagnetism in niobium and consequences for the superconducting cavity surface impedance.

    SciTech Connect

    Prolier, T.; Kharitonov, M.; Pellin, M.; Zasadzinski, J.; Ciovati, G.

    2011-06-01

    The presence of magnetic impurities in native niobium oxides have been confirmed by Point contact spectroscopy (PCT), SQUID magnetometry and Electron paramagnetic resonance (EPR). All niobium (Nb) samples displayed a small impurity contribution to the magnetic susceptibility at low temperatures which exhibited Curie-Weiss behavior, indicative of weakly coupled localized paramagnetic moments. By examining Nb samples with widely varying surface-to-volume ratios (rods, foils, wires, powders) it was found that the impurity contribution is correlated with surface area. Tunneling measurements which use the native oxide layers as barriers exhibit a zero-bias conductance peak which splits in a magnetic field >; 4T, consistent with the Appelbaum-Anderson model for spin flip tunneling. Viewed together the experiments strongly suggest that the native oxides of Nb are intrinsically defective, and consistently exhibit localized paramagnetic moments caused by oxygen vacancies in Nb{sub 2}O{sub 5}. The computation of the surface impedance (R{sub s}) in presence of magnetic impurities in the Shiba approximation reveals the saturation at low temperature of R{sub s}, suggesting that magnetic impurities are responsible for the so-called residual resistance. These properties may have an impact on Nb based superconducting devices and shine a new light on the origin of the paramagnetic Meissner effect (PME).

  19. Design and performance of a new induction furnace for heat treatment of superconducting radiofrequency niobium cavities

    SciTech Connect

    Dhakal, Pashupati; Ciovati, Gianluigi; Myneni, Ganapati Rao; Rigby, Wayne; Wallace, John

    2012-06-15

    Superconducting radio frequency (SRF) cavities made of high purity niobium (Nb) are the building blocks of many modern particle accelerators. The fabrication process includes several cycles of chemical and heat treatment at low ({approx}120 Degree-Sign C) and high ({approx}800 Degree-Sign C) temperatures. In this contribution, we describe the design and performance of an ultra-high-vacuum furnace which uses an induction heating system to heat treat SRF cavities. Cavities are heated by radiation from the Nb susceptor. By using an all-niobium hot zone, contamination of the Nb cavity by foreign elements during heat treatment is minimized and allows avoiding subsequent chemical etching. The furnace was operated up to 1400 Degree-Sign C with a maximum pressure of {approx}1 Multiplication-Sign 10{sup -5} Torr and the maximum achievable temperature is estimated to be higher than 2000 Degree-Sign C. Initial results on the performance of a single cell 1.5 GHz cavity made of ingot Nb heat treated at 1200 Degree-Sign C using this new induction furnace and without subsequent chemical etching showed a reduction of the RF losses by a factor of {approx}2 compared to cavities made of fine-grain Nb which underwent standard chemical and heat treatments.

  20. Design and performance of a new induction furnace for heat treatment of superconducting radiofrequency niobium cavities

    SciTech Connect

    Pashupati Dhakal, Gianluigi Ciovati, Wayne Rigby, John Wallace, Ganapati Rao Myneni

    2012-06-01

    Superconducting radio frequency (SRF) cavities made of high purity niobium (Nb) are the building blocks of many modern particle accelerators. The fabrication process includes several cycles of chemical and heat treatment at low ({approx}120 deg C) and high ({approx}800 deg C) temperatures. In this contribution, we describe the design and performance of an ultra-high-vacuum furnace which uses an induction heating system to heat treat SRF cavities. Cavities are heated by radiation from the Nb susceptor. By using an all-niobium hot zone, contamination of the Nb cavity by foreign elements during heat treatment is minimized and allows avoiding subsequent chemical etching. The furnace was operated up to 1400 deg C with a maximum pressure of {approx}1 x 10{sup -5} Torr and the maximum achievable temperature is estimated to be higher than 2000 deg C. Initial results on the performance of a single cell 1.5 GHz cavity made of ingot Nb heat treated at 1200 deg C using this new induction furnace and without subsequent chemical etching showed a reduction of the RF losses by a factor of {approx}2 compared to cavities made of fine-grain Nb which underwent standard chemical and heat treatments.

  1. Laser polishing of niobium for superconducting radio-frequency accelerator applications

    SciTech Connect

    Zhao, Liang; Klopf, John M.; Reece, Charles E.; Kelley, Michael J.

    2014-08-01

    Interior surfaces of niobium cavities used in superconducting radio frequency accelerators are now obtained by buffered chemical polish and/or electropolish. Laser polishing is a potential alternative, having advantages of speed, freedom from noxious chemistry and availability of in-process inspection. We studied the influence of the laser power density and laser beam raster rate on the surface topography. These two factors need to be combined carefully to smooth the surface without damage. Computational modeling was used to estimate the surface temperature and gain insight into the mechanism of laser polishing. Power spectral density analysis of surface topography measurements shows that laser polishing can produce smooth topography similar to that obtained by electropolish. This is a necessary first step toward introducing laser polishing as an alternative to the currently practiced chemical polishing.

  2. Comparison of Deformation in High-Purity Single/Large Grain and Polycrystalline Niobium Superconducting Cavities

    SciTech Connect

    Ganapati Rao Myneni; Peter Kneisel

    2005-07-10

    The current approach for the fabrication of superconducting radio frequency (SRF) cavities is to roll and deep draw sheets of polycrystalline high-purity niobium. Recently, a new technique was developed at Jefferson Laboratory that enables the fabrication of single-crystal high-purity Nb SRF cavities. To better understand the differences between SRF cavities fabricated out of fine-grained polycrystalline sheet in the standard manner and single crystal cavities fabricated by the new technique, two half-cells were produced according to the two different procedures and compared using a variety of analytical techniques including optical microscopy, scanning laser confocal microscopy, profilometry, and X-ray diffraction. Crystallographic orientations, texture, and residual stresses were determined in the samples before and after forming and this poster presents the results of this ongoing study.

  3. Flux pinning characteristics in cylindrical ingot niobium used in superconducting radio frequency cavity fabrication

    SciTech Connect

    Dhavale Ashavai, Pashupati Dhakal, Anatolii A Polyanskii, Gianluigi Ciovati

    2012-04-01

    We present the results of from DC magnetization and penetration depth measurements of cylindrical bulk large-grain (LG) and fine-grain (FG) niobium samples used for the fabrication of superconducting radio frequency (SRF) cavities. The surface treatment consisted of electropolishing and low temperature baking as they are typically applied to SRF cavities. The magnetization data were fitted using a modified critical state model. The critical current density Jc and pinning force Fp are calculated from the magnetization data and their temperature dependence and field dependence are presented. The LG samples have lower critical current density and pinning force density compared to FG samples which implies a lower flux trapping efficiency. This effect may explain the lower values of residual resistance often observed in LG cavities than FG cavities.

  4. Recent RRR measurements on niobium for superconducting RF cavities at Fermilab

    SciTech Connect

    Bauer, P.; Boffo, C.; Hahn, E.; Hicks, D.; Foley, M.; McConologue, F.; Wokas, T.; /Fermilab

    2005-07-01

    Fermilab is developing superconducting RF cavities of the bulk Niobium (Nb) type. Several prototypes of a 3rd-harmonic cavity and a transverse deflecting mode (CKMtype) cavity were already built. The first three-cell third harmonic model recently achieved the expected performance limit [1]. The following reports on RRR measurements on samples cut from Nb sheets for the 3rd-harmonic and CKM prototype cavities. The RRR was measured upon receipt and after the chemical polishing and heat treatment steps used in the cavity fabrication. These measurements not only serve the purpose of quality control of the pre-cursor material but also as a check of the cavity processing. We also measured the RRR of the electron-beam welds using samples cut from plates produced by joining sheets by e-beam welding in the same device used for welding cavity parts. Finally we will discuss our next generation RRR measurement system, currently in the design stage.

  5. Method for determining hydrogen mobility as a function of temperature in superconducting niobium cavities

    DOEpatents

    May, Robert

    2008-03-11

    A method for determining the mobility of hydrogen as a function of temperature in superconducting niobium cavities comprising: 1) heating a cavity under test to remove free hydrogen; 2) introducing hydrogen-3 gas into the cavity; 3) cooling the cavity to allow absorption of hydrogen-3; and 4) measuring the amount of hydrogen-3 by: a) cooling the cavity to about 4.degree. K while flowing a known and regulated amount of inert carrier gas such as argon or helium into the cavity; b) allowing the cavity to warm at a stable rate from 4.degree. K to room temperature as it leaves the chamber; and c) directing the exit gas to an ion chamber radiation detector.

  6. Photoemission studies on BNL/AES/JLAB all niobium, superconducting rf injector

    SciTech Connect

    T. Rao; I. Ben-Zvi; A. Burrill; H. Hahn; D. Kayran; Y. Zhao; P. Kneisel; M. Cole

    2005-05-16

    Photoelectrons from an all niobium superconducting injector have been generated for the first time. QE of 2 x 10{sup -6} at 266 nm and 2 x 10{sup -5} at 248 nm, maximum charge of 10 nC in 10 ns and charge/cycle of 0.8 nC were measured. The lower QE observed after laser cleaning, compared to the room temperature measurements, is attributed to the long distance between the cathode and the closest ion pump and the possibility of the laser ablated material adsorbed back onto the cathode surface at cryogenic temperature. No cavity quenching has been observed even at the maximum laser energy of 3 mJ, maximum repetition rate of 250 Hz and maximum charge of 10 nC from the cathode.

  7. PHOTOEMISSION STUDIES ON BNL/AES/JLAB ALL NIOBIUM, SUPERCONDUCTING RF INJECTOR.

    SciTech Connect

    RAO, T.; BEN-ZVI, I.; BURRILL, A.; HAHN, H.; KAYRAN, D.; ZHAO, Y.; ET AL.

    2005-05-16

    Photoelectrons from an all niobium superconducting injector have been generated for the first time. QE of 2 x 10{sup -6} at 266 nm and 2 x 10{sup -5} at 248 nm, maximum charge of 10 nC in 10 ns and charge/cycle of 0.8 nC were measured. The lower QE observed after laser cleaning, compared to the room temperature measurements, is attributed to the long distance between the cathode and the closest ion pump and the possibility of the laser ablated material adsorbed back onto the cathode surface at cryogenic temperature. No cavity quenching has been observed even at the maximum laser energy of 3 mJ, maximum repetition rate of 250 Hz and maximum charge of 10 nC from the cathode.

  8. Defect-controlled vortex generation in current-carrying narrow superconducting strips

    NASA Astrophysics Data System (ADS)

    Vodolazov, D. Yu; Ilin, K.; Merker, M.; Siegel, M.

    2016-02-01

    We experimentally study the effect of a single circular hole on the critical current I c of narrow superconducting strip with width W much smaller than Pearl penetration depth Λ. We found non-monotonous dependence of I c on the location of a hole across the strip and a weak dependence of I c on the radius of a hole in the case of a hole with ξ \\ll R\\ll W (ξ is a superconducting coherence length) which is placed in the center of strip. The observed effects are caused by competition of two mechanisms of destruction of superconductivity—the entrance of vortex via the edge of the strip and the nucleation of the vortex-antivortex pair near the hole. The mechanisms are clearly distinguishable by a difference in dependence of I c on weak magnetic field.

  9. Integrated Surface Topography Characterization of Variously Polished Niobium for Superconducting Particle Accelerators

    SciTech Connect

    Hui Tian, Charles Reece, Michael Kelley, G. Ribeill

    2009-05-01

    As superconducting niobium radio-frequency (SRF) cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on realized performance limitations. Micro-and nano-roughness are implicated in both direct geometrical field enhancements as well as complications of the composition of the 50 nm surface layer in which the super-currents flow. Interior surface chemical polishing (BCP/EP) to remove mechanical damage leaves surface topography, including pits and protrusions of varying sharpness. These may promote RF magnetic field entry, locally quenching superconductivity, so as to degrade cavity performance. A more incisive analysis of surface topography than the widely-used average roughness is needed. In this study, a power spectral density (PSD) approach based on Fourier analysis of surface topography data acquired by both stylus profilometry and atomic force microscopy (AFM) is being used to distinguish the scale-dependent smoothing effects. The topographical evolution of the Nb surface as a function of different steps of EP is reported, resulting in a novel qualitative and quantitative description of Nb surface topography.

  10. A novel approach to characterizing the surface topography of niobium superconducting radio frequency (SRF) accelerator cavities

    SciTech Connect

    Hui Tian, Guilhem Ribeill, Chen Xu, Charles E. Reece, Michael J. Kelley

    2011-03-01

    As superconducting niobium radio-frequency (SRF) cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on realized performance limitations. Micro- and nano-roughness are implicated in both direct geometrical field enhancements as well as complications of the composition of the 50 nm surface layer in which the super-currents typically flow. Interior surface chemical treatments such as buffered chemical polishing (BCP) and electropolishing (EP) used to remove mechanical damage leave surface topography, including pits and protrusions of varying sharpness. These may promote RF magnetic field entry, locally quenching superconductivity, so as to degrade cavity performance. A more incisive analysis of surface topography than the widely used average roughness is needed. In this study, a power spectral density (PSD) approach based on Fourier analysis of surface topography data acquired by both stylus profilometry and atomic force microscopy (AFM) is introduced to distinguish the scale-dependent smoothing effects, resulting in a novel qualitative and quantitative description of Nb surface topography. The topographical evolution of the Nb surface as a function of different steps of well-controlled EP is discussed. This study will greatly help to identify optimum EP parameter sets for controlled and reproducible surface levelling of Nb for cavity production.

  11. Superconducting radio-frequency cavities made from medium and low-purity niobium ingots

    NASA Astrophysics Data System (ADS)

    Ciovati, Gianluigi; Dhakal, Pashupati; Myneni, Ganapati R.

    2016-06-01

    Superconducting radio-frequency cavities made of ingot niobium with residual resistivity ratio (RRR) greater than 250 have proven to have similar or better performance than fine-grain Nb cavities of the same purity, after standard processing. The high purity requirement contributes to the high cost of the material. As superconducting accelerators operating in continuous-wave typically require cavities to operate at moderate accelerating gradients, using lower purity material could be advantageous not only to reduce cost but also to achieve higher Q 0-values. In this contribution we present the results from cryogenic RF tests of 1.3–1.5 GHz single-cell cavities made of ingot Nb of medium (RRR = 100–150) and low (RRR = 60) purity from different suppliers. Cavities made of medium-purity ingots routinely achieved peak surface magnetic field values greater than 70 mT with an average Q 0-value of 2 × 1010 at 2 K after standard processing treatments. The performances of cavities made of low-purity ingots were affected by significant pitting of the surface after chemical etching.

  12. Superconducting radio-frequency cavities made from medium and low-purity niobium ingots

    DOE PAGESBeta

    Ciovati, Gianluigi; Dhakal, Pashupati; Myneni, Ganapati R.

    2016-04-07

    Superconducting radio-frequency cavities made of ingot niobium with residual resistivity ratio (RRR) greater than 250 have proven to have similar or better performance than fine-grain Nb cavities of the same purity, after standard processing. The high purity requirement contributes to the high cost of the material. As superconducting accelerators operating in continuous-wave typically require cavities to operate at moderate accelerating gradients, using lower purity material could be advantageous not only to reduce cost but also to achieve higher Q0-values. In this contribution we present the results from cryogenic RF tests of 1.3–1.5 GHz single-cell cavities made of ingot Nb ofmore » medium (RRR = 100–150) and low (RRR = 60) purity from different suppliers. Cavities made of medium-purity ingots routinely achieved peak surface magnetic field values greater than 70 mT with an average Q0-value of 2 × 1010 at 2 K after standard processing treatments. As a result, the performances of cavities made of low-purity ingots were affected by significant pitting of the surface after chemical etching.« less

  13. Preliminary studies of Electric and Magnetic Field Effects in Superconducting Niobium Cavities

    SciTech Connect

    Gianluigi Ciovati; Peter Kneisel; Ganapati Myneni; Jacek Sekutowicz; A. Brinkmann; W. Singer; J. Halbritter

    2003-05-01

    Superconducting cavities made from high purity niobium with RRR > 200 often show pronounced features in the Q vs. E{sub acc} dependence such as a peak at low gradients, a B{sup 2}-slope at intermediate fields and a steep degradation of Q-values (''Q-drop'') at gradients above E{sub acc} {approx} 20 MV/m without field emission loading. Whereas the B{sup 2}-slope is in line with ''global'' heating [2] there are still different models to explain the observed ''Q-drop''. The model of ref. [1] is based on magnetic field enhancements at grain boundaries in the equator weld region of the cavity and local heating. These grain boundaries become normal conducting, when their critical magnetic field is reached and contribute gradually to the losses in the cavity as long as they are thermally stable. The model proposed in ref. [2] is based on effects taking place in the metal-oxide interface on the niobium surface. The major contribution to the RF absorption is coming from interface tunnel exchange between electronic states of superconducting Nb with their energy gap and localized states of the dielectric Nb{sub 2}O{sub 5}. An experimental program was started at JLab to settle the mechanisms behind B{sup 2}-slope and the Q-drop. A modified CEBAF single cell cavity is excited in either TM{sub 010} or TE{sub 011} modes and the Q vs. E{sub acc} dependences are measured as a function of various surface treatments such as BCP, electropolishing, high temperature heat treatment and ''in-situ'' baking. In addition, a special two-cell cavity was designed, which allows the excitation of the 0- and {pi}-modes of the TM{sub 010} passband, which ''scan'' different areas of the cavity surface with high electric and magnetic fields, respectively. This contribution reports about the design and first measurements with both types of cavities.

  14. Conversion gain and noise of niobium superconducting hot-electron-mixers

    NASA Technical Reports Server (NTRS)

    Ekstrom, Hans; Karasik, Boris S.; Kollberg, Erik L.; Yngvesson, Sigfrid

    1995-01-01

    A study has been done of microwave mixing at 20 GHz using the nonlinear (power dependent) resistance of thin niobium strips in the resistive state. Our experiments give evidence that electron-heating is the main cause of the nonlinear phenomenon. Also a detailed phenomenological theory for the determination of conversion properties is presented. This theory is capable of predicting the frequency-conversion loss rather accurately for arbitrary bias by examining the I-V-characteristic. Knowing the electron temperature relaxation time, and using parameters derived from the I-V-characteristic also allows us to predict the -3 dB IF bandwidth. Experimental results are in excellent agreement with the theoretical predictions. The requirements on the mode of operation and on the film parameters for minimizing the conversion loss (and even achieving conversion gain) are discussed in some detail. Our measurements demonstrate an intrinsic conversion loss as low as 1 dB. The maximum IF frequency defined for -3 dB drop in conversion gain, is about 80 MHz. Noise measurements indicate a device output noise temperature of about 50 K and SSB mixer noise temperature below 250 K. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies.

  15. Peak effect phenomena, surface superconductivity and paramagnetic Meissner effect in a spherical single crystal of niobium

    NASA Astrophysics Data System (ADS)

    Das, Pradip; Tomy, C. V.; Takeya, H.; Ramakrishnan, S.; Grover, A. K.

    2009-03-01

    We have explored the vortex phase diagram in a spherical single crystal of niobium (Tc ~ 9.3 K) via isothermal and temperature dependent dc magnetization and ac-susceptibility measurements. The crystal has extremely weak pinning that can be inferred from the reversibility of M - H loops below Tc. However, one can visualize the peak effect (PE) feature in the isothermal M - H loops up to T = 8 K. The PE is also prominent in isothermal ac-susceptibility data for H > 750 Oe. An interesting observation in the present study is the prominent fingerprints of surface superconductivity, starting just above the collapse of pinning at the peak position of the PE and ending at the surface critical field (Hc3). We have also observed the paramagnetic Meissner effect in field-cooled magnetization data recorded at relatively large fields in this crystal. A vortex phase diagram is constructed by marking the peak positions of the PE (Hp), the upper critical field (Hc2) and the surface critical field (Hc3). Unlike a previous report which shows the existence of a multi-critical point in the phase diagram of a Nb crystal, where Hp, Hc2 and Hc3 lines meet, we do not observe a multi-critical point in our weak pinning crystal.

  16. Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

    NASA Astrophysics Data System (ADS)

    Eozénou, F.; Boudigou, Y.; Carbonnier, P.; Charrier, J.-P.; Gasser, Y.; Maurice, L.; Peauger, F.; Roudier, D.; Servouin, C.; Muller, K.

    2014-08-01

    An advanced setup for vertical electropolishing of superconducting radio-frequency niobium elliptical cavities has been installed at CEA Saclay. Cavities are vertically electropolished with circulating standard HF-HF-H2SO4 electrolytes. Parameters such as voltage, cathode shape, acid flow, and temperature have been investigated. A low voltage (between 6 and 10 V depending on the cavity geometry), a high acid flow (25 L /min), and a low acid temperature (20° C) are considered as promising parameters. Such a recipe has been tested on single-cell and nine-cell International Linear Collider (ILC) as well as 704 MHz five-cell Super Proton Linac (SPL) cavities. Single-cell cavities showed similar performances at 1.6 K being either vertically or horizontally electropolished. The applied baking process provides similar benefit. An asymmetric removal is observed with faster removal in the upper half-cells. Multicell cavities (nine-cell ILC and five-cell SPL cavities) exhibit a standard Q0 value at low and medium accelerating fields though limited by power losses due to field emitted electrons.

  17. Effect of non-uniform surface resistance on the quality factor of superconducting niobium cavity

    NASA Astrophysics Data System (ADS)

    Tan, Weiwei; Lu, Xiangyang; Yang, Ziqin; Zhao, Jifei; Yang, Deyu; Yang, Yujia

    2016-08-01

    The formula Rs = G /Q0 is commonly used in the calculation of the surface resistance of radio frequency niobium superconducting cavities. The applying of such equation is under the assumption that surface resistance is consistent over the cavity. However, the distribution of the magnetic field varies over the cavity. The magnetic field in the equator is much higher than that in the iris. According to Thermal Feedback Theory, it leads non-uniform distribution of the density of heat flux, which results in a different temperature distribution along the cavity inter surface. The BCS surface resistance, which depends largely on the temperature, is different in each local inner surface. In this paper, the effect of surface non-uniform resistance on the quality factor has been studied, through the calculation of Q0 in the original definition of it. The results show that it is necessary to consider the non-uniform distribution of magnetic field when the accelerating field is above 20 MV/m for TESLA cavities. Also, the effect of inhomogeneity of residual resistance on the quality factor is discussed. Its distribution barely affects the quality factor.

  18. Ultra-high quality factors in superconducting niobium cavities in ambient magnetic fields up to 190 mG

    NASA Astrophysics Data System (ADS)

    Romanenko, A.; Grassellino, A.; Crawford, A. C.; Sergatskov, D. A.; Melnychuk, O.

    2014-12-01

    Ambient magnetic field, if trapped in the penetration depth, leads to the residual resistance and therefore sets the limit for the achievable quality factors in superconducting niobium resonators for particle accelerators. Here, we show that a complete expulsion of the magnetic flux can be performed and leads to: (1) record quality factors Q > 2 × 1011 up to accelerating gradient of 22 MV/m; (2) Q ˜ 3 × 1010 at 2 K and 16 MV/m in up to 190 mG magnetic fields. This is achieved by large thermal gradients at the normal/superconducting phase front during the cooldown. Our findings open up a way to ultra-high quality factors at low temperatures and show an alternative to the sophisticated magnetic shielding implemented in modern superconducting accelerators.

  19. Ultra-high quality factors in superconducting niobium cavities in ambient magnetic fields up to 190 mG

    SciTech Connect

    Romanenko, A. Grassellino, A.; Crawford, A. C.; Sergatskov, D. A.; Melnychuk, O.

    2014-12-08

    Ambient magnetic field, if trapped in the penetration depth, leads to the residual resistance and therefore sets the limit for the achievable quality factors in superconducting niobium resonators for particle accelerators. Here, we show that a complete expulsion of the magnetic flux can be performed and leads to: (1) record quality factors Q > 2 × 10{sup 11} up to accelerating gradient of 22 MV/m; (2) Q ∼ 3 × 10{sup 10} at 2 K and 16 MV/m in up to 190 mG magnetic fields. This is achieved by large thermal gradients at the normal/superconducting phase front during the cooldown. Our findings open up a way to ultra-high quality factors at low temperatures and show an alternative to the sophisticated magnetic shielding implemented in modern superconducting accelerators.

  20. Etching of Niobium Sample Placed on Superconducting Radio Frequency Cavity Surface in Ar/CL2 Plasma

    SciTech Connect

    Janardan Upadhyay, Larry Phillips, Anne-Marie Valente

    2011-09-01

    Plasma based surface modification is a promising alternative to wet etching of superconducting radio frequency (SRF) cavities. It has been proven with flat samples that the bulk Niobium (Nb) removal rate and the surface roughness after the plasma etchings are equal to or better than wet etching processes. To optimize the plasma parameters, we are using a single cell cavity with 20 sample holders symmetrically distributed over the cell. These holders serve the purpose of diagnostic ports for the measurement of the plasma parameters and for the holding of the Nb sample to be etched. The plasma properties at RF (100 MHz) and MW (2.45 GHz) frequencies are being measured with the help of electrical and optical probes at different pressures and RF power levels inside of this cavity. The niobium coupons placed on several holders around the cell are being etched simultaneously. The etching results will be presented at this conference.

  1. Niobium thin films are superconductive in strong magnetic fields at low temperatures

    NASA Technical Reports Server (NTRS)

    Clough, P. J.; Fowler, P.

    1966-01-01

    Niobium film superconductor carries high currents in strong magnetic fields. The thin niobium film is formed on an inert substrate through evaporation in a vacuum environment. Control of temperature and vacuum results in rejection of gaseous impurities so that the film is of a very high purity.

  2. Observations of flux motion in niobium films. [study of magnetic field trapped in superconducting coatings of gyroscope rotor

    NASA Technical Reports Server (NTRS)

    Xiao, Y. M.; Keiser, G. M.

    1991-01-01

    A magnetic field trapped in a superconducting sphere was examined at temperatures from 4.6 K to 5.5 K. The sphere was the rotor of a precision gyroscope and was made of fused quartz and coated with a sputtered niobium film. The rotor diameter was 3.8 cm. The film thickness was 2.5 microns. The tests were carried out at an ambient magnetic field of about 1 mG. Unexpected instability of the trapped field was observed. The experimental results and possible explanations are presented.

  3. Enhanced Field Emission Studies on Niobium Surfaces Relevant to High Field Superconducting Radio-Frequency Devices

    SciTech Connect

    Tong Wang

    2002-09-18

    Enhanced field emission (EFE) presents the main impediment to higher acceleration gradients in superconducting niobium (Nb) radiofrequency cavities for particle accelerators. The strength, number and sources of EFE sites strongly depend on surface preparation and handling. The main objective of this thesis project is to systematically investigate the sources of EFE from Nb, to evaluate the best available surface preparation techniques with respect to resulting field emission, and to establish an optimized process to minimize or eliminate EFE. To achieve these goals, a scanning field emission microscope (SFEM) was designed and built as an extension to an existing commercial scanning electron microscope (SEM). In the SFEM chamber of ultra high vacuum, a sample is moved laterally in a raster pattern under a high voltage anode tip for EFE detection and localization. The sample is then transferred under vacuum to the SEM chamber equipped with an energy-dispersive x-ray spectrometer for individual emitting site characterization. Compared to other systems built for similar purposes, this apparatus has low cost and maintenance, high operational flexibility, considerably bigger scan area, as well as reliable performance. EFE sources from planar Nb have been studied after various surface preparation, including chemical etching and electropolishing, combined with ultrasonic or high-pressure water rinse. Emitters have been identified, analyzed and the preparation process has been examined and improved based on EFE results. As a result, field-emission-free or near field-emission-free surfaces at ~140 MV/m have been consistently achieved with the above techniques. Characterization on the remaining emitters leads to the conclusion that no evidence of intrinsic emitters, i.e., no fundamental electric field limit induced by EFE, has been observed up to ~140 MV/m. Chemically etched and electropolished Nb are compared and no significant difference is observed up to ~140 MV/m. To

  4. A New Vacuum Brazing Route for Niobium-316L Stainless Steel Transition Joints for Superconducting RF Cavities

    NASA Astrophysics Data System (ADS)

    Kumar, Abhay; Ganesh, P.; Kaul, R.; Bhatnagar, V. K.; Yedle, K.; Ram Sankar, P.; Sindal, B. K.; Kumar, K. V. A. N. P. S.; Singh, M. K.; Rai, S. K.; Bose, A.; Veerbhadraiah, T.; Ramteke, S.; Sridhar, R.; Mundra, G.; Joshi, S. C.; Kukreja, L. M.

    2015-02-01

    The paper describes a new approach for vacuum brazing of niobium-316L stainless steel transition joints for application in superconducting radiofrequency cavities. The study exploited good wettability of titanium-activated silver-base brazing alloy (CuSil-ABA®), along with nickel as a diffusion barrier, to suppress brittle Fe-Nb intermetallic formation, which is well reported during the established vacuum brazing practice using pure copper filler. The brazed specimens displayed no brittle intermetallic layers on any of its interfaces, but instead carried well-distributed intermetallic particles in the ductile matrix. The transition joints displayed room temperature tensile and shear strengths of 122-143 MPa and 80-113 MPa, respectively. The joints not only exhibited required hermeticity (helium leak rate <1.1 × 10-10 mbar l/s) for service in ultra-high vacuum but also withstood twelve hour degassing heat treatment at 873 K (suppresses Q-disease in niobium cavities), without any noticeable degradation in the microstructure and the hermeticity. The joints retained their leak tightness even after undergoing ten thermal cycles between the room temperature and the liquid nitrogen temperature, thereby establishing their ability to withstand service-induced low cycle fatigue conditions. The study proposes a new lower temperature brazing route to form niobium-316L stainless steel transition joints, with improved microstructural characteristics and acceptable hermeticity and mechanical properties.

  5. Topographic power spectral density study of the effect of surface treatment processes on niobium for superconducting radio frequency accelerator cavities

    SciTech Connect

    Charles Reece, Hui Tian, Michael Kelley, Chen Xu

    2012-04-01

    Microroughness is viewed as a critical issue for attaining optimum performance of superconducting radio frequency accelerator cavities. The principal surface smoothing methods are buffered chemical polish (BCP) and electropolish (EP). The resulting topography is characterized by atomic force microscopy (AFM). The power spectral density (PSD) of AFM data provides a more thorough description of the topography than a single-value roughness measurement. In this work, one dimensional average PSD functions derived from topography of BCP and EP with different controlled starting conditions and durations have been fitted with a combination of power law, K correlation, and shifted Gaussian models to extract characteristic parameters at different spatial harmonic scales. While the simplest characterizations of these data are not new, the systematic tracking of scale-specific roughness as a function of processing is new and offers feedback for tighter process prescriptions more knowledgably targeted at beneficial niobium topography for superconducting radio frequency applications.

  6. Vortex Properties of Nanosized Superconducting Strips with One Central Weak Link Under an Applied Current Drive

    NASA Astrophysics Data System (ADS)

    Peng, Lin; Cai, Chuanbing

    2016-06-01

    The static and dynamic properties of vortices in a nanosized superconducting strip with one central weak link (weakly superconducting region or normal metal) are investigated in the presence of external magnetic and electric fields. The time-dependent Ginzburg-Landau equations are used to describe the electronic transport and have been solved numerically by a finite element analysis. Anisotropy is included through the spatially dependent anisotropy coefficient ζ in different layers of the sample. Our results show that the energy barrier for vortices to enter a weak link is smaller than that for vortices to enter the superconducting layers. The magnetization shows periodic oscillations. With the introduction of the weak link, the period of oscillations decreases.

  7. Passivated niobium cavities

    DOEpatents

    Myneni, Ganapati Rao; Hjorvarsson, Bjorgvin; Ciovati, Gianluigi

    2006-12-19

    A niobium cavity exhibiting high quality factors at high gradients is provided by treating a niobium cavity through a process comprising: 1) removing surface oxides by plasma etching or a similar process; 2) removing hydrogen or other gases absorbed in the bulk niobium by high temperature treatment of the cavity under ultra high vacuum to achieve hydrogen outgassing; and 3) assuring the long term chemical stability of the niobium cavity by applying a passivating layer of a superconducting material having a superconducting transition temperature higher than niobium thereby reducing losses from electron (cooper pair) scattering in the near surface region of the interior of the niobium cavity. According to a preferred embodiment, the passivating layer comprises niobium nitride (NbN) applied by reactive sputtering.

  8. Thicker, more efficient superconducting strip-line detectors for high throughput macromolecules analysis

    SciTech Connect

    Casaburi, A.; Ejrnaes, M.; Cristiano, R.; Zen, N.; Ohkubo, M.; Pagano, S.

    2011-01-10

    Fast detectors with large area are required in time-of-flight mass spectrometers for high throughput analysis of biological molecules. We fabricated and characterized subnanosecond 1x1 mm{sup 2} NbN superconducting strip-line detectors. The influence of the strip-line thickness on the temporal characteristics and efficiency of the detector for the impacts of keV accelerated molecules is investigated. We find that the increase of thickness improves both efficiency and response time. In the thicker sample we achieved a rise time of 380 ps, a fall time of 1.38 ns, and a higher count rate. The physics involved in this behavior is investigated.

  9. Interaction of Josephson Junction and Distant Vortex in Narrow Thin-Film Superconducting Strips

    SciTech Connect

    Kogan, V. G.; Mints, R. G.

    2014-01-31

    The phase difference between the banks of an edge-type planar Josephson junction crossing the narrow thin-film strip depends on wether or not vortices are present in the junction banks. For a vortex close to the junction this effect has been seen by Golod, Rydh, and Krasnov [Phys. Rev. Lett. 104, 227003 (2010)], who showed that the vortex may turn the junction into π type. It is shown here that even if the vortex is far away from the junction, it still changes the 0 junction to a π junction when situated close to the strip edges. Within the approximation used, the effect is independent of the vortex-junction separation, a manifestation of the topology of the vortex phase which extends to macroscopic distances of superconducting coherence.

  10. Biomolecular ion detection using high-temperature superconducting MgB2 strips

    NASA Astrophysics Data System (ADS)

    Zen, N.; Shibata, H.; Mawatari, Y.; Koike, M.; Ohkubo, M.

    2015-06-01

    Superconducting strip ion detectors (SSIDs) are promising for realization of ideal ion detection with 100% efficiency and nanosecond-scale time response in time-of-flight mass spectrometry. We have detected single biomolecular ions in the keV range using a 10-nm-thick and 250-nm-wide strip of a high temperature superconductor, magnesium diboride (MgB2), at temperatures of up to 13 K. The output pulse shape is explained remarkably well using circuit simulations and time-dependent Ginzburg-Landau simulations coupled with a heat diffusion equation. The simulations show that the hot spot model is applicable to the proposed MgB2-SSIDs and the normal region expansion is completed within 16 ps, which corresponds to a maximum length of 1010 nm.

  11. An improved oxygen diffusion model to explain the effect of low-temperature baking on high field losses in niobium superconducting cavities

    SciTech Connect

    Ciovati, Gianluigi

    2006-07-01

    Radio-frequency (RF) superconducting cavities made of high purity niobium are widely used to accelerate charged particle beams in particle accelerators. The major limitation to achieve RF field values approaching the theoretical limit for niobium is represented by ''anomalous'' losses which degrade the quality factor of the cavities starting at peak surface magnetic fields of about 100 mT, in absence of field emission. These high field losses are often referred to as ''Q-drop''. It has been observed that the Q-drop is drastically reduced by baking the cavities at 120 C for about 48 h under ultrahigh vacuum. An improved oxygen diffusion model for the niobium-oxide system is proposed to explain the benefit of the low-temperature baking on the Q-drop in niobium superconducting rf cavities. The model shows that baking at 120 C for 48 h allows oxygen to diffuse away from the surface, and therefore increasing the lower critical field towards the value for pure niobium.

  12. The First Observation of Intra Beam Stripping of Negative Hydrogen in a Superconducting Linear Accelerator

    SciTech Connect

    Aleksandrov, Alexander V; Plum, Michael A; Shishlo, Andrei P; Galambos, John D

    2012-01-01

    We report on an experiment in which a negative hydrogen ions beam in the Spallation Neutron Source (SNS) linear accelerator was replaced with a beam of protons with similar size and dynamics. Beam loss in the superconducting part of the SNS accelerator was at least an order of magnitude lower for the proton beam. Also beam loss has a stronger dependence on intensity with H- than with proton beams. These measurements verify a recent theoretical explanation of unexpected beam losses in the SNS superconducting linear accelerator based on an intra beam stripping mechanism for negative hydrogen ions. An identification of the new physics mechanism for beam loss is important for the design of new high current linear ion accelerators and the performance improvement of existing machines

  13. First Observation of Intrabeam Stripping of Negative Hydrogen in a Superconducting Linear Accelerator

    NASA Astrophysics Data System (ADS)

    Shishlo, A.; Galambos, J.; Aleksandrov, A.; Lebedev, V.; Plum, M.

    2012-03-01

    We report on an experiment in which a negative hydrogen ion beam in the Spallation Neutron Source (SNS) linear accelerator was replaced with a beam of protons with similar size and dynamics. Fractional beam loss in the superconducting part of the SNS accelerator was measured to be at least 2×10-5 for the H- beam, and it was an order of magnitude lower for the protons. Also beam loss has a stronger dependence on intensity with H- than with proton beams. These measurements verify a recent theoretical explanation of unexpected beam losses in the SNS superconducting linear accelerator based on an intrabeam stripping mechanism for negative hydrogen ions. This previously unidentified mechanism for beam loss is important for the design of new high current linear ion accelerators and the performance improvement of existing machines.

  14. Evaluation of the Propensity of Niobium to Absorb Hydrogen During Fabrication of Superconducting Radio Frequency Cavities for Particle Accelerators

    PubMed Central

    Ricker, R. E.; Myneni, G. R.

    2010-01-01

    During the fabrication of niobium superconducting radio frequency (SRF) particle accelerator cavities procedures are used that chemically or mechanically remove the passivating surface film of niobium pentoxide (Nb2O5). Removal of this film will expose the underlying niobium metal and allow it to react with the processing environment. If these reactions produce hydrogen at sufficient concentrations and rates, then hydrogen will be absorbed and diffuse into the metal. High hydrogen activities could result in supersaturation and the nucleation of hydride phases. If the metal repassivates at the conclusion of the processing step and the passive film blocks hydrogen egress, then the absorbed hydrogen or hydrides could be retained and alter the performance of the metal during subsequent processing steps or in-service. This report examines the feasibility of this hypothesis by first identifying the postulated events, conditions, and reactions and then determining if each is consistent with accepted scientific principles, literature, and data. Established precedent for similar events in other systems was found in the scientific literature and thermodynamic analysis found that the postulated reactions were not only energetically favorable, but produced large driving forces. The hydrogen activity or fugacity required for the reactions to be at equilibrium was determined to indicate the propensity for hydrogen evolution, absorption, and hydride nucleation. The influence of processing conditions and kinetics on the proximity of hydrogen surface coverage to these theoretical values is discussed. This examination found that the hypothesis of hydrogen absorption during SRF processing is consistent with published scientific literature and thermodynamic principles. PMID:27134791

  15. Impact of nitrogen doping of niobium superconducting cavities on the sensitivity of surface resistance to trapped magnetic flux

    NASA Astrophysics Data System (ADS)

    Gonnella, Dan; Kaufman, John; Liepe, Matthias

    2016-02-01

    Future particle accelerators such as the SLAC "Linac Coherent Light Source-II" (LCLS-II) and the proposed Cornell Energy Recovery Linac require hundreds of superconducting radio-frequency (SRF) niobium cavities operating in continuous wave mode. In order to achieve economic feasibility of projects such as these, the cavities must achieve a very high intrinsic quality factor (Q0) to keep cryogenic losses within feasible limits. To reach these high Q0's in the case of LCLS-II, nitrogen-doping of niobium cavities has been selected as the cavity preparation technique. When dealing with Q0's greater than 1 × 1010, the effects of ambient magnetic field on Q0 become significant. Here, we show that the sensitivity to RF losses from trapped magnetic field in a cavity's walls is strongly dependent on the cavity preparation. Specifically, standard electropolished and 120 °C baked cavities show a sensitivity of residual resistance from trapped magnetic flux of ˜0.6 and ˜0.8 nΩ/mG trapped, respectively, while nitrogen-doped cavities show a higher sensitivity of residual resistance from trapped magnetic flux of ˜1 to 5 nΩ/mG trapped. We show that this difference in sensitivities is directly related to the mean free path of the RF surface layer of the niobium: shorter mean free paths lead to less sensitivity of residual resistance to trapped magnetic flux in the dirty limit (ℓ ≪ ξ0), while longer mean free paths lead to lower sensitivity of residual resistance to trapped magnetic flux in the clean limit (ℓ ≫ ξ0). These experimental results are also shown to have good agreement with recent theoretical predictions for pinned vortex lines oscillating in RF fields.

  16. Quantum and thermal phase slips in superconducting niobium nitride (NbN) ultrathin crystalline nanowire: application to single photon detection.

    PubMed

    Delacour, Cécile; Pannetier, Bernard; Villegier, Jean-Claude; Bouchiat, Vincent

    2012-07-11

    We present low-temperature electronic transport properties of superconducting nanowires obtained by nanolithography of 4-nm-thick niobium nitride (NbN) films epitaxially grown on sapphire substrate. Below 6 K, clear evidence of phase slippages is observed in the transport measurements. Upon lowering the temperature, we observe the signatures of a crossover between a thermal and a quantum behavior in the phase slip regimes. We find that phase slips are stable even at the lowest temperatures and that no hotspot is formed. The photoresponse of these nanowires is measured as a function of the light irradiation wavelength and temperature and exhibits a behavior comparable with previous results obtained on thicker films. PMID:22694480

  17. Investigating ion-surface collisions with a niobium superconducting tunnel junction detector in a time-of-flight mass spectrometer

    SciTech Connect

    Westmacott, G.; Zhong, F.; Frank, M.; Friedrich, S.; Labov, S.; Benner, W.H.

    1999-12-01

    The performance of an energy sensitive, niobium superconducting tunnel junction detector is investigated by measuring the pulse height produced by impacting molecular and atomic ions at different kinetic energies. Ions are produced by laser resorption and matrix-assisted laser desorption in a time-of-flight mass spectrometer. Results show that the STJ detector pulse height decreases for increasing molecular ion mass, passes through a minimum at around 2000 Da, and the increases with increasing mass of molecular ions above 2000Da. The detector does not show a decline in sensitivity for high mass ions as is observed with microchannel plate ion detectors. These detector plus height measurements are discussed in terms of several physical mechanisms involved in an ion-surface collision.

  18. Investigating ion-surface collisions with a niobium superconducting tunnel junction detector in a time-of-flight mass spectrometer

    PubMed

    Westmacott; Zhong; Frank; Friedrich; Labov; Benner

    2000-01-01

    The performance of an energy sensitive, niobium superconducting tunnel junction (STJ) detector is investigated by measuring the pulse height produced by impacting molecular and atomic ions at different kinetic energies. Ions are produced by laser desorption and matrix-assisted laser desorption in a time-of-flight mass spectrometer. Our results show that the STJ detector pulse height decreases for increasing molecular ion mass, passes through a minimum at around 2000 Da, and then increases with increasing mass of molecular ions above 2000 Da. The detector does not show a decline in sensitivity for high mass ions as is observed with microchannel plate ion detectors. These detector plus height measurements are discussed in terms of several physical mechanisms involved in an ion-surface collision. PMID:10775095

  19. Production of Seamless Superconducting Radio Frequency Cavities from Ultra-fine Grained Niobium, Phase II Final Report

    SciTech Connect

    Roy Crooks, Ph.D., P.E.

    2009-10-31

    The positron and electron linacs of the International Linear Collider (ILC) will require over 14,000, nine-cell, one meter length, superconducting radio frequency (SRF) cavities [ILC Reference Design Report, 2007]. Manufacturing on this scale will benefit from more efficient fabrication methods. The current methods of fabricating SRF cavities involve deep drawing of the halves of each of the elliptical cells and joining them by high-vacuum, electron beam welding, with at least 19 circumferential welds per cavity. The welding is costly and has undesirable effects on the cavity surfaces, including grain-scale surface roughening at the weld seams. Hydroforming of seamless tubes avoids welding, but hydroforming of coarse-grained seamless tubes results in strain-induced surface roughening. Surface roughness limits accelerating fields, because asperities prematurely exceed the critical magnetic field and become normal conducting. This project explored the technical and economic feasibility of an improved processing method for seamless tubes for hydroforming. Severe deformation of bulk material was first used to produce a fine structure, followed by extrusion and flow-forming methods of tube making. Extrusion of the randomly oriented, fine-grained bulk material proceeded under largely steady-state conditions, and resulted in a uniform structure, which was found to be finer and more crystallographically random than standard (high purity) RRR niobium sheet metal. A 165 mm diameter billet of RRR grade niobium was processed into five, 150 mm I.D. tubes, each over 1.8 m in length, to meet the dimensions used by the DESY ILC hydroforming machine. Mechanical properties met specifications. Costs of prototype tube production were approximately twice the price of RRR niobium sheet, and are expected to be comparable with economies of scale. Hydroforming and superconducting testing will be pursued in subsequent collaborations with DESY and Fermilab. SRF Cavities are used to construct

  20. Possible influence of surface oxides on the optical response of high-purity niobium material used in the fabrication of superconducting radio frequency cavity

    NASA Astrophysics Data System (ADS)

    Singh, Nageshwar; Deo, M. N.; Roy, S. B.

    2016-09-01

    We have investigated the possible influence of surface oxides on the optical properties of a high-purity niobium (Nb) material for fabrication of superconducting radio frequency (SCRF) cavities. Various peaks in the infrared region were identified using Fourier transform infrared and Raman spectroscopy. Optical response functions such as complex refractive index, dielectric and conductivity of niobium were compared with the existing results on oxides free Nb and Cu. It was observed that the presence of a mixture of niobium-oxides, and probably near other surface impurities, appreciably influence the conducting properties of the material causing deviation from the typical metallic characteristics. In this way, the key result of this work is the observation, identification of vibrational modes of some of surface complexes and study of its influences on the optical responses of materials. This method of spectroscopic investigation will help in understanding the origin of degradation of performance of SCRF cavities.

  1. Cold RF test and associated mechanical features correlation of a TESLA-style 9-cell superconducting niobium cavity built in China

    SciTech Connect

    Dai, Jing; Quan, Sheng-Wen; Zhang, Bao-Cheng; Lin, Lin; Hao, Jian-Kui; Zhu, Feng; Xu, Wen-Can; He, Fei-Si; Jin, Song; Wang, Fang; Liu, Ke-Xin; Geng, R L; Zhao, Kui

    2012-02-01

    The RF performance of a 1.3 GHz 9-cell superconducting niobium cavity was evaluated at cryogenic temperatures following surface processing by using the standard ILC-style recipe. The cavity is a TESLA-style 9-cell superconducting niobium cavity, with complete end group components including a higher order mode coupler, built in China for practical applications. An accelerating gradient of 28.6 MV/m was achieved at an unloaded quality factor of 4 x 10{sup 9}. The morphological property of mechanical features on the RF surface of this cavity was characterized through optical inspection. Correlation between the observed mechanical features and the RF performance of the cavity is attempted.

  2. Design of a 10-T superconducting dipole magnet using niobium-tin conductor

    SciTech Connect

    Taylor, C.; Meuser, R.; Caspi, S.; Gilbert, W.; Hassenzahl, W.; Peters, C.; Schafer, R.; Wolgast, R.

    1982-11-01

    In order to minimize the size and cost of conventional facilities - land, tunneling, shielding, cryogenic and vacuum system - the dipole magnets for the next generation of particle accelerators must produce as strong a magnetic field as possible. Ten tesla seems to be a reasonable goal, and can be attained by using either niobium-tin conductor at 4.2 K or niobium-titanium at 1.8 K. The beam diameter in a multi-TeV accelerator, can in principle, be quite small, say 20 mm, depending on the design of the injection and extraction systems, and on beam-cooling technology. Magnet cost is strongly dependent on bore diameter, so there is a strong incentive to minimize that. We believe that a 40-mm bore diameter - about 60-mm winding inside diameter is feasible and is a reasonable goal for initial research and development. For such a high field and small bore, there is an incentive to achieve a high overall current density in order to minimize the amount of superconductor. Our design is based on an overall current density of 400 A/sq mm. LBL has undertaken the development of a magnet using niobium-tin conductor intended to meet the above specifications. The conductor is a Rutherford-type cable consisting of twelve strands of 1.71-mm-dia wire. Dimensions of the uninsulated cable are 11.0 x 3.0 mm. The configuration chosen consists of flat race-track layers - four per pole - with the ends bent up and down to clear the bore. Two coils are wound from a single piece of cable with a cross-over at the inside: the familiar double pancake arrangement.

  3. Self-field effects upon the critical current density of flat superconducting strips

    NASA Astrophysics Data System (ADS)

    Babaei Brojeny, Ali A.; Clem, John R.

    2005-06-01

    We develop a general theory to account self-consistently for self-field effects upon the average transport critical current density Jc of a flat type-II superconducting strip in the mixed state when the bulk pinning is characterized by a field-dependent depinning critical current density Jp(B), where B is the local magnetic flux density. We first consider the possibility of both bulk and edge-pinning contributions but conclude that bulk pinning dominates over geometrical edge-barrier effects in state-of-the-art YBCO films and prototype second-generation coated conductors. We apply our theory using the Kim model, JpK(B) = JpK(0)/(1+|B|/B0), as an example. We calculate Jc(Ba) as a function of a perpendicular applied magnetic induction Ba and show how Jc(Ba) is related to JpK(B). We find that Jc(Ba) is very nearly equal to JpK(Ba) when Ba>=Ba*, where Ba* is the value of Ba that makes the net flux density zero at the strip's edge. However, Jc(Ba) is suppressed relative to JpK(Ba) at low fields when Ba< Ba*, with the largest suppression occurring when Ba*/B0 is of order unity or larger.

  4. Large Superconducting Spin Valve Effect and Ultrasmall Exchange Splitting in Epitaxial Rare-Earth-Niobium Trilayers

    NASA Astrophysics Data System (ADS)

    Gu, Yuanzhou; Halász, Gábor B.; Robinson, J. W. A.; Blamire, M. G.

    2015-08-01

    Epitaxial Ho /Nb /Ho and Dy /Nb /Dy superconducting spin valves show a reversible change in the zero-field critical temperature (Δ Tc 0 ) of ˜400 mK and an infinite magnetoresistance on changing the relative magnetization of the Ho or Dy layers. Unlike transition-metal superconducting spin valves, which show much smaller Δ Tc 0 values, our results can be quantitatively modeled. However, the fits require an extraordinarily low induced exchange splitting which is dramatically lower than known values for rare-earth Fermi-level electrons, implying that new models for the magnetic proximity effect may be required.

  5. Niobium Thin Film Characterization for Thin Film Technology Used in Superconducting Radiofrequency Cavities

    NASA Astrophysics Data System (ADS)

    Dai, Yishu; Valente-Feliciano, Anne-Marie

    2015-10-01

    Superconducting RadioFrequency (SRF) penetrates about 40-100 nm of the top surface, making thin film technology possible in producing superconducting cavities. Thin film is based on the deposition of a thin Nb layer on top of a good thermal conducting material such as Al or Cu. Thin film allows for better control of the surface and has negligible response to the Earth's magnetic field, eliminating the need for magnetic shielding of the cavities. Thin film superconductivity depends heavily on coating process conditions, involving controllable parameters such as crystal plane orientation, coating temperature, and ion energy. MgO and Al2O3 substrates are used because they offer very smooth surfaces, ideal for studying film growth. Atomic Force Microscopy is used to characterize surface's morphology. It is evident that a lower nucleation energy and a long coating time increases the film quality in the r-plane sapphire crystal orientation. The quality of the film increases with thickness. Nb films coated on r-plane, grow along the (001) plane and yield a much higher RRR compared to the films grown on a- and c-planes. This information allows for further improvement on the research process for thin film technology used in superconducting cavities for the particle accelerators. National Science Foundation, Department of Energy, Jefferson Lab, Old Dominion University.

  6. Investigation of local losses as a function of material removal in a large-grain superconducting niobium cavity

    SciTech Connect

    Gianluigi Ciovati; Peter Kneisel

    2006-08-02

    The performance of a superconducting radio-frequency (RF) cavity made of residual resistivity ratio (RRR) > 200 large-grain niobium has been investigated as a function of material removal, between 70 and 240 ?m, by buffered chemical polishing (BCP). Temperature maps of the cavity surface at 1.7 and 2.0 K were taken for each step of chemical etching and revealed localized losses (''hot-spots''), which contribute to the degradation of the cavity quality factor as a function of the RF surface field. It was found that the number of ''hot-spots'' decreased for larger material removal. Interestingly, the losses at the ''hot-spots'' at different locations evolved differently for successive material removal. The cavity achieved peak surface magnetic fields of about of 130 mT and was limited mostly by thermal quench. By measuring the temperature dependence of the surface resistance (Rs) at low field between 4.2 K and 1.7 K, the variation of material parameters such as the energy gap at 0 K, the residual resistance and the mean free path as a function of material removal could also be investigated. This contribution presents the results of the RF tests along with the temperature maps and the analysis of the losses caused by the ''hot-spots''.

  7. Investigation of local losses as a function of material removal in a large-grain superconducting niobium cavity

    SciTech Connect

    G. Ciovati, P. Kneisel

    2008-01-02

    The performance of a superconducting radio-frequency (RF) cavity made of residual resistivity ratio (RRR) > 200 large-grain niobium has been investigated as a function of material removal, between 70 and 240 mu-m, by buffered chemical polishing (BCP). Temperature maps of the cavity surface at 1.7 and 2 K were taken for each step of chemical etching and revealed localized losses (hot-spots), which contribute to the degradation of the cavity quality factor as a function of the RF surface field. It was found that the number of hot-spots decreased for larger material removal. Interestingly, the losses at the hot-spots at different locations evolved differently for successive material removal. The cavity achieved peak surface magnetic fields of about of 130 mT and was limited mostly by thermal quench. By measuring the temperature dependence of the surface resistance (Rs) at low field between 4.2 K and 1.7 K, the variation of material parameters such as the energy gap at 0 K, the residual resistance and the mean free path as a function of material removal could also be investigated. This contribution shows the results of the RF tests along with the temperature maps and the analysis of the losses caused by the "hot-spots."

  8. Characterization of etch pits found on a large-grain bulk niobium superconducting radio-frequency resonant cavity

    DOE PAGESBeta

    Zhao, Xin; Ciovati, G.; Bieler, T. R.

    2010-12-15

    The performance of superconducting radio-frequency (SRF) resonant cavities made of bulk niobium is limited by nonlinear localized effects. Surface analysis of regions of higher power dissipation is thus of intense interest. Such areas (referred to as “hotspots”) were identified in a large-grain single-cell cavity that had been buffered-chemical polished and dissected for examination by high resolution electron microscopy, electron backscattered diffraction microscopy (EBSD), and optical microscopy. Pits with clearly discernible crystal facets were observed in both “hotspot” and “coldspot” specimens. The pits were found in-grain, at bicrystal boundaries, and on tricrystal junctions. They are interpreted as etch pits induced bymore » crystal defects (e.g. dislocations). All coldspots examined had a qualitatively lower density of etch pits or relatively smooth tricrystal boundary junctions. EBSD mapping revealed the crystal orientation surrounding the pits. Locations with high pit density are correlated with higher mean values of the local average misorientation angle distributions, indicating a higher geometrically necessary dislocation content. In addition, a survey of the samples by energy dispersive x-ray analysis did not show any significant contamination of the samples’ surface. In conclusion, the local magnetic field enhancement produced by the sharp-edge features observed on the samples is not sufficient to explain the observed degradation of the cavity quality factor, which starts at peak surface magnetic field as low as 20 mT.« less

  9. Characterization of etch pits found on a large-grain bulk niobium superconducting radio-frequency resonant cavity

    SciTech Connect

    Zhao, Xin; Ciovati, G.; Bieler, T. R.

    2010-12-15

    The performance of superconducting radio-frequency (SRF) resonant cavities made of bulk niobium is limited by nonlinear localized effects. Surface analysis of regions of higher power dissipation is thus of intense interest. Such areas (referred to as “hotspots”) were identified in a large-grain single-cell cavity that had been buffered-chemical polished and dissected for examination by high resolution electron microscopy, electron backscattered diffraction microscopy (EBSD), and optical microscopy. Pits with clearly discernible crystal facets were observed in both “hotspot” and “coldspot” specimens. The pits were found in-grain, at bicrystal boundaries, and on tricrystal junctions. They are interpreted as etch pits induced by crystal defects (e.g. dislocations). All coldspots examined had a qualitatively lower density of etch pits or relatively smooth tricrystal boundary junctions. EBSD mapping revealed the crystal orientation surrounding the pits. Locations with high pit density are correlated with higher mean values of the local average misorientation angle distributions, indicating a higher geometrically necessary dislocation content. In addition, a survey of the samples by energy dispersive x-ray analysis did not show any significant contamination of the samples’ surface. In conclusion, the local magnetic field enhancement produced by the sharp-edge features observed on the samples is not sufficient to explain the observed degradation of the cavity quality factor, which starts at peak surface magnetic field as low as 20 mT.

  10. Large Superconducting Spin Valve Effect and Ultrasmall Exchange Splitting in Epitaxial Rare-Earth-Niobium Trilayers.

    PubMed

    Gu, Yuanzhou; Halász, Gábor B; Robinson, J W A; Blamire, M G

    2015-08-01

    Epitaxial Ho/Nb/Ho and Dy/Nb/Dy superconducting spin valves show a reversible change in the zero-field critical temperature (ΔT(c0)) of ∼400  mK and an infinite magnetoresistance on changing the relative magnetization of the Ho or Dy layers. Unlike transition-metal superconducting spin valves, which show much smaller ΔT(c0) values, our results can be quantitatively modeled. However, the fits require an extraordinarily low induced exchange splitting which is dramatically lower than known values for rare-earth Fermi-level electrons, implying that new models for the magnetic proximity effect may be required. PMID:26296128

  11. Effects of strain on the superconducting properties of niobium-tin conductors

    SciTech Connect

    Hoard, R.W.

    1980-11-01

    Investigations were performed to ascertain additional information on the connection between the cubic to tetragonal martensitic phase transformation and the phenomenon of superconductivity in Nb/sub 3/Sn. Of particular interest is the degradation of the critical parameters, such as T/sub c/, H/sub c2/, and J/sub c/, with mechanical straining of the superconductor. These studies yielded information that assisted in the derivation of the critical current-strain scaling laws mentioned above.

  12. Nanostructural features degrading the performance of superconducting radio frequency niobium cavities revealed by transmission electron microscopy and electron energy loss spectroscopy

    SciTech Connect

    Trenikhina, Y.; Romanenko, A.; Kwon, J.; Zuo, J.-M.; Zasadzinski, J. F.

    2015-04-21

    Nanoscale defect structure within the magnetic penetration depth of ∼100 nm is key to the performance limitations of niobium superconducting radio frequency cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls, we discover the existence of nanoscale hydrides in electropolished cavities limited by the high field Q slope, and show the decreased hydride formation in the electropolished cavity after 120 °C baking. Furthermore, we demonstrate that adding 800 °C hydrogen degassing followed by light buffered chemical polishing restores the hydride formation to the pre-120 °C bake level. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120 °C bake.

  13. Nanostructural features degrading the performance of superconducting radio frequency niobium cavities revealed by transmission electron microscopy and electron energy loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Trenikhina, Y.; Romanenko, A.; Kwon, J.; Zuo, J.-M.; Zasadzinski, J. F.

    2015-04-01

    Nanoscale defect structure within the magnetic penetration depth of ˜100 nm is key to the performance limitations of niobium superconducting radio frequency cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls, we discover the existence of nanoscale hydrides in electropolished cavities limited by the high field Q slope, and show the decreased hydride formation in the electropolished cavity after 120 °C baking. Furthermore, we demonstrate that adding 800 °C hydrogen degassing followed by light buffered chemical polishing restores the hydride formation to the pre-120 °C bake level. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120 °C bake.

  14. Mechanical properties as an indicator of interstitials in niobium for superconducting accelerator cavities

    SciTech Connect

    Ricker, R. E. Pitchure, D. J.; Myneni, G. R.

    2015-12-04

    A preliminary investigation was conducted into the feasibility of using simple mechanical properties experiments to evaluate interstitial impurity uptake from processing environments. Two types of tests were examined: tensile tests and complex modulus measurements using a dynamic mechanical analyzer (DMA). For the tensile tests, samples were cut from a single crystal of niobium, with the same orientation, and then prepared following different procedures. Significant differences were observed during tensile tests, with yielding strength and strain-to-failure clearly related to interstitial uptake. When the strain rate was reduced by an order of magnitude, the strain-to-failure was reduced by 18 % indicating that interstitial hydrogen is responsible for this behavior. For the complex modulus measurement, polycrystalline samples from different locations of two different ingots were examined at a frequency of 1.0 Hz while the temperature was increased at the rate of 1.0 °C per minute. Anaelastic peaks were found for C, N, and O in all samples, but the lower limit of the system did not allow for detection of a peak for H. It is concluded that mechanical properties could be developed as a measurement tool to guide the development of processing methods for producing reduced interstitial content material, but additional research, and uncertainty analysis, is required for these tools to be reliable in this application.

  15. Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field

    NASA Astrophysics Data System (ADS)

    Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe

    2013-12-01

    We present an exact analytical approach for arbitrary field-dependent critical state of high-Tc superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the Ia-Ba plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.

  16. Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field

    SciTech Connect

    Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe

    2013-12-15

    We present an exact analytical approach for arbitrary field-dependent critical state of high-T{sub c} superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the I{sub a}-B{sub a} plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.

  17. Probing the low-frequency vortex dynamics in a nanostructured superconducting strip

    NASA Astrophysics Data System (ADS)

    Silva, C. C. de Souza; Raes, B.; Brisbois, J.; Cabral, L. R. E.; Silhanek, A. V.; Van de Vondel, J.; Moshchalkov, V. V.

    2016-07-01

    We investigate by scanning susceptibility microscopy the response of a thin Pb strip, with a square array of submicron antidots, to a low-frequency ac magnetic field applied perpendicularly to the film plane. By mapping the local permeability of the sample within the field range where vortices trapped by the antidots and interstitial vortices coexist, we observed two distinct dynamical regimes occurring at different temperatures. At a temperature just below the superconducting transition, T /Tc=0.96 , the sample response is essentially dominated by the motion of highly mobile interstitial vortices. However, at a slightly lower temperature, T /Tc=0.93 , the interstitial vortices freeze up leading to a strong reduction of the ac screening length. We propose a simple model for the vortex response in this system which fits well to the experimental data. Our analysis suggests that the observed switching to the high mobility regime stems from a resonant effect, where the period of the ac excitation is just large enough to allow interstitial vortices to thermally hop through the weak pinning landscape produced by random material defects. This argument is further supported by the observation of a pronounced enhancement of the out-of-phase response at the crossover between both dynamical regimes.

  18. Field-History Dependence of the Superconducting Transition Temperature in Erbium/Niobium Bilayers

    NASA Astrophysics Data System (ADS)

    Witt, James; Satchell, Nathan; Langridge, Sean; Burnell, Gavin

    Recently, there has been much interest in a new class of superconducting (S) spintronic devices based upon hybrid S/F (ferromagnet) heterostructures. The prototypical super-spintronic device is the superconducting spin valve (SSV), within which the critical temperature (Tc) of an S layer can be controlled by the relative orientation of two or more F layers. Such manipulation of the F layers requires careful engineering of the heterostructure and the rotation of the structure with respect to an applied magnetic field. Here, we show that such control over Tc is also possible in a simple S/F bilayer. By manipulating the remenant magnetic state of a thin Er layer - which is proximity coupled to a Nb S layer - we are able to demonstrate a high level of control over the Tc of the Nb (which is measured in zero field). The shifts in Tc are comparable in size to the largest seen in the SSV and are manipulated using solely the field history. The system can be reset by warming the sample through the Er Curie temperature (approximately 20 K). Our results are of particular interest due to the simplicity of both the bilayer and the measurement geometry in comparison to the SSV.

  19. Parallel Configuration For Fast Superconducting Strip Line Detectors With Very Large Area In Time Of Flight Mass Spectrometry

    SciTech Connect

    Casaburi, A.; Zen, N.; Suzuki, K.; Ohkubo, M.; Ejrnaes, M.; Cristiano, R.; Pagano, S.

    2009-12-16

    We realized a very fast and large Superconducting Strip Line Detector based on a parallel configuration of nanowires. The detector with size 200x200 {mu}m{sup 2} recorded a sub-nanosecond pulse width of 700 ps in FWHM (400 ps rise time and 530 ps relaxation time) for lysozyme monomers/multimers molecules accelerated at 175 keV in a Time of Flight Mass Spectrometer. This record is the best in the class of superconducting detectors and comparable with the fastest NbN superconducting single photon detector of 10x10 {mu}m{sup 2}. We succeeded in acquiring mass spectra as the first step for a scale-up to {approx}mm pixel size for high throughput MS analysis, while keeping a fast response.

  20. Hybrid superconducting neutron detectors

    SciTech Connect

    Merlo, V.; Lucci, M.; Ottaviani, I.; Salvato, M.; Cirillo, M.; Scherillo, A.; Celentano, G.; Pietropaolo, A.

    2015-03-16

    A neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction, {sup 10}B + n → α + {sup 7}Li, with α and Li ions generating a hot spot on the current-biased Nb strip which in turn induces a superconducting-normal state transition. The latter is recognized as a voltage signal which is the evidence of the incident neutron. The above described detection principle has been experimentally assessed and verified by irradiating the samples with a pulsed neutron beam at the ISIS spallation neutron source (UK). It is found that the boron coated superconducting strips, kept at a temperature T = 8 K and current-biased below the critical current I{sub c}, are driven into the normal state upon thermal neutron irradiation. As a result of the transition, voltage pulses in excess of 40 mV are measured while the bias current can be properly modulated to bring the strip back to the superconducting state, thus resetting the detector. Measurements on the counting rate of the device are presented and the basic physical features of the detector are discussed.

  1. Hybrid superconducting neutron detectors

    NASA Astrophysics Data System (ADS)

    Merlo, V.; Salvato, M.; Cirillo, M.; Lucci, M.; Ottaviani, I.; Scherillo, A.; Celentano, G.; Pietropaolo, A.

    2015-03-01

    A neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction, 10B + n → α + 7Li, with α and Li ions generating a hot spot on the current-biased Nb strip which in turn induces a superconducting-normal state transition. The latter is recognized as a voltage signal which is the evidence of the incident neutron. The above described detection principle has been experimentally assessed and verified by irradiating the samples with a pulsed neutron beam at the ISIS spallation neutron source (UK). It is found that the boron coated superconducting strips, kept at a temperature T = 8 K and current-biased below the critical current Ic, are driven into the normal state upon thermal neutron irradiation. As a result of the transition, voltage pulses in excess of 40 mV are measured while the bias current can be properly modulated to bring the strip back to the superconducting state, thus resetting the detector. Measurements on the counting rate of the device are presented and the basic physical features of the detector are discussed.

  2. Decrease of the surface resistance in superconducting niobium resonator cavities by the microwave field

    SciTech Connect

    Ciovati, G. Dhakal, P.; Gurevich, A.

    2014-03-03

    Measurements of the quality factor, Q, of Nb superconducting microwave resonators often show that Q increases by ≃10%–30% with increasing radio-frequency (rf) field, H, up to ∼15–20 mT. Recent high temperature heat treatments can amplify this rf field-induced increase of Q up to ≃50%–100% and extend it to much higher fields ≃100 mT, but the mechanisms of the enhancement of Q(H) remain unclear. Here, we suggest a method to reveal these mechanisms by measuring temperature dependencies of Q at different rf field amplitudes. We show that the increase of Q(H) does not come from a field dependent quasi-particles activation energy or residual resistance, but rather results from the smearing of the density of state by the rf field.

  3. Summary of performance of superconducting radio-frequency cavities built from CBMM niobium ingots

    SciTech Connect

    Ciovati, Gianluigi Dhakal, Pashupati Kneisel, Peter Myneni, Ganapati R.

    2015-12-04

    Several Nb ingots have been provided by CBMM to Jefferson Lab since 2004 as part of an R&D collaboration aimed at evaluating the performance of superconducting radio-frequency cavities built from ingots with different purity, as a results of different ingot production processes. Approximately 32 multi- and single-cell cavities with resonant frequency between ∼1.3-2.3 GHz were built, treated and tested at 2 K at Jefferson Lab between 2004 and 2014. The average peak surface field achieved in cavities made of RRR∼260 and RRR∼100-150 ingots was (119 ± 4) mT and (100 ± 8) mT, respectively. Higher quality factor values at 2.0 K have been measured in medium-purity, compared to higher purity material.

  4. Decrease of the surface resistance in superconducting niobium resonator cavities by the microwave field

    SciTech Connect

    Ciovati, Gianluigi; Dhakal, Pashupati; Gurevich, Alexander V.

    2014-03-03

    Measurements of the quality factor, Q, of Nb superconducting microwave resonators often show that Q increases by {approx_equal} 10%–30% with increasing radio-frequency (rf) field, H, up to {approx} 15-20 mT. Recent high temperature heat treatments can amplify this rf field-induced increase of Q up to {approx_equal} 50%–100% and extend it to much higher fields, but the mechanisms of the enhancement of Q(H) remain unclear. Here, we suggest a method to reveal these mechanisms by measuring temperature dependencies of Q at different rf field amplitudes. We show that the increase of Q(H) does not come from a field dependent quasi-particles activation energy or residual resistance, but rather results from the smearing of the density of state by the rf field.

  5. Niobium-germanium superconducting tapes for high-field magnet applications

    NASA Technical Reports Server (NTRS)

    Braginski, A. I.; Roland, G. W.; Daniel, M. R.; Woolam, J. A.

    1977-01-01

    A process of fabricating superconducting Nb3Ge tapes by chemical vapor deposition (CVD) has been developed and tapes up to 10 meters long fabricated. The typical properties achieved were: critical temperature T sub c = 20 K, upper critical field H sub c2 = 29 tesla at 4.2 K, and J sub c = 3 to 4 x 10 to the 8th power A m(-2) at 4.2 K, 18 tesla. The relative depression of T sub c and H sub c2 compared with the best thin film samples sputtered on sapphire was due to the presence of Nb5Ge3 second-phase particles used as flux pinning centers and to strains induced by thermal mixmatch with Hastelloy B tape substrates. A peculiar field dependence of flux pinning force that was observed in both CVD and sputtered Nb3Ge indicated a premature pin-breaking mechanism or a phase inhomogeneity. Directions of further optimization work were defined.

  6. Measurements of phonon dispersion curves, specific heats, and superconductivity in 4d niobium alloys

    NASA Astrophysics Data System (ADS)

    Cappelletti, R. L.; Wakabayashi, N.; Kamitakahara, W. A.; Traylor, J. G.; Bevolo, A. J.

    1982-05-01

    Inelastic neutron scattering measurements of symmetry-direction phonon dispersion curves at room temperature in two Zr-Nb alloys and in a Zr-Nb-Mo alloy are presented along with their low-temperature specific heats and superconducting transition temperatures. The phenomenological charge-fluctuation model (CFM) is used to fit the curves and to generate the phonon density of states for each sample. Moments of this distribution along with Tc and Nbs(0) are used to determine for comparison with Butler's rigid-muffin-tin calculations. Although numerical agreement is not expected and does not occur, nevertheless the general trend around Nb is reproduced. An analysis of the longitudinal-phonon contribution to λ on the basis of the CFM is presented. Finally the Zr-Nb-Mo alloy is found to behave in detail like a Nb-Mo alloy of the same electron-peratom ratio both in its dispersion curves and in other properties indicating the importance of this parameter.

  7. Proton in SRF Niobium

    SciTech Connect

    Wallace, John Paul

    2011-03-31

    Hydrogen is a difficult impurity to physically deal with in superconducting radio frequency (SRF) niobium, therefore, its properties in the metals should be well understood to allow the metal's superconducting properties to be optimized for minimum loss in the construction of resonant accelerator cavities. It is known that hydrogen is a paramagnetic impurity in niobium from NMR studies. This paramagnetism and its effect on superconducting properties are important to understand. To that end analytical induction measurements aimed at isolating the magnetic properties of hydrogen in SRF niobium are introduced along with optical reflection spectroscopy which is also sensitive to the presence of hydrogen. From the variety, magnitude and rapid kinetics found in the optical and magnetic properties of niobium contaminated with hydrogen forced a search for an atomic model. This yielded quantum mechanical description that correctly generates the activation energy for diffusion of the proton and its isotopes not only in niobium but the remaining metals for which data is available. This interpretation provides a frame work for understanding the individual and collective behavior of protons in metals.

  8. Proton in SRF Niobium

    NASA Astrophysics Data System (ADS)

    Wallace, John Paul

    2011-03-01

    Hydrogen is a difficult impurity to physically deal with in superconducting radio frequency (SRF) niobium, therefore, its properties in the metals should be well understood to allow the metal's superconducting properties to be optimized for minimum loss in the construction of resonant accelerator cavities. It is known that hydrogen is a paramagnetic impurity in niobium from NMR studies. This paramagnetism and its effect on superconducting properties are important to understand. To that end analytical induction measurements aimed at isolating the magnetic properties of hydrogen in SRF niobium are introduced along with optical reflection spectroscopy which is also sensitive to the presence of hydrogen. From the variety, magnitude and rapid kinetics found in the optical and magnetic properties of niobium contaminated with hydrogen forced a search for an atomic model. This yielded quantum mechanical description that correctly generates the activation energy for diffusion of the proton and its isotopes not only in niobium but the remaining metals for which data is available. This interpretation provides a frame work for understanding the individual and collective behavior of protons in metals.

  9. A-15 Superconducting composite wires and a method for making

    DOEpatents

    Suenaga, Masaki; Klamut, Carl J.; Luhman, Thomas S.

    1984-01-01

    A method for fabricating superconducting wires wherein a billet of copper containing filaments of niobium or vanadium is rolled to form a strip which is wrapped about a tin-alloy core to form a composite. The alloy is a tin-copper alloy for niobium filaments and a gallium-copper alloy for vanadium filaments. The composite is then drawn down to a desired wire size and heat treated. During the heat treatment process, the tin in the bronze reacts with the niobium to form the superconductor niobium tin. In the case where vanadium is used, the gallium in the gallium bronze reacts with the vanadium to form the superconductor vanadium gallium. This new process eliminates the costly annealing steps, external tin plating and drilling of bronze ingots required in a number of prior art processes.

  10. Wrapping process for fabrication of A-15 superconducting composite wires

    DOEpatents

    Suenaga, M.; Klamut, C.J.; Luhman, T.S.

    1980-08-15

    A method for fabricating superconducting wires wherein a billet of copper containing filaments of niobium or vanadium is rolled to form a strip which is wrapped about a tin-alloy core to form a composite. The alloy is a tin-copper alloy for niobium filaments and a gallium-copper alloy for vanadium filaments. The composite is then drawn down to a desired wire size and heat treated. During the heat treatment process, the tin in the bronze reacts with the niobium to form the superconductor niobium tin. In the case where vanadium is used, the gallium in the gallium bronze reacts with the vanadium to form the superconductor vanadium gallium. This new process eliminates the costly annealing steps, external tin plating and drilling of bronze ingots required in a number of prior art processes.

  11. Direct observation of the current distribution in thin superconducting strips using magneto-optic imaging

    NASA Astrophysics Data System (ADS)

    Johansen, T. H.; Baziljevich, M.; Bratsberg, H.; Galperin, Y.; Lindelof, P. E.; Shen, Y.; Vase, P.

    1996-12-01

    Magneto-optic imaging was used for a detailed study of the flux and current distribution of a long thin strip of YBa2Cu3O7-δ placed in a perpendicular external magnetic field. The inverse magnetic problem, i.e., that of deriving from a field map the underlying current distribution, is formulated and solved for the strip geometry. Applying the inversion to the magneto-optically found field map we find on a model-independent basis the current distribution across the strip to be in remarkable agreement with the profile predicted by the Bean model. The paper also presents results on the behavior of the Bi-doped YIG film with in-plane anisotropy which we use as field indicator, explaining why previous measurements of flux density profiles have displayed surprisingly large deviations from the expected behavior.

  12. Introduction to Ingot Niobium

    SciTech Connect

    Ganapati Rao Mynen, Andrew Hutton

    2011-03-01

    Superconducting radiofrequency (SRF) technology using niobium accelerating cavities was first applied at large scale in the recirculating electron linear accelerator CEBAF—the Continuous Electron Beam Accelerator Facility in Newport News, Virginia, USA, at what is now called Thomas Jefferson National Accelerator Facility, or Jefferson Lab. Building on the high quality factors and peak magnetic fields found in low residual resistivity ratio (low-RRR) solid niobium in the 1970s, Jefferson Lab has reintroduced ingot niobium technology. High tantalum content in ingot niobium is not expected to negatively impact cavity performance, but will reduce the cost of accelerator structures considerably. Optimized low-cost CW linear accelerators built with ingot niobium will show the way for future R&D and industrial applications. This paper portrays the Jefferson Lab SRF context, reviews the early history of ingot niobium technology from over a third of a century ago, explains the technical advantages of that technology's recent reintroduction, and presents the outlook for further development.

  13. Introduction to Ingot Niobium

    SciTech Connect

    Myneni, Ganapati Rao; Hutton, Andrew

    2011-03-31

    Superconducting radiofrequency (SRF) technology using niobium accelerating cavities was first applied at large scale in the recirculating electron linear accelerator CEBAF--the Continuous Electron Beam Accelerator Facility in Newport News, Virginia, USA, at what is now called Thomas Jefferson National Accelerator Facility, or Jefferson Lab. Building on the high quality factors and peak magnetic fields found in low residual resistivity ratio (low-RRR) solid niobium in the 1970s, Jefferson Lab has reintroduced ingot niobium technology. High tantalum content in ingot niobium is not expected to negatively impact cavity performance, but will reduce the cost of accelerator structures considerably. Optimized low-cost CW linear accelerators built with ingot niobium will show the way for future R and D and industrial applications. This paper portrays the Jefferson Lab SRF context, reviews the early history of ingot niobium technology from over a third of a century ago, explains the technical advantages of that technology's recent reintroduction, and presents the outlook for further development.

  14. Niobium Production at Tokyo Denkai

    SciTech Connect

    Umezawa, Hiroaki

    2011-03-31

    In recent years, single-crystal/large-grain niobium has received much attention. It has the following advantages: rolling-annealing is unnecessary, and superconducting cavities made from large-grain niobium discs may not require electropolishing. However, to obtain a large-grain disc, an ingot must be sliced using a saw and finished smooth by using a lathe. Slicing a disc takes several hours and produces niobium shavings. KEK, Tokyo Denkai, and TKX Corporation have developed a new niobium ingot slicing technique, and Tokyo Denkai has installed the slicing machine. This study describes the new ingot slicing technology, which ensures state-of-the-art productivity for the superconducting radio frequency (SRF) cavity material industry.

  15. Effect of Electropolishing and Low-Temperature Baking on the Superconducting Properties of Large-Grain Niobium

    SciTech Connect

    A. S. Dhavale, G. Ciovati, G. R. Myneni

    2011-03-01

    Measurements of superconducting properties such as bulk and surface critical fields and thermal conductivity have been carried out in the temperature range from 2 K to 8 K on large-grain samples of different purity and on a high-purity fine-grain sample, for comparison. The samples were treated by electropolishing and low temperature baking (120° C, 48 h). While the residual resistivity ratio changed by a factor of ~3 among the samples, no significant variation was found in their superconducting properties. The onset field for flux penetration at 2 K, Hffp, measured within a ~30 µm depth from the surface, was ~160 mT, close to the bulk value. The baking effect was mainly to increase the field range up to which a coherent superconducting phase persists on the surface, above the upper critical field.

  16. Production of High Purity Niobium Ingots at CBMM

    SciTech Connect

    Moura, Lourenco de; Faria Sousa, Clovis Antonio de; Burgos Cruz, Edmundo

    2011-03-31

    CBMM is a fully integrated company, from the mine to the end line of the production chain, supplying different niobium products to the world market: ferroniobium, nickelniobium, niobium pentoxide and high purity metallic niobium. This high purity metallic niobium has long been known to exhibit superconductivity below 9.25 Kelvin. This characteristic has the potential to bring technological benefits for many different areas such as medicine, computing and environment. This paper presents the raw material requirements as well as CBMM experience on producing high purity niobium ingots. The results prove that CBMM material can be the best solution for special applications such as low cost superconductive radiofrequency cavities.

  17. Tests of the radiation hardness of VLSI Integrated Circuits and Silicon Strip Detectors for the SSC (Superconducting Super Collider) under neutron, proton, and gamma irradiation

    SciTech Connect

    Ziock, H.J.; Milner, C.; Sommer, W.F. ); Carteglia, N.; DeWitt, J.; Dorfan, D.; Hubbard, B.; Leslie, J.; O'Shaughnessy, K.F.; Pitzl, D.; Rowe, W.A.; Sadrozinski, H.F.W.; Seiden, A.; Spencer, E. . Inst. for Particle Physics); Ellison, J.A. ); Ferguson, P. ); Giubellino

    1990-01-01

    As part of a program to develop a silicon strip central tracking detector system for the Superconducting Super Collider (SSC) we are studying the effects of radiation damage in silicon detectors and their associated front-end readout electronics. We report on the results of neutron and proton irradiations at the Los Alamos National Laboratory (LANL) and {gamma}-ray irradiations at UC Santa Cruz (UCSC). Individual components on single-sided AC-coupled silicon strip detectors and on test structures were tested. Circuits fabricated in a radiation hard CMOS process and individual transistors fabricated using dielectric isolation bipolar technology were also studied. Results indicate that a silicon strip tracking detector system should have a lifetime of at least one decade at the SSC. 17 refs., 17 figs.

  18. The guidance of kinematic vortices in a mesoscopic superconducting strip with artificial defects

    NASA Astrophysics Data System (ADS)

    He, An; Xue, Cun; Yong, Huadong; Zhou, Youhe

    2016-06-01

    Within the time-dependent Ginzburg–Landau (TDGL) theory, we theoretically investigated the dynamic properties of vortex–antivortex (V–Av) pairs in a current-carrying superconductor strip with one tilted slit or two transversely/longtitudinally arranged slits in the presence of a weak magnetic field. The effect of the rotation angle on the resistive state in the sample with one tilted slit was considered. The location of phase slippage in the sample can be predetermined by the rotation angle of the tilted slit. We found the coalescence of the phase-slip lines (PSLs) during a periodic multiharmonic voltage oscillation. This leads to two stages of voltage oscillation at zero applied field and three stages at weak magnetic field since the coalescence of left and right PSLs are staggered in the latter case. Moreover, the influence of relative position and size of the two slits on the transport properties of the sample are also studied. The dynamic behavior of V–Av pairs depends on not only the slit length but also their horizontal or vertical interval distance between the two slits. Since the geometry of sample has an important influence on the distribution of supercurrent across the sample, we demonstrate the possibility to efficiently guide the kinematic vortices by adjusting the relevant parameters.

  19. Increased Superconducting Transition Temperature of a Niobium Thin Film Proximity Coupled to Gold Nanoparticles Using Linking Organic Molecules

    NASA Astrophysics Data System (ADS)

    Katzir, Eran; Yochelis, Shira; Zeides, Felix; Katz, Nadav; Kalcheim, Yaov; Millo, Oded; Leitus, Gregory; Myasodeyov, Yuri; Shapiro, Boris Ya.; Naaman, Ron; Paltiel, Yossi

    2012-03-01

    The superconducting critical temperature, TC, of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The TC increases by up to 10% for certain linker length and NP size. No change is observed when the nanoparticles are physisorbed with nonlinking molecules. Electron tunneling spectra acquired on the linked NPs below TC typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers.

  20. Increased superconducting transition temperature of a niobium thin film proximity coupled to gold nanoparticles using linking organic molecules.

    PubMed

    Katzir, Eran; Yochelis, Shira; Zeides, Felix; Katz, Nadav; Kalcheim, Yaov; Millo, Oded; Leitus, Gregory; Myasodeyov, Yuri; Shapiro, Boris Ya; Naaman, Ron; Paltiel, Yossi

    2012-03-01

    The superconducting critical temperature, T(C), of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The T(C) increases by up to 10% for certain linker length and NP size. No change is observed when the nanoparticles are physisorbed with nonlinking molecules. Electron tunneling spectra acquired on the linked NPs below T(C) typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers. PMID:22463444

  1. Probing the fundamental limit of niobium in high radiofrequency fields by dual mode excitation in superconducting radiofrequency cavities

    SciTech Connect

    Eremeev, Grigory; Geng, Rongli; Palczewski, Ari

    2011-07-01

    We have studied thermal breakdown in several multicell superconducting radiofrequency cavity by simultaneous excitation of two TM{sub 010} passband modes. Unlike measurements done in the past, which indicated a clear thermal nature of the breakdown, our measurements present a more complex picture with interplay of both thermal and magnetic effects. JLab LG-1 that we studied was limited at 40.5 MV/m, corresponding to B{sub peak} = 173 mT, in 8{pi}/9 mode. Dual mode measurements on this quench indicate that this quench is not purely magnetic, and so we conclude that this field is not the fundamental limit in SRF cavities.

  2. Modulation of superconducting critical temperature in niobium film by using all-solid-state electric-double-layer transistor

    SciTech Connect

    Tsuchiya, Takashi E-mail: TERABE.Kazuya@nims.go.jp; Moriyama, Satoshi; Terabe, Kazuya E-mail: TERABE.Kazuya@nims.go.jp; Aono, Masakazu

    2015-07-06

    An all-solid-state electric-double-layer transistor (EDLT) was fabricated for electrical modulation of the superconducting critical temperature (T{sub c}) of Nb film epitaxially grown on α-Al{sub 2}O{sub 3} (0001) single crystal. In an experiment, T{sub c} was modulated from 8.33 to 8.39 K while the gate voltage (V{sub G}) was varied from 2.5 to −2.5 V. The specific difference of T{sub c} for the applied V{sub G} was 12 mK/V, which is larger than that of an EDLT composed of ionic liquid. A T{sub c} enhancement of 300 mK was found at the Li{sub 4}SiO{sub 4}/Nb film interface and is attributed to an increase in density of states near the Fermi level due to lattice constant modulation. This solid electrolyte gating method should enable development of practical superconducting devices highly compatible with other electronic devices.

  3. Superconductivity

    SciTech Connect

    Langone, J.

    1989-01-01

    This book explains the theoretical background of superconductivity. Includes discussion of electricity, material fabrication, maglev trains, the superconducting supercollider, and Japanese-US competition. The authors reports the latest discoveries.

  4. Effect of nearby Pearl vortices upon the Ic versus B characteristics of planar Josephson junctions in thin and narrow superconducting strips

    SciTech Connect

    Clem, John R.

    2011-10-03

    In this paper I show how to calculate the effect of a nearby Pearl vortex or antivortex upon the critical current I{sub c}(B) when a perpendicular magnetic induction B is applied to a planar Josephson junction in a long, thin, superconducting strip of width W much less than the Pearl length {Lambda} = 2{lambda}2/d, where {lambda} is the London penetration depth and d is the thickness (d < {lambda}). The theoretical results provide a qualitative explanation of unusual features recently observed experimentally by Golod et al. [ Phys. Rev. Lett. 104 227003 (2010)] in a device with a similar geometry.

  5. The design and evaluation of superconducting connectors

    NASA Technical Reports Server (NTRS)

    Payne, J. E.

    1982-01-01

    The development of a superconducting connector for superconducting circuits on space flights is described. It is proposed that such connectors be used between the superconducting readout loop and the SQUID magnetometer in the Gravity Probe B experiment. Two types of connectors were developed. One type employs gold plated niobium wires making pressure connections to gold plated niobium pads. Lead-plated beryllium-copper spring contacts can replace the niobium wires. The other type is a rigid solder or weld connection between the niobium wires and the niobium pads. A description of the methods used to produce these connectors is given and their performance analyzed.

  6. Tunable superconducting microstrip resonators

    NASA Astrophysics Data System (ADS)

    Adamyan, A. A.; Kubatkin, S. E.; Danilov, A. V.

    2016-04-01

    We report on a simple yet versatile design for a tunable superconducting microstrip resonator. Niobium nitride is employed as the superconducting material and aluminum oxide, produced by atomic layer deposition, as the dielectric layer. We show that the high quality of the dielectric material allows to reach the internal quality factors in the order of Qi˜104 in the single photon regime. Qi rapidly increases with the number of photons in the resonator N and exceeds 105 for N ˜10 -50 . A straightforward modification of the basic microstrip design allows to pass a current bias through the strip and to control its kinetic inductance. We achieve a frequency tuning δf =62 MHz around f0=2.4 GHz for a fundamental mode and δf =164 MHz for a third harmonic. This translates into a tuning parameter Qiδf /f0=150 . The presented design can be incorporated into essentially any superconducting circuitry operating at temperatures below 2.5 K.

  7. Vortex trapping and expulsion in thin-film YBa2Cu3O7-δ strips

    NASA Astrophysics Data System (ADS)

    Kuit, K. H.; Kirtley, J. R.; van der Veur, W.; Molenaar, C. G.; Roesthuis, F. J. G.; Troeman, A. G. P.; Clem, J. R.; Hilgenkamp, H.; Rogalla, H.; Flokstra, J.

    2008-04-01

    A scanning superconducting quantum interference device microscope was used to image vortex trapping as a function of the magnetic induction during cooling in thin-film YBa2Cu3O7-δ (YBCO) strips for strip widths W from 2 to 50μm . We found that vortices were excluded from the strips when the induction Ba was below a critical induction Bc . We present a simple model for the vortex exclusion process which takes into account the vortex-antivortex pair production energy as well as the vortex Meissner and self-energies. This model predicts that the real density n of trapped vortices is given by n=(Ba-BK)/Φ0 with BK=1.65Φ0/W2 and Φ0=h/2e the superconducting flux quantum. This prediction is in good agreement with our experiments on YBCO, as well as with previous experiments on thin-film strips of niobium. We also report on the positions of the trapped vortices. We found that at low densities the vortices were trapped in a single row near the centers of the strips, with the relative intervortex spacing distribution width decreasing as the vortex density increased, a sign of longitudinal ordering. The critical induction for two rows forming in the 35μm wide strip was (2.89+1.91-0.93)Bc , consistent with a numerical prediction.

  8. Superconductivity

    NASA Astrophysics Data System (ADS)

    Yeo, Yung K.

    Many potential high-temperature superconductivity (HTS) military applications have been demonstrated by low-temperature superconductivity systems; they encompass high efficiency electric drives for naval vessels, airborne electric generators, energy storage systems for directed-energy weapons, electromechanical launchers, magnetic and electromagnetic shields, and cavity resonators for microwave and mm-wave generation. Further HST applications in militarily relevant fields include EM sensors, IR focal plane arrays, SQUIDs, magnetic gradiometers, high-power sonar sources, and superconducting antennas and inertial navigation systems. The development of SQUID sensors will furnish novel magnetic anomaly detection methods for ASW.

  9. Ingot Niobium RF Cavity Design and Development at BARC

    SciTech Connect

    Mittal, K. C.; Mondal, J.; Ghatak, S.; Dhavale, A. S.; Ghodke, S. R.; Vohra, R. S.; Jawale, S. B.; Dutta, D.; Pujari, P. K.; Saha, T. K.; Bapat, A. V.

    2011-03-31

    This article presents the different activity of Ingot niobium in BARC. BARC is developing a technology for the accelerator driven subcritical system (ADSS) that will be mainly utilized for the transmutation of nuclear waste and enrichment of U{sup 233}. Design and development of superconducting medium velocity cavity has been taken up as a part of the ADSS project. The design and fabrication of f = 1050 MHz, {beta} = 0.49 with Ingot niobium will be presented. Positron annihilation studies are conducted on small samples of ingot niobium to understand the defect depth profile of the niobium surface. The results are presented here.

  10. Superconductivity:

    NASA Astrophysics Data System (ADS)

    Sacchetti, N.

    In this paper a short historical account of the discovery of superconductivity and of its gradual development is given. The physical interpretation of its various aspects took about forty years (from 1911 to 1957) to reach a successful description of this phenomenon in terms of a microscopic theory At the very end it seemed that more or less everything could be reasonably interpreted even if modifications and refinements of the original theory were necessary. In 1986 the situation changed abruptly when a cautious but revolutionary paper appeared showing that superconductivity was found in certain ceramic oxides at temperatures above those up to then known. A rush of frantic experimental activity started world-wide and in less than one year it was shown that superconductivity is a much more widespread phenomenon than deemed before and can be found at temperatures well above the liquid air boiling point. The complexity and the number of the substances (mainly ceramic oxides) involved call for a sort of modern alchemy if compounds with the best superconducting properties are to be manufactured. We don't use the word alchemy in a deprecatory sense but just to emphasise that till now nobody can say why these compounds are what they are: superconductors.

  11. Nb-Pb Superconducting RF Gun

    SciTech Connect

    Sekutowicz, J.; Iversen, J.; Kreps, G.; Moller, W.D.; Singer, W.; Singer, X.; Ben-Zvi, I.; Burrill, A.; Smedley, J.; Rao, T.; Ferrario, M.; Kneisel, P.; Langner, J.; Strzyzewski, P.; Lefferts, R.; Lipski, A.; Szalowski, K.; Ko, K.; Xiao, L.; /SLAC

    2006-03-29

    We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.

  12. Nb-Pb superconducting RF gun

    SciTech Connect

    J. Sekutowicz; J. Iversen; G. Kreps; W.D. Moller; W. Singer; X. Singer; I. Ben-Zvi; A. Burrill; J. Smedley; T. Rao; M. Ferrario; P. Kneisel; J. Langner; P. Strzyzewski; R. Lefferts; A. Lipski; K. Szalowski; K. Ko; L. Xiao

    2006-04-14

    We report on the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead, as compared to other superconducting metals. The concept, mentioned in a previous paper, follows the attractive approach of all niobium superconducting RF-gun as it has been proposed by the BNL group. Measured values of quantum efficiency for lead at various photon energies, analysis of recombination time of photon-broken Cooper pairs for lead and niobium, and preliminary cold test results are discussed in this paper.

  13. Demonstration of single-flux-quantum readout circuits for time-of-flight mass spectrometry systems using superconducting strip ion detectors

    NASA Astrophysics Data System (ADS)

    Sano, Kyosuke; Takahashi, Yoshihiro; Yamanashi, Yuki; Yoshikawa, Nobuyuki; Zen, Nobuyuki; Ohkubo, Masataka

    2015-07-01

    We have been developing a superconducting time-of-flight mass spectrometry (TOF-MS) system that consists of a superconducting strip ion detector (SSID) and a single-flux-quantum (SFQ) time-to-digital converter. In this study, we implement a prototype TOF-MS system using an SSID and an SFQ readout circuit in which output signals from the SSID are read out by the SFQ readout circuit and output to room-temperature electronics. The SFQ readout circuit, which consists of a current discriminator, a Josephson transmission line and an SFQ/dc converter, was fabricated using the AIST Nb standard process (STP2), and installed in a 4.2 K cryostat with a meander-shaped NbN SSID measuring 200 μm square. The dark count rate for the SSID was measured as increasing exponentially with the increase in the bias current of the SSID by using the SFQ readout circuit. Mass spectrum measurements of biomolecules, Angiotensin I, which has a molecular weight of 1296 Da, were demonstrated by using the matrix-assisted laser desorption/ionization method, and a clear corresponding peak was observed in the mass spectrum.

  14. Effect of hydrogen on surface of niobium

    SciTech Connect

    Gadgil, V.J.; Keim, E.G.

    1998-12-31

    Niobium single crystals are used as substrate material for constructing superconducting quantum interference device of SQUID. The use of niobium is prompted by the fact that it is a low {Tc} metallic superconductor. In order to fabricate the device the surface of the crystal has to be polished flat. This is achieved by combination of mechanical polishing and electrochemical polishing. It has been reported that during electrochemical polishing hydrogen can enter the material forming Niobium hydrides. These can result in surface roughening of a magnitude greater than the thickness of the films subsequently deposited. This leads to failure of the films. The problem can be solved by annealing the material at 300 C to remove any hydrogen that might be present. However it is phenomenologically interesting to study the effect of electrochemical hydrogen charging on the surface of Niobium.

  15. Local structure around the flux pinning centers in superconducting niobium silicon oxynitride (Nb{sub 0.87}Si{sub 0.09}□{sub 0.04})(N{sub 0.87}O{sub 0.13})

    SciTech Connect

    Ohashi, Y.; Masubuchi, Y.; Venkateshwarlu, D.; Ganesan, V.; Yakhmi, J.V.; Yoshida, T.; Kikkawa, S.

    2014-02-15

    The superconducting transition temperature of niobium silicon oxynitride (Nb{sub 0.87}Si{sub 0.09}□{sub 0.04})(N{sub 0.87}O{sub 0.13}) exhibits a gradual reduction from 16.8 K to around 11 K under an increasing applied magnetic field of up to 14 T. This relatively small T{sub c} reduction under an applied magnetic field suggests a robustness of its superconducting behavior in comparison to that in the parent niobium oxynitride. It was similar to the flux pinning effect observed in the large magnetic hysteresis of the niobium-silicon oxynitrides in our previous study. Both Si K-edge XANES and {sup 29}Si MAS-NMR indicated that the local structure of pinning centers around the silicon atoms close to cationic vacancies was similar to that of Si in amorphous SiO{sub 2} in the rock-salt structure of niobium oxynitride. - Graphical abstract: Potential energy scan of the Si atom in the most stable Si{sub 3}□O{sub 3}N cube around the vacancy in our preliminary simulation on niobium silicon oxynitride (Nb{sub 0.87}Si{sub 0.09}□{sub 0.04})(N{sub 0.87}O{sub 0.13}). A possible distortion of the Si atom was suggested from its octahedral towards tetrahedral position forming the local structure similar to that in amorphous SiO{sub 2}. Display Omitted - Highlights: • Critical current density was enhanced in superconducting niobium oxynitride. • The robustness was introduced by forming rock-salt type niobium silicon oxynitride. • The silicon atom had a local structure similar to that in amorphous SiO{sub 2} in the rock-salt type lattice. • The local structure was formed together with its neighboring cationic vacancy. • It contributed as the flux pinning center in the NbSiNO.

  16. Study of AC/RF properties of SRF ingot niobium

    SciTech Connect

    Dhakal, Pashupati; Tsindlekht, Menachem I; Genkin, Valery M; Ciovati, Gianluigi; Myneni, Ganapati Rao

    2013-09-01

    In an attempt to correlate the performance of superconducting radiofrequency cavities made of niobium with the superconducting properties, we present the results of the magnetization and ac susceptibility of the niobium used in the superconducting radiofrequency cavity fabrication. The samples were subjected to buffer chemical polishing (BCP) surface and high temperature heat treatments, typically applied to the cavities fabrications. The analysis of the results show the different surface and bulk ac conductivity for the samples subjected to BCP and heat treatment. Furthermore, the RF surface impedance is measured on the sample using a TE011 microwave cavity for a comparison to the low frequency measurements.

  17. Process for recovering niobium from uranium-niobium alloys

    DOEpatents

    Wallace, Steven A.; Creech, Edward T.; Northcutt, Walter G.

    1983-01-01

    Niobium is recovered from scrap uranium-niobium alloy by melting the scrap with tin, solidifying the billet thus formed, heating the billet to combine niobium with tin therein, placing the billet in hydrochloric acid to dissolve the uranium and leave an insoluble residue of niobium stannide, then separating the niobium stannide from the acid.

  18. Process for recovering niobium from uranium-niobium alloys

    SciTech Connect

    Wallace, S.A.; Creech, E.T.; Northcutt, W.G.

    1983-11-01

    Niobium is recovered from scrap uranium-niobium alloy by melting the scrap with tin, solidifying the billet thus formed, heating the billet to combine niobium with tin therein, placing the billet in hydrochloric acid to dissolve the uranium and leave an insoluble residue of niobium stannide, then separating the niobium stannide from the acid.

  19. Precipitation of hydrides in high purity niobium after different treatments

    SciTech Connect

    Barkov, F.; Romanenko, A.; Trenikhina, Y.; Grassellino, A.

    2013-01-01

    Precipitation of lossy non-superconducting niobium hydrides represents a known problem for high purity niobium in superconducting applications. Using cryogenic optical and laser confocal scanning microscopy we have directly observed surface precipitation and evolution of niobium hydrides in samples after different treatments used for superconducting RF cavities for particle acceleration. Precipitation is shown to occur throughout the sample volume, and the growth of hydrides is well described by the fast diffusion-controlled process in which almost all hydrogen is precipitated at $T=140$~K within $\\sim30$~min. 120$^{\\circ}$C baking and mechanical deformation are found to affect hydride precipitation through their influence on the number of nucleation and trapping centers.

  20. PURE NIOBIUM AS A PRESSURE VESSEL MATERIAL

    SciTech Connect

    Peterson, T. J.; Carter, H. F.; Foley, M. H.; Klebaner, A. L.; Nicol, T. H.; Page, T. M.; Theilacker, J. C.; Wands, R. H.; Wong-Squires, M. L.; Wu, G.

    2010-04-09

    Physics laboratories around the world are developing niobium superconducting radio frequency (SRF) cavities for use in particle accelerators. These SRF cavities are typically cooled to low temperatures by direct contact with a liquid helium bath, resulting in at least part of the helium container being made from pure niobium. In the U.S., the Code of Federal Regulations allows national laboratories to follow national consensus pressure vessel rules or use of alternative rules which provide a level of safety greater than or equal to that afforded by ASME Boiler and Pressure Vessel Code. Thus, while used for its superconducting properties, niobium ends up also being treated as a material for pressure vessels. This report summarizes what we have learned about the use of niobium as a pressure vessel material, with a focus on issues for compliance with pressure vessel codes. We present results of a literature search for mechanical properties and tests results, as well as a review of ASME pressure vessel code requirements and issues.

  1. Pure Niobium as a Pressure Vessel Material

    NASA Astrophysics Data System (ADS)

    Peterson, T. J.; Carter, H. F.; Foley, M. H.; Klebaner, A. L.; Nicol, T. H.; Page, T. M.; Theilacker, J. C.; Wands, R. H.; Wong-Squires, M. L.; Wu, G.

    2010-04-01

    Physics laboratories around the world are developing niobium superconducting radio frequency (SRF) cavities for use in particle accelerators. These SRF cavities are typically cooled to low temperatures by direct contact with a liquid helium bath, resulting in at least part of the helium container being made from pure niobium. In the U.S., the Code of Federal Regulations allows national laboratories to follow national consensus pressure vessel rules or use of alternative rules which provide a level of safety greater than or equal to that afforded by ASME Boiler and Pressure Vessel Code. Thus, while used for its superconducting properties, niobium ends up also being treated as a material for pressure vessels. This report summarizes what we have learned about the use of niobium as a pressure vessel material, with a focus on issues for compliance with pressure vessel codes. We present results of a literature search for mechanical properties and tests results, as well as a review of ASME pressure vessel code requirements and issues.

  2. Variation of Mechanical Properties of High RRR And Reactor Grade Niobium With Heat Treatments

    SciTech Connect

    Ganapati Myneni; H. Umezawa

    2003-06-01

    Superconducting rf cavities used as accelerating structures in particle accelerators are made from high purity niobium with residual resistance ratios greater than 250. Reactor grade niobium is also used to make wave-guide and/or end group components for these accelerating structures. The major impurities in this type of niobium are interstitially dissolved gases such as hydrogen, nitrogen, and oxygen in addition to carbon. After fabricating the niobium accelerating structures, they are subjected to heat treatments for several hours in vacuum at temperatures of up to 900 C for degassing hydrogen or up to 1400 C for improving the thermal conductivity of niobium considerably. These heat treatments are affecting the mechanical properties of niobium drastically. In this paper the variation of the mechanical properties of high purity and reactor grade niobium with heat treatments in a vacuum of {approx} 10{sup -6} Torr and temperatures from 600 C to 1250 C for periods of 10 to 6 hours are presented.

  3. Determination of bulk and surface superconducting properties of N2-doped cold worked, heat treated and electro-polished SRF grade niobium

    SciTech Connect

    Chetri, Santosh; Larbalestier, David C.; Lee, Peter J.; Dhakal, Pashupati; Sung, Zu -Hawn

    2015-12-01

    In this study, nitrogen-doped cavities show significant performance improvement in the medium accelerating field regime due to a lowered RF surface resistivity. However, the mechanism of enhancement has not been clearly explained. Our experiments explore how N2-doping influences Nb bulk and surface superconducting properties, and compare the N2-doped properties with those obtained previously with conventionally treated samples. High purity Nb-rod was mechanically deformed and post treated based on a typical SRF cavity treatment recipe. The onset of flux penetration at Hc1, and the upper and the surface critical fields, Hc2 and Hc3, were characterized by magnetic hysteresis and AC susceptibility techniques. The surface depth profile responsible for superconductivity was examined by changing AC amplitude in AC susceptibility, and the microstructure was directly observed with EBSD-OIM. We are also investigating surface chemistry for detailed composition using XPS. We have found that N2-doping at 800 °C significantly reduces the Hc3/Hc2 ratio towards the ideal value of ~1.7, and conclude that AC susceptibility is capable of following changes to the surface properties induced by N2-doping.

  4. Determination of bulk and surface superconducting properties of N2-doped cold worked, heat treated and electro-polished SRF grade niobium

    DOE PAGESBeta

    Chetri, Santosh; Larbalestier, David C.; Lee, Peter J.; Dhakal, Pashupati; Sung, Zu -Hawn

    2015-12-01

    In this study, nitrogen-doped cavities show significant performance improvement in the medium accelerating field regime due to a lowered RF surface resistivity. However, the mechanism of enhancement has not been clearly explained. Our experiments explore how N2-doping influences Nb bulk and surface superconducting properties, and compare the N2-doped properties with those obtained previously with conventionally treated samples. High purity Nb-rod was mechanically deformed and post treated based on a typical SRF cavity treatment recipe. The onset of flux penetration at Hc1, and the upper and the surface critical fields, Hc2 and Hc3, were characterized by magnetic hysteresis and AC susceptibilitymore » techniques. The surface depth profile responsible for superconductivity was examined by changing AC amplitude in AC susceptibility, and the microstructure was directly observed with EBSD-OIM. We are also investigating surface chemistry for detailed composition using XPS. We have found that N2-doping at 800 °C significantly reduces the Hc3/Hc2 ratio towards the ideal value of ~1.7, and conclude that AC susceptibility is capable of following changes to the surface properties induced by N2-doping.« less

  5. Superconducting transmission line particle detector

    DOEpatents

    Gray, Kenneth E.

    1989-01-01

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non-superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propogating in a superconducting transmission line are used to resolve N.sup.2 ambiguity of charged particle events.

  6. Superconducting transmission line particle detector

    DOEpatents

    Gray, K.E.

    1988-07-28

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non- superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propagating in a superconducting transmission line are used to resolve N/sup 2/ ambiguity of charged particle events. 6 figs.

  7. On the reliable determination of the magnetic field for first flux-line penetration in technical niobium material

    SciTech Connect

    Ganapati Rao Myneni

    2007-09-05

    We present a way to reliably determine the field for first penetration H$_P$ in various kinds of bulk samples of niobium material used in the technical applications like fabrication of superconducting RF-cavities. Special attention is given to the role of flux line pinning in the determination of H$_P$. It is observed that the pinning properties and H$_P$ can change (or can be altered) significantly with the chemical treatment of bulk niobium. A correlation is proposed between H$_P$ of the niobium materials and the anomalous high-field Q-drop observed in the superconducting RF-cavities fabricated using such niobium material.

  8. Quench-age method for the fabrication of niobium-aluminum superconductors

    DOEpatents

    Pickus, Milton R.; Ciardella, Robert L.

    1978-01-01

    A flexible Nb.sub.3 Al superconducting wire is fabricated from a niobium-aluminum composite wire by heating to form a solid solution which is retained at room temperature as a metastable solid solution by quenching. The metastable solid solution is then transformed to the stable superconducting A-15 phase by low temperature aging. The transformation induced by aging can be controlled to yield either a multifilamentary or a solid A-15 core surrounded by ductile niobium.

  9. Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity

    SciTech Connect

    Dhakal, P.; Ciovati, G.; Myneni, G. R.; Gray, K. E.; Groll, N.; Maheshwari, P.; McRae, D. M.; Pike, R.; Proslier, T.; Stevie, F.; Walsh, R. P.; Yang, Q.; Zasadzinzki, J.

    2013-04-01

    Large-grain Nb has become a viable alternative to fine-grain Nb for the fabrication of superconducting radio-frequency cavities. In this contribution we report the results from a heat treatment study of a large-grain 1.5 GHz single-cell cavity made of “medium purity” Nb. The baseline surface preparation prior to heat treatment consisted of standard buffered chemical polishing. The heat treatment in the range 800–1400°C was done in a newly designed vacuum induction furnace. Q{sub 0} values of the order of 2×10{sup 10} at 2.0 K and peak surface magnetic field (B{sub p}) of 90 mT were achieved reproducibly. A Q{sub 0} value of (5±1)×10{sup 10} at 2.0 K and B{sub p}=90mT was obtained after heat treatment at 1400°C. This is the highest value ever reported at this temperature, frequency, and field. Samples heat treated with the cavity at 1400°C were analyzed by secondary ion mass spectrometry, x-ray photoelectron spectroscopy, energy dispersive x ray, point-contact tunneling, and x-ray diffraction, and revealed a complex surface composition which includes titanium oxide, increased carbon, and nitrogen content but reduced hydrogen concentration compared to a non-heat-treated sample.

  10. Process for recovering niobium from uranium-niobium alloys

    DOEpatents

    Wallace, S.A.; Creech, E.T.; Northcutt, W.G.

    1982-09-27

    Niobium is recovered from scrap uranium-niobium alloy by melting the scrap with tin, solidifying the billet thus formed, heating the billet to combine niobium with tin therein, placing the billet in hydrochloric acid to dissolve the uranium and form a precipitate of niobium stannide, then separating the precipitate from the acid.

  11. Buffered Electrochemical Polishing of Niobium

    SciTech Connect

    Gianluigi Ciovati; Tian, Hui; Corcoran, Sean

    2011-03-01

    The standard preparation of superconducting radio-frequency (SRF) cavities made of pure niobium include the removal of a 'damaged' surface layer, by buffered chemical polishing (BCP) or electropolishing (EP), after the cavities are formed. The performance of the cavities is characterized by a sharp degradation of the quality factor when the surface magnetic field exceeds about 90 mT, a phenomenon referred to as 'Q-drop.' In cavities made of polycrystalline fine grain (ASTM 5) niobium, the Q-drop can be significantly reduced by a low-temperature (? 120 °C) 'in-situ' baking of the cavity if the chemical treatment was EP rather than BCP. As part of the effort to understand this phenomenon, we investigated the effect of introducing a polarization potential during buffered chemical polishing, creating a process which is between the standard BCP and EP. While preliminary results on the application of this process to Nb cavities have been previously reported, in this contribution we focus on the characterization of this novel electrochemical process by measuring polarization curves, etching rates, surface finish, electrochemical impedance and the effects of temperature and electrolyte composition. In particular, it is shown that the anodic potential of Nb during BCP reduces the etching rate and improves the surface finish.

  12. Melting And Purification Of Niobium

    SciTech Connect

    Salles Moura, Hernane R.; Moura, Lourenco de

    2007-08-09

    The aspects involved in the purification of niobium in Electron Beam Furnaces will be outlined and correlated with practical experience accumulated over 17 years of continuously producing high purity niobium metal and niobium-zirconium ingots at CBMM, meeting the needs for a wide range of uses. This paper also reports some comments regarding raw material requirements, the experience on cold hearth operation melting niobium and the production of large grains niobium ingots by CBMM with some comments of their main characteristics.

  13. Melting And Purification Of Niobium

    NASA Astrophysics Data System (ADS)

    Moura, Hernane R. Salles; de Moura, Lourenço

    2007-08-01

    The aspects involved in the purification of niobium in Electron Beam Furnaces will be outlined and correlated with practical experience accumulated over 17 years of continuously producing high purity niobium metal and niobium-zirconium ingots at CBMM, meeting the needs for a wide range of uses. This paper also reports some comments regarding raw material requirements, the experience on cold hearth operation melting niobium and the production of large grains niobium ingots by CBMM with some comments of their main characteristics.

  14. Nitrogen doping study in ingot niobium cavities

    SciTech Connect

    Dhakal, Pashupati; Ciovati, Gianluigi; Kneisel, Peter; Myneni, Ganapati Rao; Makita, Junki

    2015-09-01

    Thermal diffusion of nitrogen in niobium superconducting radio frequency cavities at temperature ~800 °C has resulted in the increase in quality factor with a low-field Q-rise extending to Bp > 90 mT. However, the maximum accelerating gradient of these doped cavities often deteriorates below the values achieved by standard treatments prior to doping. Here, we present the results of the measurements on ingot niobium cavities doped with nitrogen at 800 °C. The rf measurements were carried out after the successive electropolishing to remove small amount of material from the inner surface layer. The result showed higher breakdown field with lower quality factor as material removal increases.

  15. Development of high purity niobium used in SRF accelerating cavity

    NASA Astrophysics Data System (ADS)

    Chen, Lin; Xie, Wei-Ping; Li, Ming-Yang; He, Ji-Lin; Fan, Hui-Ru; Zhang, Bao-Cheng; He, Fei-Si; Zhao, Kui; Chen, Jia-Er; Liu, Ke-Xin

    2008-12-01

    Niobium is widely used in SRF (Superconducting Radio Frequency) cavities due to its excellent superconductivity and workability. With the continuous development of technology, higher demands of material are raised. One of the key issues is that RRR (Residual Resistance Ratio) of the Nb material should be more than 300, which requires that the Nb ingot have even higher RRR. This article introduces the development and the experimental results of high purity niobium in OTIC in Ningxia (Ningxia Orient Tantalum Industry Co. Ltd.), and the test results of the single cell TESLA (Tera Electron volt energy Superconducting Linear Accelerator) shaped cavity manufactured by Peking University using Nb material from OTIC. Supported by National Basic Research Program of China (2002CB713600)

  16. Recent developments in high purity niobium metal production at CBMM

    NASA Astrophysics Data System (ADS)

    Abdo, Gustavo Giovanni Ribeiro; Sousa, Clovis Antonio de Faria; Guimarães, Rogério Contato; Ribas, Rogério Marques; Vieira, Alaércio Salvador Martins; Menezes, Andréia Duarte; Fridman, Daniel Pallos; Cruz, Edmundo Burgos

    2015-12-01

    CBMM is a global supplier of high quality niobium products including pure niobium, the focus of this paper. CBMM's position has been consolidated over three decades of producing high purity niobium metal ingots. The company supplies, among other products, commercial and reactor grade niobium ingots. One of the main uses of CBMM's ingots is for the manufacture of particle accelerators (superconducting radio frequency - SRF - cavities), where the purity and homogeneity of niobium metal is essentially important for good performance. CBMM constantly strives to improve process controls and product quality, and is currently implementing innovations in production, research and development to further improve ingot quality. The main aim is to reduce the content of interstitial elements, such as nitrogen (N), oxygen (O), carbon (C), and hydrogen (H), starting with the raw materials through the final step of ingot production. CBMM held the first trial to produce the world's largest-diameter niobium ingot (as cast 535 mm). The results of this initial trial presented very low levels of interstitial impurities (N, O, C, H), allowing the achievement of residual resistivity ratio (RRR) values very close to 300 in a six-melt process in an electron beam furnace. These values were reached with 850 ppm of tantalum. SRF cavities will be produced with this material in order to study the effect of low impurities and high RRR on the Q factor and accelerating gradient.

  17. Recent developments in high purity niobium metal production at CBMM

    SciTech Connect

    Abdo, Gustavo Giovanni Ribeiro Sousa, Clovis Antonio de Faria Guimarães, Rogério Contato Ribas, Rogério Marques Vieira, Alaércio Salvador Martins Menezes, Andréia Duarte Fridman, Daniel Pallos Cruz, Edmundo Burgos

    2015-12-04

    CBMM is a global supplier of high quality niobium products including pure niobium, the focus of this paper. CBMM’s position has been consolidated over three decades of producing high purity niobium metal ingots. The company supplies, among other products, commercial and reactor grade niobium ingots. One of the main uses of CBMM’s ingots is for the manufacture of particle accelerators (superconducting radio frequency – SRF – cavities), where the purity and homogeneity of niobium metal is essentially important for good performance. CBMM constantly strives to improve process controls and product quality, and is currently implementing innovations in production, research and development to further improve ingot quality. The main aim is to reduce the content of interstitial elements, such as nitrogen (N), oxygen (O), carbon (C), and hydrogen (H), starting with the raw materials through the final step of ingot production. CBMM held the first trial to produce the world’s largest-diameter niobium ingot (as cast 535 mm). The results of this initial trial presented very low levels of interstitial impurities (N, O, C, H), allowing the achievement of residual resistivity ratio (RRR) values very close to 300 in a six-melt process in an electron beam furnace. These values were reached with 850 ppm of tantalum. SRF cavities will be produced with this material in order to study the effect of low impurities and high RRR on the Q factor and accelerating gradient.

  18. Status of Nb-Pb superconducting RF-gun cavities

    SciTech Connect

    J. Sekutowicz; J. Iversen; D. Klinke; D. Kostin; W. Möller; A. Muhs; P. Kneisel; J. Smedley; T. Rao; P. Strzyżewski; Z. Li; K. Ko; L. Xiao; R. Lefferts; A. Lipski; M. Ferrario

    2007-06-01

    We report on the progress in the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead. Measured values of quantum efficiency for lead at 2K and the RF-performance of three half-cell niobium cavities with the lead spot exposed to high electric fields are reported in this contribution.

  19. SRF niobium characterization using SIMS and FIB-TEM

    SciTech Connect

    Stevie, F. A.

    2015-12-04

    Our understanding of superconducting radio frequency (SRF) accelerator cavities has been improved by elemental analysis at high depth resolution and by high magnification microscopy. This paper summarizes the technique development and the results obtained on poly-crystalline, large grain, and single crystal SRF niobium. Focused ion beam made possible sample preparation using transmission electron microscopy and the images obtained showed a very uniform oxide layer for all samples analyzed. Secondary ion mass spectrometry indicated the presence of a high concentration of hydrogen and the hydrogen content exhibited a relationship with improvement in performance. Depth profiles of carbon, nitrogen, and oxygen did not show major differences with heat treatment. Niobium oxide less than 10 nm thick was shown to be an effective hydrogen barrier. Niobium with titanium contamination showed unexpected performance improvement.

  20. SRF niobium characterization using SIMS and FIB-TEM

    NASA Astrophysics Data System (ADS)

    Stevie, F. A.

    2015-12-01

    Our understanding of superconducting radio frequency (SRF) accelerator cavities has been improved by elemental analysis at high depth resolution and by high magnification microscopy. This paper summarizes the technique development and the results obtained on poly-crystalline, large grain, and single crystal SRF niobium. Focused ion beam made possible sample preparation using transmission electron microscopy and the images obtained showed a very uniform oxide layer for all samples analyzed. Secondary ion mass spectrometry indicated the presence of a high concentration of hydrogen and the hydrogen content exhibited a relationship with improvement in performance. Depth profiles of carbon, nitrogen, and oxygen did not show major differences with heat treatment. Niobium oxide less than 10 nm thick was shown to be an effective hydrogen barrier. Niobium with titanium contamination showed unexpected performance improvement.

  1. Temperature dependence measurements of the supercurrent-phase relationship in niobium nanobridges

    NASA Astrophysics Data System (ADS)

    Troeman, A. G. P.; van der Ploeg, S. H. W.; Il'Ichev, E.; Meyer, H.-G.; Golubov, A. A.; Kupriyanov, M. Yu.; Hilgenkamp, H.

    2008-01-01

    The current-phase relationship has been measured as a function of temperature for niobium nanobridges with different widths. A deformation from Josephson-like sinusoidal characteristics at high temperatures to sawtooth shaped curves at intermediate and multivalued relationships at low temperatures was observed. Based on this, possible hysteresis in the current-voltage characteristics of niobium nanobridge superconducting quantum interference devices can be attributed to phase slippage.

  2. METHOD OF PRODUCING NIOBIUM METAL

    DOEpatents

    Wilhelm, H.A.; Stevens, E.R.

    1960-05-24

    A process is given for preparing ductile niobium metal by the reduction of niobium pentoxide with carbon. The invention resides in the addition, to the reaction mass, of from 0.05 to 0.4 atom of titanium (in the form of metallic titanium, titanium carbide, and/or titanium oxide) per one mole of niobium pentoxide. The mixture is heated under subatmospheric pressure to above 1300 deg C but below the melting point of niobium, and the carbon- and oxygen-free niobium sponge obtained is cooled under reduced pressure.

  3. Magnetic Property in Large Array Niobium Antidot Thin Films

    NASA Astrophysics Data System (ADS)

    Tinghui, Chen; Hsiang-Hsi, Kung; Wei-Li, Lee; Institute of Physics, Academia Sinica, Taipei, Taiwan Team

    2014-03-01

    In a superconducting ring, the total flux inside the ring is required to be an integer number of the flux quanta. Therefore, a supercurrent current can appear within the ring in order to satisfy this quantization rule, which gives rise to certain magnetic response. By using a special monolayer polymer/nanosphere hybrid we developed previously, we fabricated a series of superconducting niobium antidot thin films with different antidot diameters. The antidots form well-ordered triangular lattice with a lattice spacing about 200 nm and extend over an area larger than 1 cm2, which enables magnetic detections simply by a SQUID magnetometer. We observed magnetization oscillation with external magnetic field due to the supercurrent screening effect, where different features for large and small antidot thin films were found. Detailed size and temperature dependencies of the magnetization in niobium antidot nanostructures will be presented.

  4. Temperature dependence of penetration depth in thin film niobium

    NASA Technical Reports Server (NTRS)

    More, N.; Muhlfelder, B.; Lockhart, J.

    1989-01-01

    A novel technique is presented which should allow precise determination of the temperature dependence of the inductance, and hence of the penetration depth, of superconducting niobium thin-film structures. Four niobium thin-film stripline inductors are arranged in a bridge configuration, and inductance differences are measured using a potentiometric technique with a SQUID (superconducting quantum interference device) as the null detector. Numerical simulations of the stripline inductances are presented which allow the performance of the measurement technique to be evaluated. The prediction of the two-fluid model for the penetration-depth temperature dependence is given for reduced temperatures of 0.3 to 0.9. The experimental apparatus and its resolution and accuracy are discussed.

  5. Low-gravity processing of superconducting compounds

    NASA Technical Reports Server (NTRS)

    Otto, G. H.

    1976-01-01

    Low gravity conditions can be sustained on earth for several seconds in an evacuated drop tube. Because radiation cooling is most effective at high temperatures, the refractive metals and alloys are prime candidates for free fall solidification. The results of initial experiments on droplet formation, droplet release, critical size and evaporation losses are given. The time required for free fall solidification of different size droplets is calculated. The materials studied were copper, niobium and vanadium, and a niobium-tin alloys. Improvements in purity, composition, homogeneity and stoichiometry are expected during free fall solidification of niobium based alloys which should become evident in an increase in the superconducting transition temperature.

  6. Prototype 350 MHz niobium spoke-loaded cavities.

    SciTech Connect

    Delayen, J. R.; Kedzie, M.; Mammosser, J.; Piller, C.; Shepard, K. W.

    1999-05-10

    This paper reports the development of 350 MHz superconducting cavities of a spoke-loaded geometry, intended for the velocity range 0.2 < v/c < 0.6. Two prototype single-cell cavities have been designed, one optimized for velocity v/c = 0.4, and the other for v/c = 0.29. Construction of the prototype niobium cavities is nearly complete. Details of the design and construction are discussed, along with the results of cold tests.

  7. Intrabeam stripping in H- Linacs

    SciTech Connect

    Lebedev, V.; Solyak, N.; Ostigy, J.-F.; Alexandrov, A.; Shishlo, A.; /Oak Ridge

    2010-09-01

    A beam loss in the superconducting part of the SNS linac has been observed during its commissioning and operation. Although the loss does not prevent the SNS high power operation, it results in an almost uniform irradiation of linac components and increased radiation levels in the tunnel. Multi-particle tracking could neither account for the magnitude of the observed loss nor its dependence on machine parameters. It was recently found that the loss is consistent with the intrabeam particle collisions resulting in stripping of H{sup -} ions. The paper describes experimental observations and corresponding analytical estimates of the intrabeam stripping.

  8. Stable superconducting magnet. [high current levels below critical temperature

    NASA Technical Reports Server (NTRS)

    Boom, R. W. (Inventor)

    1967-01-01

    Operation of a superconducting magnet is considered. A method is described for; (1) obtaining a relatively high current in a superconducting magnet positioned in a bath of a gas refrigerant; (2) operating a superconducting magnet at a relatively high current level without training; and (3) operating a superconducting magnet containing a plurality of turns of a niobium zirconium wire at a relatively high current level without training.

  9. Superconducting Radio Frequency Technology: An Overview

    SciTech Connect

    Peter Kneisel

    2003-06-01

    Superconducting RF cavities are becoming more often the choice for larger scale particle accelerator projects such as linear colliders, energy recovery linacs, free electron lasers or storage rings. Among the many advantages compared to normal conducting copper structures, the superconducting devices dissipate less rf power, permit higher accelerating gradients in CW operation and provide better quality particle beams. In most cases these accelerating cavities are fabricated from high purity bulk niobium, which has superior superconducting properties such as critical temperature and critical magnetic field when compared to other superconducting materials. Research during the last decade has shown, that the metallurgical properties--purity, grain structure, mechanical properties and oxidation behavior--have significant influence on the performance of these accelerating devices. This contribution attempts to give a short overview of the superconducting RF technology with emphasis on the importance of the material properties of the high purity niobium.

  10. Method of surface preparation of niobium

    SciTech Connect

    Srinivasan-Rao, Triveni; Schill, John F.

    2003-01-01

    The present invention is for a method of preparing a surface of niobium. The preparation method includes polishing, cleaning, baking and irradiating the niobium surface whereby the resulting niobium surface has a high quantum efficiency.

  11. Vapor deposition of hardened niobium

    DOEpatents

    Blocher, Jr., John M.; Veigel, Neil D.; Landrigan, Richard B.

    1983-04-19

    A method of coating ceramic nuclear fuel particles containing a major amount of an actinide ceramic in which the particles are placed in a fluidized bed maintained at ca. 800.degree. to ca. 900.degree. C., and niobium pentachloride vapor and carbon tetrachloride vapor are led into the bed, whereby niobium metal is deposited on the particles and carbon is deposited interstitially within the niobium. Coating apparatus used in the method is also disclosed.

  12. Improved superconducting magnet wire

    DOEpatents

    Schuller, I.K.; Ketterson, J.B.

    1983-08-16

    This invention is directed to a superconducting tape or wire composed of alternating layers of copper and a niobium-containing superconductor such as niobium of NbTi, Nb/sub 3/Sn or Nb/sub 3/Ge. In general, each layer of the niobium-containing superconductor has a thickness in the range of about 0.05 to 1.5 times its coherence length (which for Nb/sub 3/Si is 41 A) with each copper layer having a thickness in the range of about 170 to 600 A. With the use of very thin layers of the niobium composition having a thickness within the desired range, the critical field (H/sub c/) may be increased by factors of 2 to 4. Also, the thin layers of the superconductor permit the resulting tape or wire to exhibit suitable ductility for winding on a magnet core. These compositions are also characterized by relatively high values of critical temperature and therefore will exhibit a combination of useful properties as superconductors.

  13. Thermal and quantum phase slips in niobium-nitride nanowires based on suspended carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Masuda, Kohei; Moriyama, Satoshi; Morita, Yoshifumi; Komatsu, Katsuyoshi; Takagi, Tasuku; Hashimoto, Takayuki; Miki, Norihisa; Tanabe, Takasumi; Maki, Hideyuki

    2016-05-01

    Superconducting nanowires have attracted considerable attention due to their unique quantum-mechanical properties, as well as their potential as next-generation quantum nanodevices, such as single-photon detectors, phase-slip (PS) qubits, and other hybrid structures. In this study, we present the results of one-dimensional (1D) superconductivity in nanowires fabricated by coating suspended carbon nanotubes with a superconducting thin niobium nitride (NbN) film. In the resistance-temperature characteristic curves, hallmarks of 1D superconductivity with PS events are observed with unconventional negative magnetoresistance. We also confirm that a crossover occurs between thermal and quantum PSs as the temperature is lowered.

  14. Niobium Thin Film Properties Affected by Deposition Energy during Vacuum Deposition

    SciTech Connect

    Genfa Wu; H. Phillips; Ronald Sundelin; Anne-Marie Valente

    2003-05-01

    In order to understand and improve the super-conducting performance of niobium thin films at cryogenic temperatures, an energetic vacuum deposition system has been developed to study deposition energy effects on the properties of niobium thin films on various substrates. Ultra high vacuum avoids the gaseous inclusions in thin films commonly seen in sputtering deposition. A retarding field energy analyzer is used to measure the kinetic energy of niobium ions at the substrate location. A biased substrate holder controls the deposition energy. Transition temperature and residual resistivity ratio (RRR) of the niobium thin films at several deposition energies are obtained together with crystal orientation measurements and atomic force microscope (AFM) inspection, and the results show that there exists a preferred deposition energy around 115eV (the average deposition energy 64 eV plus the 51 V bias voltage).

  15. Stripping Voltammetry

    NASA Astrophysics Data System (ADS)

    Lovrić, Milivoj

    Electrochemical stripping means the oxidative or reductive removal of atoms, ions, or compounds from an electrode surface (or from the electrode body, as in the case of liquid mercury electrodes with dissolved metals) [1-5]. In general, these atoms, ions, or compounds have been preliminarily immobilized on the surface of an inert electrode (or within it) as the result of a preconcentration step, while the products of the electrochemical stripping will dissolve in the electrolytic solution. Often the product of the electrochemical stripping is identical to the analyte before the preconcentration. However, there are exemptions to these rules. Electroanalytical stripping methods comprise two steps: first, the accumulation of a dissolved analyte onto, or in, the working electrode, and, second, the subsequent stripping of the accumulated substance by a voltammetric [3, 5], potentiometric [6, 7], or coulometric [8] technique. In stripping voltammetry, the condition is that there are two independent linear relationships: the first one between the activity of accumulated substance and the concentration of analyte in the sample, and the second between the maximum stripping current and the accumulated substance activity. Hence, a cumulative linear relationship between the maximum response and the analyte concentration exists. However, the electrode capacity for the analyte accumulation is limited and the condition of linearity is satisfied only well below the electrode saturation. For this reason, stripping voltammetry is used mainly in trace analysis. The limit of detection depends on the factor of proportionality between the activity of the accumulated substance and the bulk concentration of the analyte. This factor is a constant in the case of a chemical accumulation, but for electrochemical accumulation it depends on the electrode potential. The factor of proportionality between the maximum stripping current and the analyte concentration is rarely known exactly. In fact

  16. Enhanced characterization of niobium surface topography

    NASA Astrophysics Data System (ADS)

    Xu, Chen; Tian, Hui; Reece, Charles E.; Kelley, Michael J.

    2011-12-01

    Surface topography characterization is a continuing issue for the superconducting radio frequency (SRF) particle accelerator community. Efforts are under way to both improve surface topography and its characterization and analysis using various techniques. In measurement of topography, power spectral density (PSD) is a promising method to quantify typical surface parameters and develop scale-specific interpretations. PSD can also be used to indicate how the process modifies topography at different scales. However, generating an accurate and meaningful topographic PSD of an SRF surface requires careful analysis and optimization. In this report, niobium surfaces with different process histories are sampled with atomic force microscopy and stylus profilometry and analyzed to trace topography evolution at different scales. An optimized PSD analysis protocol to serve SRF needs is presented.

  17. Large grain cavities from pure niobium ingot

    DOEpatents

    Myneni, Ganapati Rao; Kneisel, Peter; Cameiro, Tadeu

    2012-03-06

    Niobium cavities are fabricated by the drawing and ironing of as cast niobium ingot slices rather than from cold rolled niobium sheet. This method results in the production of niobium cavities having a minimum of grain boundaries at a significantly reduced cost as compared to the production of such structures from cold rolled sheet.

  18. High energy H- ion transport and stripping

    SciTech Connect

    Chou, W.; /Fermilab

    2005-05-01

    During the Proton Driver design study based on an 8 GeV superconducting RF H{sup -} linac, a major concern is the feasibility of transport and injection of high energy H{sup -} ions because the energy of H{sup -} beam would be an order of magnitude higher than the existing ones. This paper will focus on two key technical issues: (1) stripping losses during transport (including stripping by blackbody radiation, magnetic field and residual gases); (2) stripping efficiency of carbon foil during injection.

  19. NIOBIUM-TANTALUM SEPARATION

    DOEpatents

    Wilhelm, H.A.; Foos, R.A.

    1959-01-27

    The usual method for the separation of tantalum and niobium consists of a selective solvent extraction from an aqueous hydrofluoric acid solution of the metals. A difficulty encountered in this process is the fact that the corrosion problems associated with hydrofluoric acid are serious. It has been found that the corrosion caused by the hydrofluoric acid may be substantially reduced by adding to the acidic solution an amine, such as phenyl diethanolamine or aniline, and adjusting pH value to between 4 and 6.

  20. Fabrication techniques for superconducting readout loops

    NASA Technical Reports Server (NTRS)

    Payne, J. E.

    1982-01-01

    Procedures for the fabrication of superconducting readout loops out of niobium on glass substrates were developed. A computer program for an existing fabrication system was developed. Both positive and negative resist procedures for the production of the readout loops were investigated. Methods used to produce satisfactory loops are described and the various parameters affecting the performance of the loops are analyzed.

  1. Tensile tests of niobium material for SRF cavities

    SciTech Connect

    Wu, G.; Dhanaraj, N.; Cooley, L.; Hicks, D.; Hahn, E.; Burk, D.; Muranyi, W.; Foley, N.; Edwards, H.; Harms, E.; Champion, M.; /Fermilab /Michigan State U.

    2009-06-01

    Mechanical tests of cavity-grade niobium samples were conducted to provide engineering information for the certification of 3rd-harmonic superconducting radio-frequency cavities and cryomodules. Large changes of mechanical properties occur throughout the cavity fabrication process due to the cold work introduced by forming, the heating introduced by electron beam welding, and the recovery of cold work during the anneal used to degas hydrogen after chemical processing. Data is provided here to show the different properties at various stages of fabrication, including both weld regions and samples from the bulk niobium far away from the weld. Measurements of RRR were used to assure that any contamination during annealing was negligible.

  2. Tensile Tests of Niobium Material for Srf Cavities

    NASA Astrophysics Data System (ADS)

    Wu, G.; Dhanaraj, N.; Cooley, L.; Hicks, D.; Hahn, E.; Burk, D.; Muranyi, W.; Foley, M.; Edwards, H.; Harms, E.; Champion, M.; Baars, D.; Compton, C.

    2010-04-01

    Mechanical tests of cavity-grade niobium samples were conducted to provide engineering information for the certification of 3rd-harmonic superconducting radio-frequency cavities and cryomodules. Large changes of mechanical properties occur throughout the cavity fabrication process due to the cold work introduced by forming, the heating introduced by electron beam welding, and the recovery of cold work during the anneal used to degas hydrogen after chemical processing. Data is provided here to show the different properties at various stages of fabrication, including both weld regions and samples from the bulk niobium far away from the weld. Measurements of RRR were used to assure that any contamination during annealing was negligible.

  3. Robotic Stripping

    NASA Technical Reports Server (NTRS)

    2000-01-01

    UltraStrip Systems, Inc.'s M-200 removes paint from the hulls of ships faster than traditional grit-blasting methods. And, it does so without producing toxic airborne particles common to traditional methods. The M-2000 magnetically attaches itself to the hull of the ship. Its water jets generate 40,000 pounds of pressure per square inch, blasting away paint down to the ships steel substrate. The only by product is water and dried paint chips and these are captured by a vacuum system so no toxic residue can escape. It was built out of a partnership between the Jet Propulsion Laboratory and the National Robotics Engineering Consortium.

  4. A simple method for characterizing the RF properties of high-temperature superconductive materials

    NASA Technical Reports Server (NTRS)

    Chang, K.; Pandey, R. K.; Skrehot, M. K.; Li, M.

    1989-01-01

    A simple method using a resonant strip in a rectangular waveguide has been devised for superconductive material characterization. The method has the advantages of simplicity; and it requires only a small piece of the superconductive material. The resonant frequency of the superconductive strip can be predicted theoretically.

  5. Status of Nb-Pb Superconducting RF-Gun Cavities

    SciTech Connect

    Sekutowicz, J.; Iversen, J.; Klinke, D.; Kostin, D.; Moller, W.; Muhs, A.; Kneisel, P.; Smedley, J.; Rao, T.; Strzyzewski, P.; Li, Z.; Ko, K.; Xiao, L.; Lefferts, R.; Lipski, A.; Ferrario, M.; /Frascati

    2007-11-09

    We report on the progress and status of an electron RFgun made of two superconductors: niobium and lead [1]. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead. The design of RF-gun and performance of 3 test cavities without and with the emitting lead spot are reported in this contribution. Measured quantum efficiency for lead at 2K is presented briefly. More details are reported in [9].

  6. Method of making an improved superconducting quantum interference device

    DOEpatents

    Wu, Cheng-Teh; Falco, Charles M.; Kampwirth, Robert T.

    1977-01-01

    An improved superconducting quantum interference device is made by sputtering a thin film of an alloy of three parts niobium to one part tin in a pattern comprising a closed loop with a narrow region, depositing a thin film of a radiation shield such as copper over the niobium-tin, scribing a narrow line in the copper over the narrow region, exposing the structure at the scribed line to radiation and removing the deposited copper.

  7. Diamond magnetometry of Meissner currents in a superconducting film

    NASA Astrophysics Data System (ADS)

    Alfasi, Nir; Masis, Sergei; Shtempluck, Oleg; Kochetok, Valleri; Buks, Eyal

    2016-07-01

    We study magnetic field penetration into a thin film made of a superconducting niobium. Imaging of magnetic field is performed by optically detecting magnetic resonances of negatively charged nitrogen-vacancy defects inside a single crystal diamond, which is attached to the niobium film under study. The experimental results are compared with theoretical predictions based on the critical state model, and good agreement is obtained.

  8. Niobium and tantalum: indispensable twins

    USGS Publications Warehouse

    Schulz, Klaus; Papp, John

    2014-01-01

    Niobium and tantalum are transition metals almost always paired together in nature. These “twins” are difficult to separate because of their shared physical and chemical properties. In 1801, English chemist Charles Hatchett uncovered an unknown element in a mineral sample of columbite; John Winthrop found the sample in a Massachusetts mine and sent it to the British Museum in London in 1734. The name columbium, which Hatchet named the new element, came from the poetic name for North America—Columbia—and was used interchangeably for niobium until 1949, when the name niobium became official. Swedish scientist Anders Ekberg discovered tantalum in 1802, but it was confused with niobium, because of their twinned properties, until 1864, when it was recognized as a separate element. Niobium is a lustrous, gray, ductile metal with a high melting point, relatively low density, and superconductor properties. Tantalum is a dark blue-gray, dense, ductile, very hard, and easily fabricated metal. It is highly conductive to heat and electricity and renowned for its resistance to acidic corrosion. These special properties determine their primary uses and make niobium and tantalum indispensable.

  9. METHOD FOR COATING GRAPHITE WITH NIOBIUM CARBIDE

    DOEpatents

    Kane, J.S.; Carpenter, J.H.; Krikorian, O.H.

    1962-01-16

    A method is given for coating graphite with a hard, tenacious layer of niobium carbide up to 30 mils or more thick. The method makes use of the discovery that niobium metal, if degassed and heated rapidly below the carburization temperature in contact with graphite, spreads, wets, and penetrates the graphite without carburization. The method includes the obvious steps of physically contacting niobium powders or other physical forms of niobium with graphite, degassing the assembly below the niobium melting point, e.g., 1400 deg C, heating to about 2200 to 2400 deg C within about 15 minutes while outgassing at a high volume throughput, and thereafter carburizing the niobium. (AEC)

  10. Photoemission tests of a Pb/Nb superconducting photoinjector

    SciTech Connect

    J. Smedley; J. Iversen; D. Klinke; D. Kostin; W.-D. Moller; A. Muhs; J. S. Sekutowicz; P. Kneisel; R. S. Lefferts, A. R. Lipski; T. Rao

    2007-06-01

    We report recent progress in the development of a hybrid lead/niobium superconducting (SC) injector. The goal of this effort is to produce an all-SC injector with the SCRF properties of a niobium cavity along with the superior quantum efficiency (QE) of a lead photocathode. Two prototype hybrid injectors have been constructed, one utilizing a cavity with a removable cathode plug, and a second consisting of an all-niobium cavity arc-deposited with lead in the cathode region. We present the results of QE measurements on these cavities, along with tests of the effect of the laser on the cavity RF performance.

  11. Direct Flotation of Niobium Oxide Minerals from Carbonatite Niobium Ores

    NASA Astrophysics Data System (ADS)

    Ni, Xiao

    Currently the recovery of niobium oxide minerals from carbonatite niobium ores relies on the use of non-selective cationic collectors. This leads to complicated process flowsheets involving multiple desliming and multiple reverse flotation stages, and low niobium recovery. In this research, anionic collectors that are capable of strong chemisorption on the niobium minerals were studied with the objective of directly floating the niobium oxide minerals from the carbonatite ores. In the flotation of both high purity minerals and Niobec ores, it was shown that the combination of hydroxamic acid and sodium metaphosphate was an effective reagent scheme for the direct flotation of niobium oxide from its ores. Batch flotation on the Niobec Mill Feed showed that over 95% of niobium oxide was recovered into a rougher concentrate that was less than 47% of the original feed mass. Preliminary cleaning tests showed that the reagent scheme could also be used to upgrade the rougher concentrate, although the depression of iron oxide minerals required further study. X-ray photoelectron spectroscopic (XPS) measurement results confirm that OHA (octyl hydroxamic acid) could chemisorb on pyrochlore surface while only physically adsorb on calcite, judging by the chemical shifts of electron binding energies in the elements in both OHA and the mineral surfaces. When hydroxamic acid was adsorbed on calcite surface, the binding energies of the N 1s electrons, at 400.3 eV, did not shift. However, after adsorption on pyrochlore, the N 1s binding energy peak split into two peaks, one at a binding energy of around 399 eV, representing chemically adsorbed OHA, the other at between 400 and 401 eV. The experimental data suggested a strong chemisorption of the OHA on pyrochlore surface in the form of a vertical head-on orientation of the OHA molecules so that the pyrochlore was strongly hydrophobized even at low OHA concentrations, followed by possibly randomly oriented physisorbed OHA molecules

  12. Niobium - Proceedings of the international symposium

    SciTech Connect

    Stuart, H.

    1984-01-01

    This book presents the papers given at a symposium on niobium. Topics considered at the symposium included niobium mining, ore processing, uses, fabrication, microstructure, mechanical properties, physical properties, corrosion, physical radiation effects, and marketing.

  13. Microtube Strip Heat Exchanger

    SciTech Connect

    Doty, F.D.

    1990-12-27

    Doty Scientific (DSI) believes their Microtube-Strip Heat Exchanger will contribute significantly to (a) the closed Brayton cycles being pursued at MIT, NASA, and elsewhere; (b) reverse Brayton cycle cryocoolers, currently being investigated by NASA for space missions, being applied to MRI superconducting magnets; and (c) high-efficiency cryogenic gas separation schemes for CO{sub 2} removal from exhaust stacks. The goal of this current study is to show the potential for substantial progress in high-effectiveness, low-cost, gas-to-gas heat exchangers for diverse applications at temperatures from below 100 K to above 1000 K. To date, the highest effectiveness measured is about 98%, and relative pressure drops below 0.1% with a specific conductance of about 45 W/kgK are reported. During the pre-award period DSI built and tested a 3-module heat exchanger bank using 103-tube microtube strip (MTS) modules. To add to their analytical capabilities, DSI has acquired computational fluid dynamics (CFD) software. This report describes the pre-award work and the status of the ten tasks of the current project, which are: analyze flow distribution and thermal stresses within individual modules; design a heat exchanger bank of ten modules with 400 microtube per module; obtain production quality tubestrip die and AISI 304 tubestrips; obtain production quality microtubing; construct revised MTS heat exchanger; construct dies and fixtures for prototype heat exchanger; construct 100 MTS modules; assemble 8-10 prototype MTS heat exchangers; test prototype MTS heat exchanger; and verify test through independent means. 7 refs., 9 figs. 1 tab. (CK)

  14. Field dependent surface resistance of niobium on copper cavities

    NASA Astrophysics Data System (ADS)

    Junginger, T.

    2015-07-01

    The surface resistance RS of superconducting cavities prepared by sputter coating a niobium film on a copper substrate increases significantly stronger with the applied rf field compared to cavities of bulk material. A possible cause is that the thermal boundary resistance between the copper substrate and the niobium film induces heating of the inner cavity wall, resulting in a higher RS. Introducing helium gas in the cavity, and measuring its pressure as a function of applied field allowed to conclude that the inner surface of the cavity is heated up by less than 120 mK when RS increases with Eacc by 100 n Ω . This is more than one order of magnitude less than what one would expect from global heating. Additionally, the effects of cooldown speed and low temperature baking have been investigated in the framework of these experiments. It is shown that for the current state of the art niobium on copper cavities there is only a detrimental effect of low temperature baking. A fast cooldown results in a lowered RS.

  15. Effect of low temperature baking on niobium cavities

    SciTech Connect

    Peter Kneisel; Ganapati Myneni; William Lanford; Gianluigi Ciovati

    2003-09-01

    A low temperature (100 C-150 C) ''in situ'' baking under ultra-high vacuum has been successfully applied as final preparation of niobium RF cavities by several laboratories over the last few years. The benefits reported consist mainly of an improvement of the cavity quality factor and a recovery from the so-called ''Q-drop'' without field emission at high field. A series of experiments with a CEBAF single cell cavity have been carried out at Jefferson Lab to carefully investigate the effect of baking at progressively higher temperatures for a fixed time on all the relevant material parameters. Measurements of the cavity quality factor in the temperature range 1.37K-280K and resonant frequency shift between 6K-9.3K provide information about the surface resistance, energy gap, penetration depth and mean free path. The experimental data have been analyzed with the complete BCS theory of superconductivity using a modified version of the computer code originally written by J. Halbritter [1] . Small niobium samples inserted in the cavity during its surface preparation were analyzed with respect to their hydrogen content with a Nuclear Reaction Analysis (NRA). The single cell cavity has been tested at three different temperatures before and after baking to gain some insight on thermal conductivity and Kapitza resistance and the data are compared with different models. This paper describes the results from these experiments and comments on the existing models to explain the effect of baking on the performance of niobium RF cavities.

  16. Surface Participation Effects in Titanium Nitride and Niobium Resonators

    NASA Astrophysics Data System (ADS)

    Dove, Allison; Kreikebaum, John Mark; Livingston, William; Delva, Remy; Qiu, Yanjie; Lolowang, Reinhard; Ramasesh, Vinay; O'Brien, Kevin; Siddiqi, Irfan

    Improving the coherence time of superconducting qubits requires a precise understanding of the location and density of surface defects. Superconducting microwave resonators are commonly used for quantum state readout and are a versatile testbed to systematically characterize materials properties as a function of device geometry and fabrication method. We report on sputter deposited titanium nitride and niobium on silicon coplanar waveguide resonators patterned using reactive ion etches to define the device geometry. We discuss the impact of different growth conditions (temperature and electrical bias) and processing techniques on the internal quality factor (Q) of these devices. In particular, to investigate the effect of surface participation, we use a Bosch process to etch many-micron-deep trenches in the silicon substrate and quantify the impact of etch depth and profile on the internal Q. This research was supported by the ARO.

  17. State of the Art Power-in Tube Niobium-Tin Superconductors

    SciTech Connect

    Godeke, A.; Ouden, A. Den; Nijhuis, A.; ten Kate, H.H.J.

    2008-06-01

    Powder-in-Tube (PIT) processed Niobium-Tin wires are commercially manufactured for nearly three decades and have demonstrated a combination of very high current density (presently up to 2500 A mm{sup -2} non-Cu at 12 T and 4.2 K) with fine (35 {micro}m), well separated filaments. We review the developments that have led to the present state of the art PIT Niobium-Tin wires, discuss the wire manufacturing and A15 formation processes, and describe typical superconducting performance in relation to magnetic field and strain. We further highlight successful applications of PIT wires and conclude with an outlook on possibilities for further improvements in the performance of PIT Niobium-Tin wires.

  18. CRADA 2009S001: Investigation of the Supercondcuting RF Properties of Large Grain Ingot Niobium

    SciTech Connect

    Grimm, Terry; Hollister, Jerry L.; Kolka, Ahren; Myneni, Ganapati Rao

    2012-12-18

    This CRADA intended to explore the properties of large grain ingot niobium by fabricating four single cell TESLA shaped accelerating cavities. Once the cavities were fabricated, SRF performance would be measured. Niowave received four discs of large grain ingot niobium from JLAB in February 2009. Niowave cut samples from each disc and tested the RRR. After the RRR was measured with disappointing results, the project lost interest. A no cost extension was signed in July 2009 to allow progress until June 2010, but ultimately no further work was accomplished by either party. No firm conclusions were drawn, as further investigations were not made. Large grain ingot niobium has shown real potential for high accelerating gradient superconducting cavities. However, this particular CRADA did not gather enough data to reach any conclusions in this regard.

  19. Mechanical Properties of High Purity Niobium - Novel Measurements

    SciTech Connect

    Ganapati Myneni

    2003-09-01

    One of the procedures to improve the performance of superconducting niobium cavities is a heat treatment for several hours in an ultrahigh vacuum at temperatures between 800C and 1400C for hydrogen degassing or post-purification, respectively. However, it was recently observed with Spallation Neutron Source Project (SNS) prototype cavities, that a heat treatment at 800 C for even 1 hour degraded the mechanical properties of RRR niobium, in particular the yield strength. This lower strength resulted in cavity deformations during handling thus affecting both their resonant frequency and field profile. In addition to lowering the yield strength, it was observed in some lots of material that the Young's modulus was also apparently reduced by a factor of 2 as a result of the hydrogen outgassing at 800 C. Surprisingly, material received at other national laboratories exhibited similar anomalous behavior even without any heat treatments in vacuum. Based on these observations a multi-institutional collaborative basic research activity on high RRR niobium (determination of Nb yield strength as a function of grain size, work hardening, chemical composition, and heat treatment temperature) has been initiated by JLAB to gain a better understanding of the material properties affecting the mechanical behavior In this contribution, a brief review of the measurements at JLAB, at the Materials Science and Engineering Department of the University of Virginia, at the Analytical Chemistry and Metallurgy Divisions of the National Institute of Standard and Technology, Gaithersburg and in the Department of Physics, SUNY, Albany are presented. The measurements include yield strength, hardness, ultrasonic velocity, crystallographic structure, microstructure, determination of interstitial contents using internal friction; particular emphasis is placed on determining the hydrogen concentration in the niobium via Cold Neutron Prompt Gamma-Ray Activation Analysis and Neutron Incoherent

  20. Development of a Niobium Bellow for Beamline Connections

    SciTech Connect

    Larry Turlington; John Brawley; Robert Manus; Stephen Manning; Samuel Morgan; Gary Slack; Peter Kneisel

    2003-09-01

    Superconducting cavities in an accelerator assembly are usually connected at the beampipes by stainless steel bellows. They operate at an intermediate temperature, compensating for alignment tolerances on the cavity beamlines and for thermal contraction during cooldown to cryogenic temperatures. This transition from one cavity to the next in a cavity string is typically of the order of 3/2 wavelength along with approximately half a wavelength taken up by the bellows. If one could incorporate a niobium bellows in the beam pipe, this distance could be reduced by half a wave length. In the case of a big accelerator such as TESLA the overall cavity length for the accelerator could be reduced by roughly 10% or 2000 m. In terms of cost savings this would amount to several million dollars. Based on this estimate we have begun to develop a niobium bellows to be used on a 2.75 inch diameter beamline. It is made from 0.3 mm thick niobium sheet, rolled into a tube and secured by a longitudinal full penetration electron beam weld; the weld is made with a high speed a narrow, focused beam reducing the heat affected zone, thus limiting the grain growth, which could affect the formability. Subsequently, two convolutions have been pressed into this tube in a 2-stage process, using an external die and a polyurethane internal expander. Niobium cuffs and flanges were electron beam welded to the formed bellows, which facilitated leak testing and allowed some measurements of compression/expansion and bending. In this contribution the fabrication process and the subsequent mechanical and vacuum tests with the bellows will be described.

  1. Plasma Treatment of Single-Cell Niobium SRF Cavities

    SciTech Connect

    J. Upadhyay, M. Nikolić, S. Popović, L. Vušković, H.L. Phillips, A-M. Valente-Feliciano

    2011-03-01

    Superconducting radio frequency cavities of bulk Niobium are integral components of particle accelerators based on superconducting technology. Wet chemical processing is the commonly used procedure for impurities and surface defects removal and surface roughness improvement , both required to improve the RF performance of the cavity. We are studying plasma etching as an alternate technique to process these cavities. The uniformity of the plasma sheath at the inner wall of the cavity is one prerequisite for its uniform etching. We are developing electro-optic diagnostic techniques to assess the plasma uniformity. Multiple electro-optical probes are placed at different locations of the single cell cavity to diagnose the electrical and optical properties of the plasma. The electrical parameters are required to understand the kinetic nature of the plasma and the optical emission spectroscopy provides the spatial distribution of radicals in the plasma. The spatial variation of the plasma parameters inside the cavity and their effect on the etching of niobium samples placed at different locations in the cavity will be presented.

  2. Using helium as background gas to avoid hydrogen brittleness for MgB2 film fabrication on niobium substrate by HPCVD

    NASA Astrophysics Data System (ADS)

    Guo, Xin; Ni, Zhimao; Chen, Lizhi; Hu, Hui; Yang, Can; Feng, Qingrong; Liu, Kexin

    2016-05-01

    Magnesium diboride has shown potential as an alternative material for the application of superconducting RF cavities. However, if MgB2 films are fabricated on niobium substrates with HPCVD method, hydrogen brittleness will cause cracks on MgB2 film when it is bent. In this work, we have investigated the possibility of depositing MgB2 film on niobium in other background gases rather than hydrogen to avoid hydrogen brittleness. Though MgB2 films fabricated in nitrogen and argon have impurities and show poor superconducting properties, the MgB2 film fabricated in helium has similar morphology and superconducting properties of that prepared in hydrogen and no cracks are observed after bending. The problem of hydrogen brittleness can be solved by using helium as the background gas when fabricating MgB2 films on niobium substrates.

  3. Materials for Accelerator Technologies Beyond the Niobium Family

    SciTech Connect

    Cooley, Lance; Larbalestier, David; Ghosh, Arup; Tollestrup, Alvin; /Fermilab

    2009-01-01

    Three niobium-based materials make up the entire present portfolio of superconducting technology for accelerators: Nb-Ti and Nb{sub 3}Sn magnet wires and pure niobium for RF cavities. Because these materials are at a high level of maturity, limits imposed by the boundaries of their superconductivity constrain the energy reach of accelerators to several TeV. We sketch here a plan for targeted development of emerging higher field and higher temperature superconductors that could enable accelerators at significantly higher energies. Niobium-based superconductors are the crucial enablers of present accelerators. The Nb-Ti LHC dipole and quadrupole wires, with transition temperature T{sub c} of 9 K and upper critical field H{sub c2} of 15 T, represent the highest form of superconductor strand art: massive, quarter-ton conductor billets are drawn from 300 mm diameter to {approx}1 mm as a single, multi-kilometer-long piece, while retaining uniformity of the several thousand Nb-Ti filaments to within 5% at the scale of a few micrometers. Strands are twisted into fully transposed cables with virtually no loss, preserving a carefully tuned nanostructure that generates the high flux-pinning forces and high current densities to enable high magnetic fields. Nb{sub 3}Sn, with twice the T{sub c} and H{sub c2}, is now approaching this level of conductor art, where over the last 5 years the LHC Accelerator Research Program (LARP) and the Next European Dipole (NED) program have demonstrated that Nb{sub 3}Sn can be made into 4 meter long quadrupoles with 12 T fields and 250 T/m gradients. Linear accelerators at TJNAF, ORNL (SNS), and under construction for the European XFEL exploit niobium superconducting radio-frequency (SRF) technology, with gradients at {approx}20 MV/m. Tremendous research and development is underway to realize high-power goals for Project X at FNAL and for a possible ILC at 35 MV/m gradients. Despite these impressive achievements, the very maturity of these

  4. Effect of interstitial impurities on the field dependent microwave surface resistance of niobium

    NASA Astrophysics Data System (ADS)

    Martinello, M.; Grassellino, A.; Checchin, M.; Romanenko, A.; Melnychuk, O.; Sergatskov, D. A.; Posen, S.; Zasadzinski, J. F.

    2016-08-01

    Previous work has demonstrated that the radio frequency surface resistance of niobium resonators is dramatically reduced when nitrogen impurities are dissolved as interstitial in the material. This effect is attributed to the lowering of the Mattis-Bardeen surface resistance with increasing accelerating field; however, the microscopic origin of this phenomenon is poorly understood. Meanwhile, an enhancement of the sensitivity to trapped magnetic field is typically observed for such cavities. In this paper, we conduct a systematic study on these different components contributing to the total surface resistance as a function of different levels of dissolved nitrogen, in comparison with standard surface treatments for niobium resonators. Adding these results together, we are able to show which is the optimum surface treatment that maximizes the Q-factor of superconducting niobium resonators as a function of expected trapped magnetic field in the cavity walls. These results also provide insights on the physics behind the change in the field dependence of the Mattis-Bardeen surface resistance, and of the trapped magnetic vortex induced losses in superconducting niobium resonators.

  5. Superconductivity in the metallic elements at high pressures

    NASA Astrophysics Data System (ADS)

    Hamlin, J. J.

    2015-07-01

    Although the highest superconducting critical temperature, Tc , found in an elemental solid at ambient pressure is 9.2 K (niobium), under the application of ultra-high pressures, several elements exhibit Tc values near or above 20 K. This review includes a survey of the occurrence and understanding of pressure-induced superconductivity in the subset of elements that are metallic at ambient pressure. A particular focus is directed towards those elements that display the highest superconducting critical temperatures or exhibit substantial increases in Tc with pressure. A separate article in this issue by Shimizu will cover pressure-induced superconductivity in elements that are insulating at ambient pressure.

  6. Improved method of preparing composite superconducting wire

    DOEpatents

    Verhoeven, J.D.; Gibson, E.D.; Finnemore, D.K.; Ostenson, J.E.; Schmidt, F.A.; Owen, C.V.

    1979-10-17

    An improved method of preparing composite multifilament superconducting wire of Nb/sub 3/Sn in a copper matrix eliminates the necessity of coating the drawn wire with tin. A generalized cylindrical billet of an alloy of copper containing at least 15 weight percent niobium, present in the copper as discrete, randomly distributed and oriented dendritic-shaped particles, is provided with at least one longitudinal opening which is filled with tin to form a composite drawing rod. The drawing rod is then drawn to form a ductile composite multifilament wire containing a filament of tin. The ductile wire containing the tin can then be wound into magnet coils or other devices before heating to diffuse the tin through the wire to react with the niobium forming Nb/sub 3/Sn. Also described is an improved method for making large billets of the copper-niobium alloy by consumable-arc casting.

  7. Method of preparing composite superconducting wire

    DOEpatents

    Verhoeven, John D.; Gibson, Edwin D.; Finnemore, Douglas K.; Ostenson, Jerome E.; Schmidt, Frederick A.; Owen, Charles V.

    1985-08-06

    An improved method of preparing composite multifilament superconducting wire of Nb.sub.3 Sn in a copper matrix which eliminates the necessity of coating the drawn wire with tin. A generalized cylindrical billet of an alloy of copper containing at least 15 weight percent niobium, present in the copper as discrete, randomly distributed and oriented dendritic-shaped particles, is provided with at least one longitudinal opening which is filled with tin to form a composite drawing rod. The drawing rod is then drawn to form a ductile composite multifilament wire containing a filament of tin. The ductile wire containing the tin can then be wound into magnet coils or other devices before heating to diffuse the tin through the wire to react with the niobium forming Nb.sub.3 Sn. Also described is an improved method for making large billets of the copper-niobium alloy by consumable-arc casting.

  8. Spectrophotometric determination of niobium and its application to niobium-stabilized stainless steel.

    PubMed

    Dutta, R K; Banerjee, S

    1974-10-01

    A spectrophotometric method is described for the determination of niobium by means of its reaction with tannin and thioglycollic acid. The yellow-orange colour developed with the reagent mixture at pH 4 is measured at 410-420 nm and obeys Beer's law between 0.5 and 10 ppm niobium. The method is suitable for the determination of niobium in niobium-stabilized stainless steel and other types of steels containing niobium, but a prior separation of niobium is necessary. Titanium interferes even in traces. PMID:18961571

  9. Insights to Superconducting Radio-Frequency Cavity Processing from First Principles Calculations and Spectroscopic Techniques

    SciTech Connect

    Ford, Denise Christine

    2013-03-01

    Insights to the fundamental processes that occur during the manufacturing of niobium superconducting radio-frequency (SRF) cavities are provided via analyses of density functional theory calculations and Raman, infrared, and nuclear magnetic resonance (NMR) spectra. I show that during electropolishing fluorine is bound and released by the reaction of the acid components in the solution: HF + H2SO4 <-> HFSO3 + H2O. This result implies that new recipes can possibly be developed on the principle of controlled release of fluorine by a chemical reaction. I also show that NMR or Raman spectroscopy can be used to monitor the free fluorine when polishing with the standard electropolishing recipe. Density functional theory was applied to calculate the properties of common processing impurities – hydrogen, oxygen, nitrogen, and carbon – in the niobium. These impurities lower the superconducting transition temperature of niobium, and hydride precipitates are at best weakly superconducting. I modeled several of the niobium hydride phases relevant to SRF cavities, and explain the phase changes in the niobium hydrogen system based on the charge transfer between niobium and hydrogen and the strain field inside of the niobium. I also present evidence for a niobium lattice vacancy serving as a nucleation center for hydride phase formation. In considering the other chemical impurities in niobium, I show that the absorption of oxygen into a niobium lattice vacancy is preferred over the absorption of hydrogen, which indicates that oxygen can block these phase nucleation centers. I also show that dissolved oxygen atoms can trap dissolved hydrogen atoms to prevent niobium hydride phase formation. Nitrogen and carbon were studied in less depth, but behaved similarly to oxygen. Based on these results and a literature survey, I propose a mechanism for the success of the low-temperature anneal applied to niobium SRF cavities. Finally, I

  10. Insights to Superconducting Radio-Frequency Cavity Processing from First Principles Calculations and Spectroscopic Techniques

    NASA Astrophysics Data System (ADS)

    Ford, Denise Christine

    Insights to the fundamental processes that occur during the manufacturing of niobium superconducting radio-frequency (SRF) cavities are provided via analyses of density functional theory calculations and Raman, infrared, and nuclear magnetic resonance (NMR) spectra. I show that during electropolishing fluorine is bound and released by the reaction of the acid components in the solution: HF + H2SO4 <-> HFSO3 + H2O. This result implies that new recipes can possibly be developed on the principle of controlled release of fluorine by a chemical reaction. I also show that NMR or Raman spectroscopy can be used to monitor the free fluorine when polishing with the standard electropolishing recipe. Density functional theory was applied to calculate the properties of common processing impurities---hydrogen, oxygen, nitrogen, and carbon---in the niobium. These impurities lower the superconducting transition temperature of niobium, and hydride precipitates are at best weakly superconducting. I modeled several of the niobium hydride phases relevant to SRF cavities, and explain the phase changes in the niobium hydrogen system based on the charge transfer between niobium and hydrogen and the strain field inside of the niobium. I also present evidence for a niobium lattice vacancy serving as a nucleation center for hydride phase formation. In considering the other chemical impurities in niobium, I show that the absorption of oxygen into a niobium lattice vacancy is preferred over the absorption of hydrogen, which indicates that oxygen can block these phase nucleation centers. I also show that dissolved oxygen atoms can trap dissolved hydrogen atoms to prevent niobium hydride phase formation. Nitrogen and carbon were studied in less depth, but behaved similarly to oxygen. Based on these results and a literature survey, I propose a mechanism for the success of the low-temperature anneal applied to niobium SRF cavities. Finally, I present the beginning of a model to describe magnetic