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CERN Document Server 14 записей найдено  1 - 10следующий  перейти к записи: Поиск длился 0.64 секунд. 
1.
Magnetic Field Penetration of Niobium Thin Films Produced by the ARIES Collaboration / Turner, Daniel (Cockcroft Inst. Accel. Sci. Tech. ; Lancaster U. (main)) ; Burt, Graeme (Cockcroft Inst. Accel. Sci. Tech. ; Lancaster U. (main)) ; Chyhyrynets, Eduard (INFN, Legnaro) ; Dumbell, Keith (Cockcroft Inst. Accel. Sci. Tech. ; Daresbury) ; Junginger, Tobias (TRIUMF ; U. Victoria (main)) ; Leith, Stewart (U. Siegen (main)) ; Malyshev, Oleg (Daresbury ; Cockcroft Inst. Accel. Sci. Tech.) ; Medvids, Arturs (Riga Tech. U.) ; Onufrijevs, Pavels (Riga Tech. U.) ; Pira, Cristian (INFN, Legnaro) et al.
Superconducting (SC) thin film coatings on Cu substrates are already widely used as an alternative to bulk Nb SRF structures. Using Cu allows improved thermal stability compared to Nb due to having a greater thermal conductivity. [...]
2022 - 5 p. - Published in : JACoW SRF 2021 (2022) 77-81 Fulltext: PDF;
In : 20th International Conference on RF Superconductivity (SRF 2021), Online, US, 28 Jun - 2 Jul 2021, pp.77-81
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2.
High Frequency Nonlinear Response of Superconducting Cavity-Grade Nb surfaces / Oripov, Bakhrom (Maryland U.) ; Bieler, Thomas (Michigan State U.) ; Ciovati, Gianluigi (Jefferson Lab) ; Calatroni, Sergio (CERN) ; Dhakal, Pashupati (Jefferson Lab) ; Junginger, Tobias (Lancaster U. (main)) ; Malyshev, Oleg B. (Daresbury) ; Terenziani, Giovanni (CERN) ; Valente-Feliciano, Anne-Marie (Jefferson Lab) ; Valizadeh, Reza (Daresbury) et al.
Nb superconducting radio-frequency (SRF) cavities are observed to break down and lose their high-Q superconducting properties at accelerating gradients below the limits imposed by theory. The microscopic origins of SRF cavity breakdown are still a matter of some debate. [...]
arXiv:1904.07432.- 2019-06-13 - 9 p. - Published in : Phys. Rev. Applied 11 (2019) 064030 Fulltext: PDF;
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3.
A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities / Junginger, Tobias (Helmholtz-Zentrum, Berlin ; Lancaster U. (main) ; Cockcroft Inst. Accel. Sci. Tech.) ; Calatroni, S. (CERN) ; Sublet, A. (CERN) ; Terenziani, G. (CERN) ; Prokscha, T. (PSI, Villigen) ; Salman, Z. (PSI, Villigen) ; Suter, A. (PSI, Villigen) ; Proslier, T. (Argonne) ; Zasadzinski, J. (IIT, Chicago)
Point contact tunneling (PCT) and low energy muon spin rotation (LE-muSR) are used to probe, on the same samples, the surface superconducting properties of micrometer thick niobium films deposited onto copper substrates using different sputtereing techniques: diode, dc magnetron (dcMS) and HIPIMS. The combined results are compared to radio-frequency tests performances of RF cavities made with the same processes. [...]
arXiv:1703.08635.- 2017-11-07 - 14 p. - Published in : Supercond. Sci. Technol. 30 (2017) 125013 Fulltext: PDF; External links: 00002 Scanning electron microscope (SEM) images of the three samples used for the point contact tunneling measurements.; 00011 Asymmetry function versus time at \unit[50]{K} for the HIPIMS sample in a longitudinal field of 0,2 and 10 mT.; 00004 Surface resistance $R\msub{S}$ as a function of peak surface magnetic field $B\msub{p}$ for two quarter wave cavities at \unit[4.2]{K}.; 00007 (a) Example of conductance curves displaying the zero bias conductance peak obtained on the HIPIMS sample, the curves are shifted by 0.25 for more clarity.; 00001 Top: Schematics of the \unit[1.3]{GHz} sputtering setup as used to produce the dcMS and HIPIMS samples. The samples are located at the equator, the region of largest diameter. Bottom: Position of the HIE-ISOLDE Nb/Cu samples i9 and Tbi taken from the mock-up cavity for PCT and LE-$\mu$SR measurements respectively.; 00013 Asymmetry function of muons stooped in an N$_2$-overlayer on top of the HIPIMS sample.; 00010 Asymmetry functions obtained at zero field and $T\approx$\unit[3.5]{K} for the HIPIMS sample at the surface and the dcMS sample at about \unit[100]{nm} depth. The HIPIMS sample shows strong signs of muon dynamics possibly related to surface magnetism. The asymmetry function of the dcMS sample recovers to about 1/3 of its initial value, which signifies that each muon experiences a static magnetic field, while the fields seen by different muons are randomly distributed.; 00003 Surface resistance $R\msub{S}$ as a function of peak surface magnetic field $B\msub{p}$ for three thin film cavities.; 00005 Surface resistance $R\msub{S}$ as a function of peak surface magnetic field $B\msub{p}$ for three elliptical cavities.; 00000 Top: Schematics of the \unit[1.3]{GHz} sputtering setup as used to produce the dcMS and HIPIMS samples. The samples are located at the equator, the region of largest diameter. Bottom: Position of the HIE-ISOLDE Nb/Cu samples i9 and Tbi taken from the mock-up cavity for PCT and LE-$\mu$SR measurements respectively.; 00008 Penetration of the magnetic field in three Nb/Cu samples at $T\approx$\unit[3.5]{K}; 00014 Stopping profiles of muons in niobium of different energy calculated with the TRIM.SP software.; 00009 Penetration depth change measured on a \unit[1.3]{GHz} HIPIMS cavity as a function of $f(T)=1/\sqrt{1-(\frac{T}{T\msub{c}})^4}-1$ \cite{Junginger_PRSTAB_2015}.; 00015 Asymmetry function of muons stopped on a N$_2$ layer grown on a Ni plate.; 00012 Hop rate $\nu$ as a function of temperature for the HIPIMS sample. The line is a guide to the eye.; 00006 Summary of the PCTS measurement performed on 3 niobium samples deposited on Cu substrate with 3 different deposition methods; (a) HIPIMS, (b) standard DC magnetron sputtering or dcMS and (c) diode sputtering. For each sample, 80 to 100 junctions were measured. A set of about 10 representative normalized tunneling conductance curves are represented on the left (shifted by 0.25 for more clarity). The statistics of the superconducting gap $\Delta$ and inelastic parameter $\Gamma/\Delta$ as extracted from the fits are displayed in the middle. The temperature dependence of a characteristic tunnel junction is shown on the right with the corresponding temperature dependence of $\Delta$. (d) Example of conductance spectrum shifted by 0.25 that show no hint of superconductivity and considered as normal metal junctions $\Delta$ = 0 meV. (e) Example of tunnel junction showing very peculiar background for V$\ge\Delta$, the curves have been shifted by 1 for more clarity.
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4.
Diagnostic developments at CERN’s SRF testing facility / Macpherson, Alick (CERN) ; Aull, Sarah (CERN) ; Benoit, Antoine (CERN) ; Fernández López, Pablo (CERN) ; Hernández-Chahín, Karim (Mexico, ININ ; CERN) ; Jarrige, Christophe (CERN) ; Junginger, Tobias (Helmholtz-Zentrum, Berlin ; Alberta U. ; TRIUMF) ; Maesen, Pierre (CERN) ; Schirm, Karl (CERN) ; Torres-Sanchez, Roberto (CERN) et al.
As part of CERN’s re-establishment of an SRF cold testing facility for bulk niobium cavities, diagnostic instrumentation and testing procedures on our vertical cryostat have been upgraded, with particular attention given to quench location, ambient magnetic field control, thermometry and thermal cycling techniques. In addition, preparation and measurement procedures have been addressed, allowing for improved measurement of cavity properties and detailed study of transient effects during the course of cavity testing..
2015 - 5 p. - Published in : 10.18429/JACoW-SRF2015-TUPB080 Fulltext: PDF;
In : 17th International Conference on RF Superconductivity, Whistler, Canada, 13 - 18 Sep 2015, pp.TUPB080
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5.
Secondary electron yield of SRF materials / Aull, Sarah (CERN ; Siegen U.) ; Junginger, Tobias (CERN) ; Knobloch, Jens (Helmholtz-Zentrum, Berlin ; Siegen U.) ; Neupert, Holger (CERN)
The secondary electron yield (SEY) describes the number of electrons emitted to the vacuum per arriving electron at the surface. For a given geometry, the SEY is the defining factor for multipacting activity. [...]
2015 - 5 p. - Published in : 10.18429/JACoW-SRF2015-TUPB050 Fulltext: PDF;
In : 17th International Conference on RF Superconductivity, Whistler, Canada, 13 - 18 Sep 2015, pp.TUPB050
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6.
Low energy muon spin rotation and point contact tunneling applied to niobium films for SRF cavities / Junginger, Tobias (Alberta U. ; TRIUMF) ; Calatroni, Sergio (CERN) ; Prokscha, Thomas (PSI, Villigen) ; Proslier, Thomas (Argonne (main)) ; Salman, Zaher (PSI, Villigen) ; Suter, Andreas (PSI, Villigen) ; Terenziani, Giovanni (CERN ; Sheffield U.) ; Zasadzinski, John (IIT, Chicago (main))
Muon spin rotation (muSR) and point contact tunneling (PCT) are used since several years for bulk niobium studies. Here we present studies on niobium thin film samples of different deposition techniques (diode, magnetron and HIPIMS) and compare the results with RF measurements and bulk niobium results. [...]
2015 - 5 p. - Published in : 10.18429/JACoW-SRF2015-TUPB042 Fulltext: PDF;
In : 17th International Conference on RF Superconductivity, Whistler, Canada, 13 - 18 Sep 2015, pp.TUPB042
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7.
On the understanding of Q-slope of niobium thin films / Aull, Sarah (CERN) ; Junginger, Tobias (CERN) ; Knobloch, Jens (Helmholtz-Zentrum, Berlin ; Siegen U.) ; Sublet, Alban (CERN) ; Valente-Feliciano, Anne-Marie (Jefferson Lab) ; Venturini Delsolaro, Walter (CERN) ; Zhang, Pei (CERN)
The Q-slope of niobium coated copper cavities at medium fields is still the limiting factor for the application the Nb/Cu technology in accelerators. This paper presents a dedicated study of a niobium coating with bulk-like characteristics which shows a Q-slope comparable to bulk Nb at 400 MHz and 4 K. [...]
2015 - 7 p. - Published in : 10.18429/JACoW-SRF2015-TUBA03 Fulltext: PDF;
In : 17th International Conference on RF Superconductivity, Whistler, Canada, 13 - 18 Sep 2015, pp.TUBA03
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8.
High flux three dimensional heat transport in superfluid helium and its application to a trilateration algorithm for quench localization with OSTs / Junginger, Tobias (Alberta U. ; TRIUMF) ; Horn, Phillipp (Dresden, Tech. U.) ; Koettig, Torsten (CERN) ; Liao, Kitty (CERN) ; Macpherson, Alick (CERN) ; Peters, Benedikt (KIT, Karlsruhe)
Oscillating superleak transducers of second sound can be used to localize quench spots on superconducting cavities by trilateration. However propagation speeds faster than the velocity of second sound are usually observed imped- ing the localization. [...]
2015 - 4 p. - Published in : 10.18429/JACoW-SRF2015-MOPB049 Fulltext: PDF;
In : 17th International Conference on RF Superconductivity, Whistler, Canada, 13 - 18 Sep 2015, pp.MOPB049
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9.
Measurement Report for the Four-Rod LHC Crab Cavity. Cold Tests held in July 2014 / Navarro Tapia, Maria (CERN) ; Burt, G (The Cockcroft Institute, Lancaster University, Daresbury, United Kingdom) ; Calaga, Rama (CERN) ; Hernandez Chahin, Karim Gibran (Universidad de Guanajuato (MX)) ; Junginger, Tobias (CERN) ; Macpherson, Alick (CERN) ; Torres-Sanchez, Roberto (CERN)
The performance of the four-rod cavity prototype considered for the HL-LHC upgrade has already been assessed at CERN at cryogenic temperatures three times in the last two years [1, 2, 3]. [...]
CERN-ACC-NOTE-2015-0016. - 2015. - 15 p.
Full text
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10.
Experimental evidence for electric surface resistance in niobium / Junginger, Tobias (Helmholtz-Zentrum, Berlin) ; Aull, Sarah (CERN) ; Weingarten, Wolfgang (CERN) ; Welsch, Carsten Peter (Liverpool U.)
Identifying the loss mechanisms of niobium cavities enables an accurate determination of applications for future accelerator projects and points to research topics required to mitigate current limitations. For several cavities an increasing surface resistance above a threshold field, saturating at higher field has been observed. [...]
arXiv:1302.2802.- 2017-08-17 - 7 p. - Published in : IEEE Trans. Appl. Supercond. 27 (2017) 3500607 Fulltext: PDF; External links: 00001 Surface resistance of an elliptical \unit[1300]{MHz} bulk niobium cavity at \unit[2]{K}. Data taken by Romanenko et al. \cite{Romanenko2013}; 00000 Schematic view of energy states at thermal equilibrium near the interface of superconducting niobium and niobium-pentoxide Nb2O5; (left) after exposure to a positive and (right) to a negative electric field $E_\bot$. Note that the population of occupied electron states in Nb$_2$O$_2$ is modified after the exposure of the electric field which indicates current flow. The degree of half-toning indicates the density of states. E$_F$ is the Fermi energy and $\Delta$ is the energy gap of superconducting niobium.; 00002 Surface resistance $R\msub{S}$ of a niobium film sample tested with Quadrupole Resonator at \unit[400]{MHz} (\unit[2.5]{K} (blue), \unit[4]{K} (magenta)) and \unit[800]{MHz} (\unit[2.5]{K} (black), \unit[4]{K} (red). $R\msub{S}$ was obtained under the assumption that all losses are solely caused by the surface magnetic field.; 00003 Electric surface resistance at \unit[400]{MHz} (\unit[2.5]{K} (blue), \unit[4]{K} (magenta)) and \unit[800]{MHz} (\unit[2.5]{K} (black), \unit[4]{K} (red)) of a niobium film sample. The lines show predictions from a collective least squares multiparameter fit to a data set comprising 183 values $R\msub{S}(f,T,E)$. The data dsiplayed is the same as in Fig. \ref{figure:RB_NbCU} without losses independent on field strength. These were subtracted from each curve. All field dependent losses are assumed to be caused by the surface electric field.
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