Fundamental R&D - Nb
field-dependence
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TUFUA1 The Field-Dependent Surface Resistance of Doped Niobium: New Experimental and Theoretical Results 340
 
  • J.T. Maniscalco, M. Ge, P.N. Koufalis, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • T. Arias, D. Liarte, J.P. Sethna, N. Sitaraman
    Cornell University, Ithaca, New York, USA
 
  We present systematic work investigating how different doping and post-doping treatments affect the BCS surface resistance at 1.3~GHz and higher frequencies. We examine the field-dependent BCS resistance at many temperatures as well as the field-dependent residual resistance and use the results to reveal how impurity species and concentration levels affect the field-dependent RF properties. We further demonstrate the importance of thermal effects and their direct dependence on doping level. We use the tools of Density Functional Theory to work towards an {\em ab initio} model of electron overheating to theoretically confirm the impact of doping, create a full model that includes thermal effects to predict the field dependent resistance, and show that the predictions of the model agree with results from doped and non-doped cavities ({\em e.g.} the strength of the anti-Q-slope and the high-field Q slope). Finally, we use our experimental results to systematically assess and compare theories of the field-dependent BCS resistance, showing that the current theory on smearing of the density of states is incomplete.  
slides icon Slides TUFUA1 [6.780 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA1  
About • paper received ※ 01 July 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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TUFUB2
New Insights into RF Field Amplitude and Frequency Dependence of Vortex Surface Resistance  
 
  • M. Checchin
    Fermilab, Batavia, Illinois, USA
 
  In this talk, the surface resistance due to trapped vortices is being described. Experimental data acquired at Fermilab for bulk niobium elliptical cavities as a function of frequency, trapped magnetic field value and RF field amplitude will be presented. Numerical calculations of the vortex dynamics under RF drive will be also presented in order to describe the mechanism underneath the RF field amplitude dependence of the surface resistance due to trapped vortices. Different pinning landscapes in the material will be taken into consideration, aiming to pinpoint the pinning configuration that better describes the observed field dependence.  
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TUFUB7 Measurement of Surface Resistance Properties with Coaxial Resonators - Review 374
 
  • H. Park, S.U. De Silva, J.R. Delayen
    ODU, Norfolk, Virginia, USA
 
  Achieving ever decreasing surface resistance at higher field in superconducting RF accelerating structures is one of most outstanding developments in modern accelerators. The BCS theory has been used widely to estimate the surface resistance and to direct the technology. However, recent research results show that the behavior of the surface resistance further deviates from the BCS theory. So far the study on surface resistance was performed usually with cavities of single frequency which limited the study of frequency dependent surface resistance. The Center for Accelerator Science at Old Dominion University has designed and built several half wave coaxial cavities to study the frequency, temperature, and RF field dependence of surface resistance. TRIUMF in Canada also joined this line of research using such multi frequency quarter wave and half wave coaxial cavities. This type of multi mode cavity will allow us to systematically study the parameters affecting surface resistance on the same cavity surface. In this paper, we review the results ODU and TRIUMF collected so far and proper analysis methods.  
slides icon Slides TUFUB7 [3.551 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB7  
About • paper received ※ 01 July 2019       paper accepted ※ 12 July 2019       issue date ※ 14 August 2019  
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TUP046 Low Frequency, Low Beta Cavity Performance Improvement Studies 527
 
  • P. Kolb, R.E. Laxdal, Z.Y. Yao
    TRIUMF, Vancouver, Canada
 
  In recent years, new discoveries such as N2 doping and infusion lead to a significant increases in Q0 and accelerating gradient for 1.3 GHz, β=1 elliptical cavities. To understand and to adapt these treatments for lower frequency, \beta < 1 cavities, two coaxial test cavities, one quarter-wave resonator (QWR) and one half-wave resonator (HWR), have been built and put through a systematic study of these new treatments to show the effectiveness of these treatments at different frequencies. These cavities are tested in their fundamental mode and several higher order modes to study the frequency dependence of new cavity treatments such as N2 doping and infusion. Results of these studies are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP046  
About • paper received ※ 22 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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TUP049 Maximum Performance of Cavities Affected by the High-field Q-slope (HFQS) 533
 
  • G. Ciovati
    JLab, Newport News, Virginia, USA
  • A.V. Gurevich, I.P. Parajuli
    ODU, Norfolk, Virginia, USA
 
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The work of I. P. and A. G. is supported by NSF Grant PHY 100614-010.
The performance of high-purity, bulk niobium SRF cavities treated by chemical processes such as BCP or EP is limited by the so-called high-field Q-slope (HFQS). Several models and experimental studies have been proposed and performed over the years to understand the origin of these anomalous losses but a general consensus on what these orgins are is yet to be established. In this contribution, we present the results from the RF tests of several 1.3 GHz single-cell cavities limited by the HFQS and tested using a variable input coupler. This allowed to maintain close to critical coupling even at high field and the data showed that the HFQS did not saturate and that in some cases a power dissipation of up to 200 W at 2 K could be sustained without quench.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP049  
About • paper received ※ 21 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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TUP051 Progress Towards Commissioning the Cornell DC Field Dependence Cavity 543
SUSP014   use link to see paper's listing under its alternate paper code  
 
  • J.T. Maniscalco, T. Gruber, A.T. Holic, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  The Cornell DC Field Dependence Cavity is a new coaxial test resonator designed to study the impact of strong (up to 200 mT or more) DC surface magnetic fields on the superconducting surface resistance, providing physical insight into the root of the ‘‘anti-Q-slope’’ and probing critical fields. In this report we report progress in the commissioning of this new apparatus, including finalized design elements and results of prototype tests.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP051  
About • paper received ※ 25 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THFUB5
Employing SRF to Boost Coherence of 3D Quantum Systems  
 
  • A.S. Romanenko
    Fermilab, Batavia, Illinois, USA
 
  Superconducting quantum systems are currently at the leading edge of quantum information science (QIS), including quantum computing, as well as fundamental quantum physics experiments and particle physics search experiments. So far though the 3D superconducting cavities which were used in the field of QIS, had quality factors Q ~108, providing one of the primary limitations for the achievable useful quantum superposition (aka coherence) times. In this talk I will overview how the SRF expertise can bring the field of QIS ahead by several orders of magnitude in coherence times, as well discuss the emerging Quantum Technology effort at Fermilab and the first record achievements in this area.  
slides icon Slides THFUB5 [9.583 MB]  
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