Author: Ge, G.M.
Paper Title Page
WEPMR015 Surface Topography Techniques at Cornell University: Optical Inspection and Surface Replica 2292
 
  • G.M. Ge, F. Furuta, D. Gonnella, D.L. Hall, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, J. Sears
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Surface imperfections significantly limit the performance of superconducting radio frequency (SRF) cavities. The development of surface topography techniques aims to locate the surface flaws in an SRF cavity and profile their geometry details. This effort plays an important role of quality control in cavity productions as well as provides contour information of the defects for understanding quench mechanisms. The surface topography techniques at Cornell University include an optical inspection system and surface replica technique. In this paper, we present the details of the techniques and show features found in the SRF cavities at Cornell.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR015  
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WEPMR016 Vertical Electropolishing Studies at Cornell with KEK and Marui 2295
 
  • F. Furuta, G.M. Ge, T. Gruber, J.J. Kaufman, J. Sears
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • H. Hayano, S. Kato, T. Saeki
    KEK, Ibaraki, Japan
 
  Cornell's SRF group has developed Vertical Electro-Polishing (VEP) and applied on 1.3GHz Niobium SRF cavities as the primary surface treatment. High-Q and high voltage performances of VEP'ed SRF cavities had been successfully demonstrated at Cornell. In 2014, new VEP R&D collaboration has started between Cornell, KEK, and Marui Galvanizing Co. Ltd. (MGI). MGI and KEK has developed their original VEP cathode named 'i-cathode Ninja'® which has four retractable wing-shape parts per cell for single-/9-cell cavities. We will report the results of VEP process using 'i-cathode Ninja'® on single cell cavity at Cornell.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR016  
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WEPMR018 Time Resolved Cryogenic Cooling Analysis of the Cornell Injector Cryomodule 2298
 
  • R.G. Eichhorn, A.C. Bartnik, B.M. Dunham, G.M. Ge, G.H. Hoffstaetter, H. Lee, M. Liepe, S.R. Markham, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  To demonstrate key parameters of a an energy recovery linac (ERL) at Cornel, an injector based on a photo gun and an SRF cryomodule was designed and built. The goal was to demonstrate high current generation while achieving low emittances. While the emittance goal has been reached, the current achieved so far is 75 mA. Even though this is a world record, it is still below the targeted 100 mA. While ramping up the current we observed excessive heating in the fundamental power coupler which we were able to track down to insufficient cooling of the 80 K intercepts. These intercepts are cooled by a stream of parallel cryogenic flows which we found to be unbalanced. In this paper we will review the finding, describe the analysis we did, modeling of the parallel flow and the modifications made to the module to overcome the heating.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR018  
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WEPMR019 Development of Plasma Cleaning at Cornell University 2302
 
  • G.M. Ge, F. Furuta, M. Liepe, V. Veshcherevich
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Cornell University is developing the plasma cleaning technology as an alternative cleaning technique for SRF cavity surface preparation. In experiments, we successfully ignited the plasma in a single-cell SRF cavity. However the experiments were limited by the peak electric-fields in the RF coupler. In this paper, we show the analysis of the limitation and propose a new design of the coupler which can eliminate the limitation.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR019  
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WEPMR020 First Cool-down of the Cornell ERL Main Linac Cryo-Module 2305
 
  • R.G. Eichhorn, J.V. Conway, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Cornell University has finished building a 10 m long superconducting accelerator module as a prototype of the main linac of a proposed ERL facility. This module houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode with a design field of 16 MV/m and a Quality factor of 2x1010. We wil shortly review the design and focus on reporting on the first cool-down of this module. We will giving data for various cool-down scenarios (fast/ slow), uniformity and performance  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR020  
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WEPMR021 HOM Measurements for Cornell's High-current CW ERL Cryomodule 2309
 
  • F. Furuta, R.G. Eichhorn, G.M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, P. Quigley, V. Veshcherevich
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  The main linac cryomodule (MLC) for the future energy-recovery linac (ERL) based synchrotron-light facility at Cornell had been designed, fabricated, and tested. It houses 6 SRF cavities with individual higher order-modes (HOMs)absorbers and one magnet/ BPM section. We will report the HOM study on MLC.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR021  
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WEPMR022 ERL Main Linac Cryomodule Cavity Performance and Effect of Thermal Cycling 2312
 
  • F. Furuta, J. Dobbins, R.G. Eichhorn, G.M. Ge, D. Gonnella, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Cornell has designed, fabricated, and tested a high current (100 mA) CW SRF prototype cryomodule for the future energy-recovery linac (ERL) based synchrotron-light facility at Cornell . It houses six 7-cell SRF cavities with individual HOM absorbers and one magnet/ BPM section. Cavities are targeted to operate with high Qo of 2.0·1010 at 16.2 MV/m, 1.8 K in continuous wave (CW) mode. We will report the RF test results of 7-cell cavities in this cryomodule after initial cooldown and several thermal cycles with different cooldown method.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR022  
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WEPMR025 Improved N-Doping Protocols for SRF Cavities 2323
 
  • D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: NSF, DOE
Nitrogen-doping has been shown to consistently produce better quality factors in SRF cavities than is achievable with standard preparation techniques. Unfortunately, nitrogen-doping typically brings with it lower quench fields and higher sensitivities of residual resistance to trapped magnetic flux. Here we present work to understand these effects in hopes of mitigating them while maintaining the high Q desired by future projects. Using a nitrogen diffusion simulation, material parameters of nitrogen-doped cavities can be predicted prior to doping. These simulations results are consistent with SIMS data taken from samples treated with cavities. The nature of doping's effect on quench field has also been studied using CW and pulsed measurements. These results have allowed us to better understand the nature of nitrogen-doping and its effect on cavity performance.
 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR025  
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WEPMR027 Dependence of Surface Resistance on N-Doping Level 2331
 
  • D. Gonnella, F. Furuta, G.M. Ge, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: NSF, DOE
Nitrogen-doping has become a standard tool for reaching high quality factors in SRF cavities in the medium field region at 2 K. This high Q has been shown to be a result of lowering of the temperature dependent BCS resistance. Here we show that this lowering of the BCS resistance is due to interstitial nitrogen in the niobium lowering the mean free path. The BCS resistance extracted from experimental data is shown to be consistent with theoretical predictions from BCS theory; that there is an optimal doping of which the mean free path is lowered to about half the intrinsic coherence length. These results provide insight into understanding the mechanisms behind nitrogen-doping and allow us to more accurately predict doping parameters to reach optimal cavity performance.
 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR027  
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THOBB02 Impurity Doping of Superconducting Radio Frequency Cavities 3195
SUPSS093   use link to see paper's listing under its alternate paper code  
 
  • P.N. Koufalis, F. Furuta, G.M. Ge, D. Gonnella, J.J. Kaufman, M. Liepe, J.T. Maniscalco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: NSF PHYS-1416318
Impurity doping of bulk-niobium superconducting radio frequency (SRF) cavities is a relatively new field of study and the underlying physics is not yet fully understood. Previous studies have shown an increase in the intrinsic quality factor and the corresponding decrease of the temperature-dependent component of the surface resistance of nitrogen-doped cavities with increasing accelerating field.* Here we investigate the effects of alternative inert dopants on the surface resistance and thus the intrinsic quality factor of SRF cavities in pursuit of the optimal dopant and doping level.
A. Grassellino et al., Nitrogen and Argon Doping of Niobium for Superconducting Radio Frequency Cavities. Supercond. Sci. Technol., 26(102001), 2013
 
slides icon Slides THOBB02 [4.048 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THOBB02  
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