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Title: Niobium Specifications and Performance of SRF Cavities

Abstract

No abstract prepared.

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
899628
Report Number(s):
JLAB-ACP-07-610; DOE/OR/23177-0026
TRN: US0702067
DOE Contract Number:
AC05-06OR23177
Resource Type:
Conference
Resource Relation:
Conference: APAC 2007 SRF Mini Workshop, Indore, India, January 28, 2007
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; SUPERCONDUCTING CAVITY RESONATORS; NIOBIUM; PERFORMANCE; SPECIFICATIONS

Citation Formats

Ganapati Rao Myneni, Peter Kneisel, Tadeau Carneiro, Richard Ricker, T. G-Herold, Frank Stevie, Phillip Russell, Xenia Singer, Waldemar Singer, Bill Lanford, Björgvin Hjörvarsson, Sean Agnew, B. Shivaram, and Sindhunil Roy. Niobium Specifications and Performance of SRF Cavities. United States: N. p., 2007. Web.
Ganapati Rao Myneni, Peter Kneisel, Tadeau Carneiro, Richard Ricker, T. G-Herold, Frank Stevie, Phillip Russell, Xenia Singer, Waldemar Singer, Bill Lanford, Björgvin Hjörvarsson, Sean Agnew, B. Shivaram, & Sindhunil Roy. Niobium Specifications and Performance of SRF Cavities. United States.
Ganapati Rao Myneni, Peter Kneisel, Tadeau Carneiro, Richard Ricker, T. G-Herold, Frank Stevie, Phillip Russell, Xenia Singer, Waldemar Singer, Bill Lanford, Björgvin Hjörvarsson, Sean Agnew, B. Shivaram, and Sindhunil Roy. Sun . "Niobium Specifications and Performance of SRF Cavities". United States. doi:. https://www.osti.gov/servlets/purl/899628.
@article{osti_899628,
title = {Niobium Specifications and Performance of SRF Cavities},
author = {Ganapati Rao Myneni and Peter Kneisel and Tadeau Carneiro and Richard Ricker and T. G-Herold and Frank Stevie and Phillip Russell and Xenia Singer and Waldemar Singer and Bill Lanford and Björgvin Hjörvarsson and Sean Agnew and B. Shivaram and Sindhunil Roy},
abstractNote = {No abstract prepared.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 28 00:00:00 EST 2007},
month = {Sun Jan 28 00:00:00 EST 2007}
}

Conference:
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  • Recent incorporation of analytic electrochemistry into the development of protocols for electropolishing niobium SRF cavities has yielded new insights for optimizing this process for consistent, high-performance results. Use of reference electrodes in the electrolyte, electrochemical impedance spectroscopy (EIS), rotating disk electrodes (RDE), and controlled sample temperatures has greatly clarified the process dynamics over the empirical understanding developed via years of practice. Minimizing RF losses at high operational gradients is very valuable for CW linacs. Jefferson Lab is applying these new insights to the low-loss 7-cell cavity design developed for the CEBAF 12 GeV Upgrade. Together with controlled cleaning and assemblymore » techniques to guard against field-emission-causing particulates, the resulting process is yielding consistent cavity performance that exceeds project requirements. Cavity tests show BCS-limited Q well above 30 MV/m. Detailed process data, interpretation, and resulting rf performance data will be presented.« less
  • Two types of electric discharges were used to demonstrate the validity of plasma surface treatment for superconducting radio-frequency (SRF) cavities. The experiments were performed on disc-shaped Nb samples and compared with identical samples treated with buffer chemical polishing (BCP) techniques. Surface analysis indicates comparable or superior properties of plasma-treated samples. These promising results are still preliminary and additional work is in progress.
  • In the framework of SRF cavity development, Fermilab is creating the infrastructure needed for the characterization of the material used in the cavity fabrication. An important step in the characterization of ''as received'' niobium sheets is eddy current scanning. Eddy current scanning is a non-destructive technique first adopted and further developed by DESY with the purpose of checking the cavity material for subsurface defects and inclusions. Fermilab has received and further upgraded a commercial eddy current scanner previously used for the SNS project. This scanner is now used daily to scan the niobium sheets for the Fermilab third harmonic, themore » ILC, and the Proton Driver cavities. After optical inspection, more than 400 squares and disks have been scanned and when necessary checked at the optical and electron microscopes, anodized, or measured with profilometers looking for surface imperfections that might limit the performance of the cavities. This paper gives a status report on the scanning results obtained so far, including a discussion of the classification of signals being detected.« less
  • This work investigates properties of large grained, high purity niobium with respect to the forming of superconducting radio frequency (SRF) cavities from such large grained sheets. The yield stresses were examined using tensile specimens that were essentially single crystals in orientations evenly distributed in the standard projection triangle. No distinct yield anisotropy was found, however, vacuum annealing increased the yield strength by a factor 2..3. The deep drawing forming operation of the half cells raises the issues of elastic shape changes after the release of the forming tool (springback) and residual stresses, both of which are indicated to be negligible.more » This is a consequence of the low yield stress (< 100 MPa) and the large thickness (compared to typical thicknesses in sheet metal forming). However, the significant anisotropy of the transversal plastic strains after uniaxial deformation points to potentially critical thickness variations for large grained / single crystal half cells, thus raising the issue of controlling grain orientation or using single crystal sheet material.« less
  • Currently available technology can only inspect flat sheets and allow the elimination of defective flat sheets before the expensive forming and machining of the SRF cavity half-cells, but it does not eliminate the problem of remaining or uncovered surface impurities after partial chemical etching of the half-cells, nor does it detect any defects that may have been added during the fabrication of the half-cells. AMAC has developed a SQUID scanning system based on eddy current technique that allows the scanning of curved Nb samples that are welded to make superconducting RF cavity half-cells. AMAC SQUID scanning system successfully located themore » defects (Ta macro particles about 100 mm diameter) in a flat Nb sample (top side) and was able to also locate the defects in a cylindrical surface sample (top side). It is more significant that the system successfully located the defects on the backside of the flat sample and curved sample or 3-mm from the top surface. The 3-D SQUID-based Nondestructive instrument will be further optimized and improved in making SRF cavities and allow inspection and detection during cavity manufacturing for achieving highest accelarating fields.« less