skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Overview of the RRR Nb Specifications and the Evolution of SRF Technology

Abstract

Maury Tigner’s classical review paper, “RF Superconductivity For Accelerators – Is It A Hollow Promise”# summarizes the pioneering work that was carried out from mid 1960’s to late 1070’s and is a must reading for all the new comers in to SRF world. The specifications of high purity niobium for SRF cavities seem to have evolved between 1979 and 1987. Fine grain high purity niobium has been the material of choice for SRF cavities for the past two decades. The current high RRR niobium material specifications will be reviewed from the historical context. The specification discussions include grain size, ductility, yield strength, thermal conductivity and residual resistance ratio. The effect of each of these material characteristic on the process and performance of the cavities will be explored. The recent progress on the single crystal - large grain niobium technology and its potential impact on the cost and performance of ILC cavities will be discussed. The possible relaxation of specifications, such as residual resistance ratio and Tantalum content will be presented from the perspective of reducing the cavity fabrication costs for industrial applications. Further, a summary of the low temperature mechanical properties of polycrystalline niobium will also be presented.

Authors:
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
908631
Report Number(s):
JLAB-ACC-07-624; DOE/OR/23177-0051
TRN: US0703722
DOE Contract Number:
AC05-06OR23177
Resource Type:
Conference
Resource Relation:
Conference: Fermi Lab SRF Materials Workshop, May 23, 2007, Fermilab
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 43 PARTICLE ACCELERATORS; ACCELERATORS; CAVITIES; DUCTILITY; FABRICATION; GRAIN SIZE; MECHANICAL PROPERTIES; MONOCRYSTALS; NIOBIUM; PERFORMANCE; RELAXATION; SPECIFICATIONS; SUPERCONDUCTIVITY; TANTALUM; THERMAL CONDUCTIVITY; YIELD STRENGTH

Citation Formats

G.R. Myneni. Overview of the RRR Nb Specifications and the Evolution of SRF Technology. United States: N. p., 2007. Web.
G.R. Myneni. Overview of the RRR Nb Specifications and the Evolution of SRF Technology. United States.
G.R. Myneni. Wed . "Overview of the RRR Nb Specifications and the Evolution of SRF Technology". United States. doi:. https://www.osti.gov/servlets/purl/908631.
@article{osti_908631,
title = {Overview of the RRR Nb Specifications and the Evolution of SRF Technology},
author = {G.R. Myneni},
abstractNote = {Maury Tigner’s classical review paper, “RF Superconductivity For Accelerators – Is It A Hollow Promise”# summarizes the pioneering work that was carried out from mid 1960’s to late 1070’s and is a must reading for all the new comers in to SRF world. The specifications of high purity niobium for SRF cavities seem to have evolved between 1979 and 1987. Fine grain high purity niobium has been the material of choice for SRF cavities for the past two decades. The current high RRR niobium material specifications will be reviewed from the historical context. The specification discussions include grain size, ductility, yield strength, thermal conductivity and residual resistance ratio. The effect of each of these material characteristic on the process and performance of the cavities will be explored. The recent progress on the single crystal - large grain niobium technology and its potential impact on the cost and performance of ILC cavities will be discussed. The possible relaxation of specifications, such as residual resistance ratio and Tantalum content will be presented from the perspective of reducing the cavity fabrication costs for industrial applications. Further, a summary of the low temperature mechanical properties of polycrystalline niobium will also be presented.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed May 23 00:00:00 EDT 2007},
month = {Wed May 23 00:00:00 EDT 2007}
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • We have recently demonstrated unprecedentedly high values of RRR (up to 542) in thin-films of pure Nb deposited on a-plane sapphire and MgO crystal substrates. The Nb films were grown using a vacuum arc discharge struck between a reactor grade Nb cathode rod (RRR {approx} 30) and a coaxial, semi-transparent Mo mesh anode, with a heated substrate placed just outside it. The substrates were pre-heated for several hours prior to deposition at different temperatures. Low pre-heat temperatures (<300 C) and deposition temperatures (<300 C) give low RRR (<50) films, whereas higher pre-heat (700 C) and coating temperatures (500 C) givemore » RRR=214 on a-sapphire and RRR=542 on MgO. XRD (Bragg-Brentano scans and Pole Figures), EBSD and SIMS data reveal several features: (1) on asapphire, higher temperatures show better 3D registry for epitaxial growth of Nb; the crystal structure evolves from textured, polycrystalline (with twins) to single-crystal; (2) on MgO, there is a transition from {l_brace}110{r_brace} planes to {l_brace}100{r_brace} as the temperature is increased beyond 500 C. The dramatic increase in RRR (from {approx}10 at <300 C to {approx}500 at >600 C) is correlated with better epitaxial crystal structure in both a-sapphire and MgO substrate grown films. However, the SIMS data reveal that the most important requirement for high-RRR Nb films on either substrate is the reduction of impurities in the film, especially hydrogen. The hydrogen content in the MgO grown films is 1000 times lower than in bulk Nb tested as a reference from SRF cavity grade Nb. This result has potential implications for SRF accelerators. Coating bulk Nb cavities with an MgO layer followed by our CEDTM deposited Nb films, might create superior SRF cavities that would avoid Q-slope and operate at higher peak fields.« less
  • Two strategies for improving the surface finish of niobium sheet used in superconducting radio frequency cavities were examined, using slices of single (or large-grain) material from an ingot, and equal channel angle extrusion (ECAE) preprocessing of ingot material to achieve a uniform and small grain size prior to subsequent rolling. The effect of these two processing paths on final microstructure, texture, and surface finish are discussed.
  • No abstract prepared.
  • No abstract prepared.
  • This study is an on-going research on depositing a Nb film on the internal wall of bulk Nb single cell SRF cavities, via a cathodic arc Nb plasma ions source, an coaxial energetic condensation (CED) facility at AASC company. The motivation is to firstly create a homoepitaxy-like Nb/Nb film in a scale of a ~1.5GHz RF single cell cavity. Next, through SRF measurement and materials analysis, it might reveal the baseline properties of the CED-type homoepitaxy Nb films. Literally, a top-surface layer of Nb films which sustains SRF function, always grows up in homo-epitaxy mode, on top of a Nbmore » nucleation layer. Homo-epitaxy growth of Nb must be the final stage (a crystal thickening process) of any coatings of Nb film on alternative cavity structure materials. Such knowledge of Nb-Nb homo-epitaxy is useful to create future realistic SRF cavity film coatings, such as hetero-epitaxy Nb/Cu Films, or template-layer-mitigated Nb films. One large-grain, and three fine grain bulk Nb cavities were coated. They went through cryogenic RF measurement. Preliminary results show that the Q0 of a Nb film could be as same as the pre-coated bulk Nb surface (which received a chemically-buffered polishing plus a light electro-polishing); but quality factor of two tested cavities dropped quickly. We are investigating if the severe Q-slope is caused by hydrogen incorporation before deposition, or is determined by some structural defects during Nb film growth.« less