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Thomas Jefferson National Accelerator FacilityOperated by the Southeastern Universities Research Association for the U.S. Department of Energy
Physical and Mechanical Properties of Single and Large Crystal High-RRR niobium
Ganapati Rao Myneni
SRF 2005 WorkshopCornell University
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 2
Collaborators
Peter Kneisel, Gigi Ciovati JLAB
Tadeu Carneiro CBMM/Reference Metals
Fred Stevie NCSU
Richard Ricker, Rick Paul NIST
Xenia & Waldemar Singer DESY
Bill Lanford UNY Albany
Björgvin Hjörvarsson Uppsala University
Sean Agnew, B. Shivaram UVa
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 3
Introduction
• SNS Cavity RRR Niobium Issues
• Hydrogen Workshop November 2002 (ISOHIM)
• Niobium Consortium Formation
• Reference Metals/CBMM CRADA
• Single/Large Grain Niobium Developments
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 4
Types of high RRR bulk niobium
1. Polycrystalline niobium from standard process including rolling & recrystalization
No apparent control on the microstructure, texture andHeterogeneity
2. High Tantalum content RRR niobium is available at reduced costMeasurements indicate 1300 ppm Ta cavity reaches Eacc ~ 30 MV/m
3. Single/large crystal ingots with required orientation
One obtains the discs directly form slicing of the ingots, reduced process steps leading to lower costs and potentially very good performance
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 5
What Do We Know About RRR Nb
• We like to have highest RRR (Thermal Conductivity for Thermal Stability) @4.3 K Spec.
• 30 – 40 % Percentage of Elongation for forming the half cells
• We specify certain Yield Strength• We have Specifications for impurity content (But
can’t Verify with the available techniques)• We have no control on the major properties of RRR
Nb as produced today in the form of sheets• So there are opportunities to optimize these
properties
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 6
20' 600' 700' 750' 800'0
100
200
300
400
N
G
rain
siz
e (µ
m)
Temperature (C)
K
P
Lineal intercept grain size as a function of annealing temperature for the three lots of high-purity niobium
UVa Measurements
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 7
Relationship between RRR and interstitial impurities of Niobium
0
10
20
30
40
50
60
70
80
0 50 100 150 200 250 300 350 400RRR
Inte
rstit
ial i
mpu
ritie
s co
ncen
tratio
n [w
t ppm
ONHC
Interstitials vs RRR (Tokyo Denkai)
NCSU
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 8
0
100
200
300
400
500
600
700
800
0 10 20 30 40 50 60 70
Percentage of elongation
load
(Pou
nds)
AS1161A RRR~180HT1161AAS1162A RRR~170HT1162AAS1163A RRR~150HT1163AAS1164A RRR~150HT1164A
Effect of Tantalum on Mechanical Properties
Optimum Ta 600 – 1000 ppm
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 9
Large Grain RRR Niobium
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 10
Single Crystal Niobium
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 11
Reference Metals RRR Nb from Ingot
0
100
200
300
400
500
600
0 10 20 30 40 50 60 70 80 90 100
Percentage of elongation
Load
(Pou
nds)
RMCIRRR3RMCIRRR4RMCIRRR5RMCIRRR7RMCIRRR6RMCIRRR8RMCIRRR1RMCIRRR2
0
2
4
6
8
10
12
14
16
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014
Strain
Stre
ss (K
SI)
RMCIRRR3
RMCIRRR4
RMCIRRR5
RMCIRRR7
RMCIRRR6
RMCIRRR8
RMCIRRR1
RMCIRRR2
RRR Nb from Ingot
Ta ~ 800 ppm, RRR ~ 280
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 12
Polycrystalline RRR niobium
SNS high RRR niobium
0
2
4
6
8
10
12
14
16
18
0 0.002 0.004 0.006 0.008 0.01 0.012
Strain
Stre
ss (K
SI)
WCASR
WC8006
WC80062
WC6006
WC7006
WC8001
WCASR1
WCL60010
WC8003
WC7501.5
Elastic Modulus ~110 GPa
Damage layer ~ 200 to 300 microns
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 13
Large Crystal RRR Niobium
RMS Surface Roughness 27 nm per A. WU/JLAB on a 0.2 X 0.2 mm area
After ~ 80 micron BCP 1:1:2
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 14
Single Crystal RRR niobium
0
100
200
300
400
500
600
0 20 40 60 80 100 120
Percentage of Elongation
Load
(Pou
nds)
NIST1 SR~6.7e-5NIST2 SR~6.7E-6NIST3 SR~6.7e-5
Single Crystal
Damage Layer typically tens of microns
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 15
Elastic Modulus, Single Crystal RRR Nb
Single Crystal Niobium
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014
Strain
Stre
ss (K
SI)
As Received Sliced Ingot
Ingot Sliced with EDM
Heat Treated at 1250C with Ti
Elastic Modulus ~ 120 GPa
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 16
SRF Cavity Performance With Various Nb’s
43 (pulsed)Theoretical limit (185 mT)
4.0 x 109~ 270~ 800 ppm“single crystal”(2.2 GHz)
29.69.45 x 109240~ 1300 ppmFine grain sheet
35.97.5 x 109345~ 600 ppmFine grain sheet
33.57.5 x 109323~ 160 ppmFine grain sheet
31.83.6 x 109~ 700< 500 ppmFine grain sheet
E acc, max [MV/m]
Q0 @ E acc maxRRR - valueTa- contentsMaterial
1500 MHz Cavities at 2 K
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 17
Theoretical Limit Reached
2.2 GHz Single crystal single cell cavityQ0 vs. Bp
1.0E+09
1.0E+10
1.0E+11
0 15 30 45 60 75 90 105 120 135 150 165 180 195
Bp [mT]
Q0
T=2K, after 120C 48h bake T=1.5K after 120C 48h bake T=2K T=1.5K
pulsed
Field emission, after baking
Q-drop
P. Kneisel, G. Ciovati, G. Myneni, J. Sekutowicz, T. Carneiro, Proc. of the 2005Part. Acc. Conf., Knoxville, TN, USA (2005) paper TPPT076
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 18
Thermal Conductivity
10
100
1000
1 2 3 4 5 6 7 8 9 10
Temperature (K)
Ther
mal
Con
duct
ivity
(W/m
K)
Single Crystal Heat TreatedPoly Crystal
Poly Crystal Heat Treated at 1250 C
Two Crystals
Specification should be Thermal Conductivity at 2 K
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 19
Road Map to High Performance, Low Cost SRF Accelerator Structures
• Slice the discs from single crystal ingots
• Remove several tens of microns of damage layer from the completed cavities
• Degass hydrogen at 600 C for several hours and deposit a passivating nitride of several monolayer thickness
• Optimize the operating temperature ~ 1.8 K
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 20
Conclusions
• The presently used high RRR niobium properties appear to be not consistent from batch to batch, from sheet to sheet and even from different locations on the same sheet
• High tantalum content RRR niobium appears to meet all the needs of presently planned projects except ILC at much reduced costs
• Single crystal niobium discs sliced directly from the ingots can be expected to have consistent properties from batch to batch, be less expensive and can be expected to provide high performance and amenable to automated production due to simpler processing steps
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Thomas Jefferson National Accelerator Facility Page 21
Papers related to Single Crystal Niobium on Tuesday Poster Session
• TuP54: Grain Boundary Flux Penetration and Resistivity in Large Grain Niobium Sheet, P. Lee et al
• TuP56: Contamination Analysis of Polycrystalline and Single Crystal Niobium used in Accelerator Cavities by SIMS, F. A. Stevie et al
• TuP57: Comparison of Deformation in High-Purity Single/Large Grain and Polycrystalline Niobium Superconducting Cavities, R.E. Ricker et al
• TuP58: Investigation of Ingot Material with Large Grain for Cavities, X. Singer et al