Physical and Mechanical Properties of Single
and Large Crystal High-RRR niobium
Ganapati Rao Myneni
SRF 2005 Workshop
Cornell University
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Department of Energy
Collaborators
Peter Kneisel, Gigi Ciovati
Tadeu Carneiro
JLAB
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
Thomas Jefferson National Accelerator Facility
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Page 2
Introduction
• SNS Cavity RRR Niobium Issues
• Hydrogen Workshop November 2002 (ISOHIM)
• Niobium Consortium Formation
• Reference Metals/CBMM CRADA
• Single/Large Grain Niobium Developments
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Types of high RRR bulk niobium
1. Polycrystalline niobium from standard process including rolling &
recrystalization
No apparent control on the microstructure, texture and
Heterogeneity
2. High Tantalum content RRR niobium is available at reduced cost
Measurements 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
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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
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UVa Measurements
400
Grain size (µm)
K
300
200
P
100
N
0
20'
600'
700'
750'
800'
Temperature (C)
Lineal intercept grain size as a function of annealing temperature for the three lots of high-purity niobium
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Interstitials vs RRR (Tokyo Denkai)
Relationship between RRR and interstitial impurities of Niobium
80
NCSU
70
Interstitial impurities concentration [wt ppm
O
N
H
60
C
50
40
30
20
10
0
0
50
100
150
200
250
300
350
RRR
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400
Effect of Tantalum on Mechanical Properties
Optimum Ta 600 – 1000 ppm
800
700
600
load (Pounds)
500
400
300
AS1161A RRR~180
HT1161A
AS1162A RRR~170
HT1162A
AS1163A RRR~150
HT1163A
AS1164A RRR~150
HT1164A
200
100
0
0
10
20
30
40
50
60
70
Percentage of elongation
Thomas Jefferson National Accelerator Facility
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Page 8
Large Grain RRR Niobium
Thomas Jefferson National Accelerator Facility
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Single Crystal Niobium
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RRR Nb from Ingot
Reference Metals RRR Nb from Ingot
600
500
Ta ~ 800 ppm, RRR ~ 280
Load (Pounds)
400
300
RMCIRRR3
RMCIRRR4
RMCIRRR5
RMCIRRR7
RMCIRRR6
RMCIRRR8
RMCIRRR1
RMCIRRR2
200
100
16
14
0
0
10
20
30
40
50
60
70
80
90
100
Percentage of elongation
12
Stress (KSI)
10
8
RMCIRRR3
6
RMCIRRR4
RMCIRRR5
RMCIRRR7
4
RMCIRRR6
RMCIRRR8
RMCIRRR1
2
RMCIRRR2
0
0
0.002
0.004
0.006
0.008
Strain
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Page 11
0.01
0.012
0.014
Polycrystalline RRR niobium
Damage layer ~ 200 to 300 microns
SNS high RRR niobium
18
16
WCASR
WC8006
14
WC80062
Elastic Modulus
~110 GPa
Stress (KSI)
12
WC6006
WC7006
10
WC8001
8
WCASR1
WCL60010
6
WC8003
4
WC7501.5
2
0
0
0.002
0.004
0.006
0.008
0.01
Strain
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0.012
Large Crystal RRR Niobium
After ~ 80 micron BCP 1:1:2
RMS Surface Roughness 27 nm per A. WU/JLAB on a 0.2 X 0.2 mm area
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Single Crystal
Single Crystal RRR niobium
Damage Layer typically tens of microns
600
500
Load (Pounds)
400
300
200
NIST1 SR~6.7e-5
NIST2 SR~6.7E-6
NIST3 SR~6.7e-5
100
0
0
20
40
60
80
100
120
Percentage of Elongation
Thomas Jefferson National Accelerator Facility
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Elastic Modulus, Single Crystal RRR Nb
Single Crystal Niobium
10.0
As Received Sliced
Ingot
9.0
8.0
Stress (KSI)
7.0
Ingot Sliced with
EDM
6.0
5.0
4.0
Heat Treated at
1250C with Ti
3.0
2.0
1.0
0.0
0
0.002
0.004
0.006
0.008
0.01
0.012
Strain
Elastic Modulus ~ 120 GPa
Thomas Jefferson National Accelerator Facility
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0.014
SRF Cavity Performance With Various Nb’s
Material
Ta- contents
RRR - value
Q0 @ E acc max
E acc, max
[MV/m]
Fine grain
sheet
< 500 ppm
~ 700
3.6 x 109
31.8
Fine grain
sheet
~ 160 ppm
323
7.5 x 109
33.5
Fine grain
sheet
~ 600 ppm
345
7.5 x 109
35.9
Fine grain
sheet
~ 1300 ppm
240
9.45 x 109
29.6
“single
crystal”
(2.2 GHz)
~ 800 ppm
~ 270
4.0 x 109
43 (pulsed)
Theoretical
limit (185 mT)
1500 MHz Cavities at 2 K
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Theoretical Limit Reached
2.2 GHz Single crystal single cell cavity
Q0 vs. Bp
T=2K, after 120C 48h bake
T=1.5K after 120C 48h bake
T=2K
T=1.5K
1.0E+11
Q0
Field emission, after baking
1.0E+10
Q-drop
pulsed
1.0E+09
0
15
30
45
60
75
90
105 120 135 150 165 180 195
Bp [mT]
P. Kneisel, G. Ciovati, G. Myneni, J. Sekutowicz, T. Carneiro, Proc. of the 2005Part. Acc. Conf., Knoxville, TN, USA (2005) paper TPPT076
Thomas Jefferson National Accelerator Facility
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Thermal Conductivity
Specification should be Thermal Conductivity at 2 K
Thermal Conductivity (W/mK)
1000
100
Single Crystal Heat Treated
Poly Crystal
Poly Crystal Heat Treated at 1250 C
Two Crystals
10
1
2
3
4
5
6
7
8
9
10
Temperature (K)
Thomas Jefferson National Accelerator Facility
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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
Thomas Jefferson National Accelerator Facility
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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
Thomas Jefferson National Accelerator Facility
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Page 20
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
Thomas Jefferson National Accelerator Facility
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Page 21