Physical and Mechanical Properties of Single and Large ...€¦ · Physical and Mechanical...

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

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



Introduction

• SNS Cavity RRR Niobium Issues

• Hydrogen Workshop November 2002 (ISOHIM)

• Niobium Consortium Formation

• Reference Metals/CBMM CRADA

• Single/Large Grain Niobium Developments



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



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



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



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



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



Large Grain RRR Niobium



Single Crystal Niobium



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



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



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



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



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



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



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



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



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



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



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



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

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