Transcript Susceptibility Measurements on Niobium for TESLA Cavities Bernd Steffen Universität Würzburg, DESY

Susceptibility Measurements on
Niobium for TESLA Cavities
Bernd Steffen
Universität Würzburg, DESY
TeV Energy Superconducting Linear Accelerator
Outline
• Motivation
• Measuring principles
– Mutual induction ac-Susceptibility measurements
• Sample preparation
• Results
– Unbaked/baked samples
– Variation of baking parameters
– (Baked) Electropolished samples
• Outlook
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
2
Mutual Induction ac-Susceptibility
Measurements
SC-magnet
Primary
ac-coil
Sample
Secondary
(pickup) coils
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• The in-phase U’ and
out-of-phase part U’’ of
the induced signal is
measured with a lock-in
amplifier
• ’ and ’’ are calculated
from these values :
’  U’’/
’’  U’ /
Bernd Steffen
DESY -FDET-
5/24/2016
3
Mutual Induction ac-Susceptibility
Measurements
0,4
• Bc2: Upper
critical field of
the bulk
0,2
0,0
10 Hz @ 4.2 K

-0,2
S
Bc3
• Bc3S=1.7 Bc2S
Surface field
of the surface
layer
-0,4
-0,6
Bc2
-0,8
-1,0
0
100
200
300
400
500
600
700
B / mT
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
4
Mutual Induction ac-Susceptibility
Measurements
• Bc1=
Bc1,meas./(1-N)
• N=0.34
(Demagnetisationfactor)
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
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Sample preparation
• Cylinders, =2.7 mm, h=2.7 mm electroeroded from Nb sheets for cavity production
• ~ 30 m BCP
• 800C annealing in vacuum for 2 hours
• ~ 30 m BCP
• Baked samples:
48 hours at ~120C in vacuum
(< 5*10-7 mbar)
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
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Unbaked / ~120C baked
8000
S
7000
Hc3=
6000
• Unbaked
Bc2 = 267 mT
B02
B03b
Nb,unbaked
Nb,baked
Hc3
• After 120oC
bake
Calculated:
Bc2S = 316 mT
1.7*Hc2
H(Oe)
5000
4000
HC2
3000
2000
HC1
1000
0
0
1
2
3
4
5
6
7
8
9
10
T(K)
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
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Variation of baking parameters
0,4
Baking times
• Baking time:
o
123 C, 10 Hz
0,2
24, 48, 96 hours
0,0
02B, unbaked
09B, baked 24h
07B, baked 48h
27B, baked 48h
08B, baked 96h

-0,2
-0,4
-0,6
• Temperature:
100ºC, 123ºC,
144ºC
-0,8
-1,0
0
200
400
600
B/mT
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
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Variation of baking parameters
0,4
• Saturation after
48 to 96 hours
Baking times
o
144 C, 10 Hz
0,2
0,0

• or even a
reduction of
02B, unbaked
01B, baked 24h
10B, baked 48h
49B, baked 48h
30B, baked 96h
-0,2
-0,4
-0,6
Bc3S ?
-0,8
-1,0
0
200
400
600
B/mT
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
9
Electropolished samples
0,4
Preliminary results of
first measurements!
Electropolished Samples
@ 10Hz, 4.2K
0,2
0,0
Nb02, BCP
Nb14, 40 m EP
Nb12, 150 m EP
Nb53, 210 m EP
-0,2

• No significant
difference after a
light EP (40 µm)
• Large rise of Bc2S
to 306 mT after
150 µm EP
-0,4
-0,6
-0,8
-1,0
0
200
400
600
B/mT
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
10
Baked, electropolished samples
0,4
• Large rise of
Bc2S after
baking
• from 306 mT
to 365 mT
(150 µm EP)
• and
from 282 mT
to 388 mT
(40 µm EP)
Electropolished Samples
@ 10Hz, 4.2K
0,2
0,0
-0,4
Nb14EPB, baked 123C, 48h
Nb12, 150 m EP

-0,2
Nb02, BCP
Nb07B, baked 123C, 48h
Nb14, 40 m EP
Nb12EPB, baked 123C, 48h
-0,6
-0,8
-1,0
0
200
400
600
B/mT
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
11
Oxygen content of the surface layer
• To the oxygen content of Nb+O alloys (with < 1 at% O)
applies the empirical formula (from the data of Koch et al.
1974):
X (in at% O) = (Bc2-276mT)10-3/mT
BCP unbaked
baked 123C, 48h
baked 144C, 48h
150µm EP unbaked
baked 123C, 48h
40µm EP unbaked
baked 123C, 48h
Bc3S/mT Bc2S/mT
464
273
560
329
625
368
520
306
620
365
480
282
660
388
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
at%O
0.00
0.05
0.09
0.03
0.09
0.01
0.11
5/24/2016
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Further Plans
• Depths profiling by anodisation
• Comparable experiments on single and polycrystaline Nb films (E.-A. Knabbe)
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
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Acknowledgments
Thanks to Lutz Lilje und Axel Knabbe (DESY)
and
Sara Casalbuoni and Lars von Sawilski
(Uni Hamburg) for a lot of help
TeV Energy Superconducting Linear Accelerator
Bernd Steffen
DESY -FDET-
5/24/2016
14