Post on 29-Jan-2016
S.M. Deambrosis*^, G. Keppel*, N. Pretto^, V. Rampazzo*, R.G. Sharma°, D. Tonini * and V. Palmieri*^
Padova University, Material Science Dept
* INFN - Legnaro National Labs ^ Padua University, Science faculty, Material Science Dept
° Interuniversity Accelerator Center, New Delhi
Nb3Sn by Liquid TinDiffusion
Nb3Sn by liquid Sn diffusion
1) Theory
2) Literature review
3) Technique choice reasons
4) Method
5) Work in progress
6) Conclusions
Vapor Sndiffusion
Liquid Sn
diffusion
Usedsystem
“1 Step”
process
“2 Steps”process
“Hybrid”
process
TOeAR
R TKn
n
nBCS
B ,,12
12
3
RBCS
If T < Tc / 2
Empirically, Rres is found to be dependent on n too.
Theory
For low rf losses, a high TC value is not sufficient
A metallic behaviour in the normal state is mandatory
18Tc (K)
ρn
(μΩ
cm)
Nomogram
Theory
RBCS IdealR BCS ~ 1 nΩ
At T = 4.2 K,
f = 500 MHz,
s = 4,
RBCS depends
on Δ and ρn
~ 10 μΩcm
Literature review
Literature
Many papers of different authors with different aims:
• Nb3Sn by CVD and PVD techniques to compare bulk and film properties
• Nb3Sn by bronze process for high field Superconducting Magnets
• Nb3Sn RF application: Wuppertal
Q vs. Epeak of the first two Nb3Sn-coated 1.5 GHz single-cell cavities in comparison to pure Nb at 4.2 K and 2 K f romCEBAF
Wuppertal: Nb3Sn cavity (1.5 GHz) obtained trough Sn vapour phase diffusion (’90s)
Literature
Vapor Sn Diffusion
Technique Choice Reasons
1) Cavity manufactoring
2) Formation of nucleation centers
of Nb3Sn (Nb Surface
Anodization + SnCl2 Treatment)
3) Nb3Sn film growth in a Sn
atmosphere (T = 1050-1250°C,
t = dozens of h, p(Sn) ~ 10-
3mbar)
4) Cool down and unwanted
phases Chemical removal
(anodizaton + HF 48%)
Laboratory Procedure Heating system
Accelerating structure
Sn source
Sn source heater
Pumping system
Liquid solute diffusion technique
Cu
Sn
Nb3Sn
Nb
Technique Choice Reasons
Liquid Sn Diffusion?
Bulk Nb substrate dipping
in a liquid Tin bath
Sample
Annealing
• No nucleation sites on Nb are required
• Fast growth of Nb3Sn layer
• Deasirable uniform thickness
Technique Choice Reasons
Linearfeedtrough
Cooling water jacket
Furnace
Liquid Sn
Furnace
Used System
Method: used system
Nb3Sn: Phase Diagram
Nb3Sn
<Tc
phases
930°C
Method: used system
To Summarise
●Liquid solute diffusion technique choice
●Working T > 930 °C
Linearfeedtrough
Cooling water jacket
Furnace
Liquid Sn
Furnace
1) Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2
solution)
2) Substarte fixing to feedtrough, vacuum and T reaching (1 day)
3) Substrate thermalization (30 min - 1 h)
4) Dipping (few min - 2 h)
5) Annealing above the Sn bath without opening the chamber
(some h)
6) Residual Sn Chemical removal trials
Laboratory Procedure
“1 Step” Process
Method: “1 step” process
Nb3Sn photo
Residual Sn
Sn drop
Method: “1 step” process
SEM Image
10 m
Nb
Nb3Sn
Method: “1 step” process
Process T = 1000°C
Dipping t = 120’
Annealing t = 14h
Post annealing:
5h at 500°C
XRD spectrum
Method: “1 step” process
Dipping T = 1000 °CDipping t = 30 min
Annealing T = 1000 °CAnnealing t = 10 h
Dipping T = 1000 °CDipping t = 30 min
Annealing T = 1000 °CAnnealing t = 10 h
Angle 2θ (degrees)
Rel
ativ
e In
tens
ity
Process T = 1000°C, Dipping t = 30’, Annealing t
= 10h
EMPA Analysis
Distance (m)
Sn
at.%
Distance (m)
Sn
at.%
Nb3Sn n°16
Dipping T = 1000 °C
Dipping t = 120 min
Annealing T = 1000 °C
Annealing t = 14 h
Post annealing T = 500
°C
Post annelaing t = 5 h
Method: “1 step” process
A Superconductive Transition Curve
Temperature (K)
M’ (
emu)
Nb3Sn 16: 970°C; 120’+14h. Post annealing: 500°Cx5hNb3Sn 16: 970°C; 120’+14h. Post annealing: 500°Cx5h
Nb3Sn (Tc = 17,7 K)
Nb (Tc = 9,3 K)
Sn (Tc = 3,6 K)
Nb3Sn n°16: 1000°C; 120’+14h+post annealing 500°Cx5h
Method: “1 step” process
• Mechanical polishing
• Chemical polishing
3. Q Factor Measurement
• Nb3Sn film obtainment
6 GHz Cavities
1. Spinning Technique
2. Surface Treatments
Method: “1 step” process
T = 1025°C
tdipping = 15 min, tannealing = 15 h
HCl 37%,
t = 10 min, T = 85°C
Nb3Sn film obtainment
Film production:
Chemical treatment:
Method: “1 step” process
Q Factor Measurement
Nb3Sn
Method: “1 step” process
A Nb3Sn 6 GHz Cavity
Nb3Sn 1
1) As obtained
2) HCl
3) HCl + us
Method: “1 step” process
Nb3Sn with good superconductive properties
Residual Sn traces on the sample surface
To Summarise
+Tc = 16,9 K Tc= 0,2 K
-
Sn rich Phases Presence-
Method: “1 step” process
“2 Steps” Process
Method: “2 steps” process
1) Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2
solution)
2) Substarte fixing to the feedtrough, vacuum and T reaching (1
day)
3) Substrate thermalization (30 min - 1 h)
4) Dipping (few min - 2 h)
5) System opening to remove Sn bath, vacuum and T reaching (1
day)
6) Sample annealing without Sn vapor (some h)
7) Growth film chemical treatment
Linearfeedtrough
Cooling water jacket
Furnace
Liquid Sn
Furnace
Laboratory Procedure
Nb3Sn photo
Method: “2 steps” process
SEM Images
Method: “2 steps” process
Proc T = 1025°C, Dipp t = 15’, Ann t = 15h
Proc T = 1025°C, Dipp t = 5’, Ann t =
20h
XRD spectra
Angle 2θ (degrees)
Rel
ativ
e In
tens
ity
Angle 2θ (degrees)
Rel
ativ
e In
tens
ity
Method: “2 steps” process
Proc T = 1025°C,
Dipp t = 5’,
Ann t = 20h
Proc T =
1025°C, Dipp t
= 5’,
Ann t = 10h
A Superconductive Transition Curve
Method: “2 steps” process
-0,028
-0,026
-0,024
-0,022
-0,02
-0,018
-0,016
-0,014
-0,012
1 3 5 7 9 11 13 15 17 19
Temperature (K)
M' (
em
u)
Proc T = 1025°C, Dipp t = 5’, Ann t =
20h
Tc (Nb3Sn) = 14,9 K
Tc (Nb3Sn) = 0,43 K
Growth film chemical treatment (HCl)
Method: “2 steps” process
Tc and Tc vs THCl
T HCl (°C)
T HCl (°C)
Method: “2 steps” process
Worst Nb3Sn film superconductive properties
+
-
To Summarise
No Residual Sn traces on the sample surface
Tc = 15,2 K, Tc = 0,5 K
Sn rich Phases Presence-
Method: “2 steps” process
HCl chemical treatment deteriorates the growth film-
“Hybrid” Process
Method: “Hybrid” process
Laboratory Procedure
1) Bulk Nb Substrate chemical cleaning (10 min in a 1:1:2
solution)
2) Substarte fixing to the feedtrough, vacuum and T reaching (1
day)
3) Substrate thermalization (30 min - 1 h)
4) Dipping (few min - 2 h)
5) Sample annealing with Sn vapor (some h)
6) System opening to remove Sn bath, vacuum and T reaching (1
day)
7) Sample annealing without Sn vapor (some h)
Linearfeedtrough
Cooling water jacket
Furnace
Liquid Sn
Furnace
Method: “Hybrid” process
Nb3Sn photo
XRD spectrum
Angle 2θ (degrees)
Rel
ativ
e In
tens
ity
Method: “Hybrid” process
Proc T = 975°C, Dipp t = 30’, Ann (Sn) t = 2h, Ann t
= 5h
A Superconductive Transition Curve
Method: “Hybrid” process
Proc T = 975°C, Dipp t = 30’, Ann (Sn) t = 2h, Ann t
= 5h
-0,028
-0,026
-0,024
-0,022
-0,02
-0,018
-0,016
-0,014
-0,012
1 3 5 7 9 11 13 15 17 19
Temperature (K)
M' (
emu)
Tc (Nb3Sn) = 16,6 K
Tc (Nb3Sn) = 0,28 K
Good Nb3Sn film superconductive properties
+No Residual Sn traces on the sample surface
Tc = 16,5 K, Tc = 0,3 K
No Sn rich Phases
To Summarise
+
+
Method: “Hybrid” process
Work in progress
• Two furnaces system to avoid air contamination of the
superconducting thin film while opening the vacuum
system
• Use of the best results to coat 6 GHz Nb cavities for a
Nb3Sn RF properties sistematic testing
• Use of a different experimental method to prepare
Nb3Sn:
multilayer obtained altermatively depositing Nb and Sn
Conclusions
• Liquid solute diffusion technique (working T > 930 °C)
• Three different processes:
“1 step”
“2 steps”
“Hybrid”
trying to optimize T and t
• Finally:
◊ Good superconducting properties
◊ No Sn
◊ No Sn rich Phases
End