Transcript Document

Capture Solenoid Discussion
A look at Operating Margins in the SC Coils
Peter Loveridge
[email protected]
Rutherford Appleton Laboratory
UKNF Meeting, Lancaster
April-2009
Introduction
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Would like to define a realistic operating surface (J,B,T) for SC capture solenoid coils
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To understand operating margins
To enable study of alternative coil configurations
Strategy:
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2.
3.
Performance of Nb3Sn strands developed for ITER
Define a “Neutrino Factory” cable
Extrapolate cable performance from strand data
Study-2 Capture Solenoid
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Hybrid 20 Tesla Solenoid Magnet
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Combination of high field, large bore, presents a real challenge
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Pion capture is related to B x R
Huge inter-coil forces >10,000 Tonnes
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NC insert generates ~6 Tesla
SC “Outsert” generates ~14 Tesla, Nb3Sn
Lorentz forces are related to B2 x R
Magnet optimisation?
Study-2 capture solenoid
ITER Central Solenoid Model Coil
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In Study-2 (2001), Capture Solenoid performance “Based on” ITER CSMC
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Taken as “State-of-the Art”
Nb3Sn strands
5 stage cable = 3 x 3 x 4 x 5 x 6 = 1080 strands
Conduit dimensions 50 mm x 50 mm
ITER Central Solenoid Model Coil (CSMC) tested 19 Apr 2000
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Achieved 46 kA @ 13 Tesla
ITER Central Solenoid Model Coil (CSMC) Conductor
ITER Central Solenoid Model Coil Assembly in
Test Facility
A Critical Surface Definition for NF Solenoid
STRAND
Critical Surface Data (J vs B) @ 4.2K, ZERO Strain
Assume ITER strand specification (TF cable)
1000
Critical Surface "Strand" Area
900
Critical Surface "Conduit" Area
800
Current Density [A/mm2]
190 A @ 4.2 K and 12 Tesla
0.82 mm diameter strand
Cu:Non-Cu ratio = 1
50% Cable Degradation
700
CABLE
600
Assume a “CSMC like” Cable
500
Strand Diameter = 0.82 mm
Strand Area = 0.528 mm2
400
190 A @ 4.2K, 12 T
300
Total Strands = 1080
No. SC strands = 720 (2/3)
No. Cu strands = 360 (1/3)
200
100
0
0
2
4
6
8
10
12
Field on Conductor [Tesla]
Data scaled from ITER VAC strand measurements
[Courtesy Durham, Supercond. Sci. Technol. 18 (2005) S241-S252]
14
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Conduit Dims: 50 mm x 50 mm
Conduit Area = 2500 mm2
Strain Degrades Nb3Sn Strand Performance!
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Nb3Sn Strand performance is very sensitive to applied strain!
Sources of strain:
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4.
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Cabling
Jacketing
Thermal strain (650˚C to 4.2 K)
Lorentz Forces
ITER experience:
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Operating strain in the strand of the order -0.75 %
Cable degradation is large (50% not unheard of…)
Difficult to predict cable performance from strand data!
Illustration of Strain Degradation in Modern Nb3Sn Strands
(Courtesy ITER Organisation)
Coil Operating Conditions
Coil Operating Parameters @ 4.2K, ZERO Strain
250
100
Critical Surface "Conduit" Area
50% Cable Degradation
60
150
Current [kA]
200
Cable degradation
Current Density [A/mm2]
80
100
40
Study-2 SC Coil
23.4 A/mm2
ITER CSMC
Achieved 46 kA @ 13 T
20
50
0
0
0
2
4
6
8
10
12
14
16
Field On Conductor [Tesla]
Note: 5 % margin on load-line ~ 0.7 Kelvin temp margin
Coil Shielding Issues – Temperature Margin
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Shielding designed to mitigate
beam heating of SC coils
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S pec ific Heat as a F unc tion of T emperature
Steady-state
Instantaneous (pulsed)
1000
Note: a reasonable temperature
margin to aim for ~ 1K
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~ 1 mJ/cc could cause a quench!
S pec ific Heat [J /kg .K ]
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Link with FLUKA power
deposition studies
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Note: Bmax at Rmin
10
1
Material Properties at 4 Kelvin
Material
C opper
Density
Specific Heat @ 4K
mJ/cc.K
[kg/m3]
[J/kg.K]
@ 4K
Copper
8960
0.091
0.82
Niobium
8570
0.400
3.43
Tin
7280
0.245
1.78
Iron
7100
0.382
2.71
Tin
0.1
Niobium
Iron
0.01
1
10
100
T emperature [K ]
Specific heat of coil materials is dramatically reduced at low
temperature
1000
Summary
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Would like to define a realistic operating surface (J,B,T) for the SC capture solenoid coils
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But… strain degradation in cable is large, and not easy to quantify!
Difficult to extrapolate cable performance from strand data
In any case, Study-2 magnet performance already looks optimistic compared to ITER
technology
Questions & Next Steps
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Need to understand what level of strain degradation to expect!
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Look at “whole cable” test data
Interpret SULTAN (PSI) short-sample tests
Is the coil shielding sufficient?
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Small heat capacity in SC coil
Space constraints for shielding in magnet bore