Superconductor based fusion energyAsger Bech Abrahamsen, Ph.d., Senior Scientist
Materials Research Division, Risø-DTU, RoskildeFusionsklassen, ScienceTalenterMærsk Mc-Kinney Møller VidencenterSorø, November 15 (2010)
Risø DTU, Technical University of DenmarkRisø DTU, Technical University of Denmark
Outline• Can fusion prevent global warming?
• The Energy challenge
• Fusion and magnetic confinement
• Geometries and realizations
• ITER and superconductivity
• Superconductors for the fusion reactor beyond ITER
• Superconducting wind turbines?
• Conclusion
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Motivation : Sex
[ ]( )tNtN βα −= exp)( 0
Birth rate : α(N, food, pollution, techno, energy,. )
NNdtdN βα −=
Birth rate : α Death rate : β15-11-2010Fusions Klassen, Science Talenter
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The energy Challenge
• Coal, oil and natural gas → CO2 emission → Global warming• UN recommendation : 60-80 % fossil fuel reduction by 2050 • Fusion is a long term alternative for stable & clean energy.
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Fusion time line
15-11-2010D. Clery, Science 314, 238 (2006)
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Fusion
Star based• H + H → He + energy• Confinement by gravity
Earth based• D + T → 4He + n + 17.6 MeV• 6Li + n → T + 4He + 4.78 MeV• 7Li + n(E>2.5 MeV) → T + 4He + n
Fuels• Water contains 30 g/m3 of D• Li can be found in earth crust
Conditions• T > 100 million oC
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SOHO,NASA
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Magnetic confinement of a plasma
• Plasma = gas of nucleus D+, T+ & 4He2+ and electrons e-
• Charge neutral• Plasma pressure:
• Magnetic energy density:
• Plasma and magnetic pressure ratio:
• Energy production:
Tnkp B=n: particle density
kB: Boltzman
T: Temperature
[ ] PamN
mNm
mJB
====⇒= 2330
20
2ε
µε B0: Magnetic field
μ0: Vac. permeability
εβ eion pp +
=
+
= 32
40
2
13.4
mMW
TeTiBPDT
β
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Particle movement
• Equation of motion of a charged particle:
• m: Mass• v(t): Velocity• q: Charge• E(r,t): Electric field• B(r,t): Magnetic Field
• Circle movement in homogenous field • Gyro radius
[ ]),()(),()( trBtvtrEqdt
tvdm ×+=
qBmvR ⊥=
e-D+
VeVD
fefD
BR
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Coil
Field lines
Torus geometryHomogenous magnetic field inside torus
Non-homogenous magnetic field• Magnetic gradient drift: Vd,grad ~ Φ x R Φ: magnetic flux• Centrifugal drift: Vd,cen ~ R x Φ R: Radial vector
• Positive charges drift down and negative up → Instability
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TokamakSolving ideal magnetohydrodynamic equations suggest helical B field
• Induce plasma current by central coil to generate poloidal field component → Pulsed operation.
D. Clery, Science 314, 238 (2006)
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Stellarator• Helical magnetic field inside torus created by DC coils
• Upcoming technology decades behind tokamak machines• NbTi superconductor: B = 6.7 tesla @wire & T = 4.2 K
WENDELSTEIN 7-X, Garching(D)
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Superconductors and high magnetic field
• Electrons pair due to lattice distortion• Quantum fluid of Cooper pairs (+k↑, -k↓)• R = 0 !
• Magnetic field causes rotational flow• B = 0 Meissner state H < Hc1
• Vortex state Hc1 < H < Hc2
• Quantization of flux Φ0 = h/2e
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Vortex movement and pinning
• Lorentz like force is acting on vortex lines when a supercurrent is flowing• Energy dissipation → Flux flow resistance• Pining by defects & impurities• Same size as vortex core • R = 0 only when J < JC
H
H = 0.002 Tesla
J
zJf 0Φ×=
f
∫= fdxw
Pinning centers
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Critical surface of practical superconductors
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• Temperature • Magnetic field (angular)• Stress• Thermal cycling• Magnetic field cycling
• Neutron dose
Engineering current density
Je,Cu ~ 2-7 A/mm2
= 2mm
AA
IJconductor
Ce
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Creating magnetic fields: Soleniod
15-11-2010
tJHBtJHtlJHl
dSJHdl
dSJdSH
JH
e
e
e
00 µµ ===
⇒=
⇒=
⇒=×∇
⇒=×∇
∫ ∫∫∫
l
t
a0
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Superconducting materials
• Most simple metals• Metallic alloys• Semiconducting ceramics !
Gurevich at. al., SuST17,278 (2004)
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International Thermonuclear Experimental Reactor(ITER)
• Plasma• Rmajor: 6.2 m• Rminor: 2.0 m• Volume: 840 m3
• Current: 15.0 MA• Temperature: 108 oC
• Toroidal B: 5.3 tesla• Power: 500 MW• Burn: > 400 sec• Amplification: > 10
• Price: 5 Billion €• 25 % to superconductors• Site: Cadarache (F)
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Toroidal field coils• 18 coils : 9 x 14 meter
• Nb3Sn superconductor (760 km x 18)
• B = 11.8 Tesla @ conductor
• Forced flow liquid Helium
• I = 68 kA
• Transverse force : 800 kN / m80 tons / m
• Stored energy : 2300 MJ / coil
• Je = 67 A/mm2
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Wire → cable → coil
• Wire: Nb + Sn in metal matrix → Nb3Sn• Nb3Sn is brittle !• Wind coil & react at T = 650 oC & 240 hours• Cable: Center flow tube for Liquid He
Wires wrapped in CuStainless steel conduit
• Insulation applied after heat treatment
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Central field coil
• Nb3Sn superconductor (1489 km x 6)• Stabalizer : Cu• Conduit: Nickel superalloy
• B = 13.5 tesla @ conductor• I = 46 kA, Je = 45 A/mm2
• Ramp rate : 1 tesla / sec
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Outer poloidal and correction coils
• 6 coils : R = 4.5 m, 8.5 m & 12.0 m• NbTi superconductor• Stabalizer : Cu• Conduit: Stainless steel
• B = 5 & 6 tesla @ conductor
• 18 correction coils:• NbTi superconductor• B < 5 tesla @ conductor
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The fusion reactor in 2050Beyond ITER (Power Plant Conceptual Study PPCS report, EFDA 2005 )
Model A B C DP(GW) 5.0 3.60 3.41 2.53
TFaxis(T) 7.0 6.9 6.0 5.6
TFcond(T) 13.1 13.2 13.6 13.4
Efficiency 31 % 36 % 44 % 60 %
ITER : TF on axis = 5.3 Tesla
TF on Nb3Sn = 11.8 Tesla
PPCS : 20 % improvement &
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Choice of superconductor?
• Can we get the high temperature superconductors ready? SuST19,S27(06)
40 60 80 100 120200
0
60
80
100
T [K]
Hc2 [T]
YBa2Cu3O6+x Bi2Sr2Ca2Cu3O10+x
20
40
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Choice of superconductor?
American Superconductor(AMSC) 2G HTc
Grivel, Risø
SuST19,S27(06)
SuST19,S4(06)
Sumitomo
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Superconducting wind turbines?
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500 km
120 GW10 MW
12000 units120 x 100 km
v0
A = πR2
20 0
0
12
RP v Av Cpvωρ
=
Risø DTU, Technical University of DenmarkRisø DTU, Technical University of Denmark
Generator principle
2Power BI D l ω∝
1G : Copper + Iron2G : Permanent magnets + Iron3G : HTc Superconductors
I
B
l
r
• Lorentz force on wiref = I × B l
• Torque on wiresτ = 2 r × f
= BI Dl
• PowerP = τ ω
f
Direct drive: 1500 rpm → 15 rpm !Increase size or increase BI
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5 MW Multi-pole synchronous generator
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Warm rotor and stator Fetcryostat ~ 4 cm
Bairgap ~ 2.3 TeslaBFe < 2.5 TeslaAstator ~ 90 kA/mCu loss ~ 5 %
• 24 poles • R = 4.2 m• Lactive = 1.2 m• mactive = 34 tons
• Compete with Nd2Fe14B PM• Using only kg of Rare Earths elements instead of tons
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Conclusion• Fusion is a long term strategic technology
• Energy security and backup for renewable sources
• Superconductor are likely to play a central role using magnetic confinement.
• Low temperature superconductor will do the job… But
• Depend on Liquid Helium• Operate at low temperature -> Expensive• Will become activated by the neutron radiation
• Are the High temperature superconductor ready? In principle but more research and development are needed.
• Superconducting wind turbines as a first step?
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ContactAsger Bech Abrahamsen
Superconductivity and magnetism groupMaterials Research DivisionRisø National Laboratory for sustainable energyTechnical University of DenmarkBuilding 229, Room S47Frederiksborgvej 399DK-4000 RoskildeDenmark
Tel.: +45 4677 4741Fax.: +45 4677 5758Mobile: +45 2617 8757E-mail: [email protected]
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