Ch 4 Superconducting MagnetsCh. 4 Superconducting MagnetsThomas J. DolanASIPP H f iASIPP Hefei2011
SuperconductivitySuperconductorsStabilizationStabilization Coil protectionCoil designLarge coilsLarge coilsMagnetic energy storage
1
2From Dr. Matthias Noe, Karlsruhe Summer School, 2008
From Dr Matthias Noe Karlsruhe Summer School 2008
Dolan SWIP 2009 3
From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Domain of Superconductivity
T K B TT, K B, T
Dolan SWIP 2009 4
Discovery of Superconductors
Kamerlingh Onnes 1911
Dolan SWIP 2009 5From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Discovery of Superconductors
Dolan SWIP 2009 6From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Discovery of Superconductors
Dolan SWIP 2009 7From Dr. Matthias Noe, Karlsruhe Summer School, 2008
TheoryTheoryUsually electron-lattice collisions resistivity
Bardeen-Cooper-Schrieffer:Electron pairs can be coupled by phonons(lattice vibrations) Interact only with each other,
not with lattice no resistivity.
In Cu e-phonon-e interaction is weak, no coupling.
Dolan SWIP 2009 8
At T=0, all electrons are pairedBond energy 2 = 3.5 kTc Tc = “critical temperature”
Dolan SWIP 2009 9
At T>0, some pair bonds are brokenMore unbound electrons Fewer scattering states available
(Pauli Exclusion Principle) weaker electron-phonon interactions weaker electron pair binding weaker electron pair binding
Dolan SWIP 2009 10
At T=Tc , all pair bonds are brokenc p superconductivity lost
Dolan SWIP 2009 11
Energy Gapgy pAt T=0 all electrons are paired
energy gap 2(0) = 3.5 kTc “critical temperature”
Raising T, J, or B heating some pairs split
Each pair split more free electrons fewer possible scattering states for paired e
(Pauli exclusion principle)(Pauli exclusion principle). weaker e-phonon-e coupling, reduced energy gap .
As T increases 0.
Dolan SWIP 2009 12
Coherence Length
1
0
pairedfraction
ns/n
Dolan SWIP 2009 13
0s
Dolan SWIP 2009 14From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Meissner Effect -- Diamagnetism
d2B/dx2 = B/L2
“London penetration depth”L = (omec2/nse2)1/2 = 5.3x106 ns
-1/2
If L = constant, then B = Bo exp(-x/ L)
If ns = 1028 m-3, then L = 5x10-8 m
Bo
B(x)o
Dolan SWIP 2009 15
L
Flux Quantization
Magnetic fluxon o = h/2e = 2.07x10-15 Wb (Weber)
Fluxon is a tube of normalconductivity embedded inthe superconductorthe superconductor.
Tiny ferromagnetic particlesattracted to magnetic fluxonson the surface of superconducting Pb-In alloy.superconducting Pb In alloy.
1 m
Dolan SWIP 2009 16
Type I and Type II Superconductors
Type > 21/2 Lyp LMost pure metals Critical magnetic field Bc = Bco [1 - (T/Tc)2] T = critical temperatureTc critical temperatureType I have Bco < 0.1 T poor for magnets
T II < 21/2 Type II < 21/2 LAllow fluxon penetration into superconductorFluxon penetration begins at “lower critical field” Bc1c1Can carry higher J at higher B than Type I.
Dolan SWIP 2009 17
Flux Penetration into Type II
Flow of vortex currents Around fluxons Around fluxons o.
Each fluxon is in a l i (l )normal region (low ns).
Dolan SWIP 2009 18
Fluxon overlap reduces ns
Spatial variation of superconducting electron density ns
At “upper critical ppfield” Bc2 fluxon overlap large n smallns small superconductivitylost.
Bc2 ~ o/(2)2
Dolan SWIP 2009 19
Fluxons “pinned” in lattice defectsLorentz JxB force pushesfluxons sideways,
t i d b l tti
lattice defects
restrained by latticedefects.
flIf J is high, fluxons canmove from one site to another(“flux creep”) which generates heat
fluxons
( flux creep ), which generates heat.
If many fluxons move, “flux jump” loss of superconductivity
Many lattice defects needed to prevent flux jump.
Dolan SWIP 2009 20
Need for Coil StabilizationFlux jumps local “normal” region J2 heat generation
Inductance prevents current decay (L d/dt voltage)
Heat nearby region normal more heat spreadHeat nearby region normal more heat spread
Need to prevent “quench” (spread of normal region).
Large stored energy could melt coil or rupture cryostat.
Dolan SWIP 2009 21
Cryogenic Coil StabilizationCurrent sharing by copper, rapid heat removal By helium coolant. Stekly number
= resistivityI = currentI currentL = conductor lengthA = conductor area
i bl h t fl 4 kW/ 2q = maximum removable heat flux ~ 4 kW/m2
S = helium coolant contact area
Dolan SWIP 2009 22
Adiabatic Coil StabilizationTiny filaments flux jump heat too small to make T>TTiny filaments flux jump heat too small to make T>Tc
If d ~ 10 m and To ~ 10 K, then Js < 3x1010 A/m2
Filaments must be “transposed”(braided) to prevent current loops between adjacent filamentsloops between adjacent filaments.
Higher J and dJ/dt than cryogenic
Dolan SWIP 2009 23
stabilization.
Tape Wound CoilsThin layer of brittle Nb3Sn on ductile Cu ribbon.
Nb3SnCu
“Dynamic stabilization”
D i f i fl jDamping of magnetic flux jumps + heat removal
Difficult to wind in complex shapes
Canada magnet failureCanada magnet failure.
Dolan SWIP 2009 24
Need for Coil Protection
Quench – 1 GJ coil energy dissipated in small volume gy pmelting, coolant pressure, possible vessel rupture.
Broken circuit arcs puncturing insulation coil caseBroken circuit arcs, puncturing insulation, coil case.
Short circuit to ground – current limiting resistor
Coolant channel blockage quench more probable
Dolan SWIP 2009 25
Protection CircuitProtection Circuit
Quench raises voltage current flows throughQuench raises voltage, current flows through external resistor (bars of iron cooled by water).
R 0 1 Ohm I = 10 kA V = 1000 VRext ~ 0.1 Ohm, I = 10 kA V = 1000 V.
If L = 30 Henry, current decays with time constant
L/R = 300 s.
Dolan SWIP 2009 26
Magnet Safety Analysis
Many potential accidents
Arcs
F lt d t tiFault detection
Local hot spot detectionp
Magnetic energy dump
Organic insulators H2
Dolan SWIP 2009 27
Fault DetectionQuench R , T , He pressure,
Sh t i it R t d b l dShort circuit R to ground , unbalanced currents
Open circuit Voltage B changeOpen circuit Voltage , B change
Coil movement Position sensors
Coolant pump or tube
Flow rate , pressure , quench
Dewar Pressure
Refrigeration T Dolan SWIP 2009 28
Refrigeration T
Low-Temperature Supereconductors
Dolan SWIP 2009 29
From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 30From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Critical Currents of NbTi/Cu Wires
mm
Dolan SWIP 2009 31From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Strain Degradation of Nb3Sn Conductor
Dolan SWIP 2009 32
Comparison of Nb3Sn with NbTi
Dolan SWIP 2009 33From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Hybrid Magnets
Superconducting coil
Normal copper coil
Much higher B thanMuch higher B than Superconducting alone
Much less power thanMuch less power than copper coil alone
Dolan SWIP 2009 34
Summary - Superconductivity
Superconducting domain inside Tc, Bc, Jc surface
Quantized fluxons -- tubular normal regions
JxB force pushes fluxons heat generation
Lattice defects pin fluxons, inhibit motion
Stabilization by current sharing magnetic damping tinyStabilization by current sharing, magnetic damping, tiny
filaments, heat removal
H b id il lt hi h BHybrid coils ultrahigh B
Coil protection to prevent melting
Dolan SWIP 2009 35
Coil DesignCoil Design
Dolan SWIP 2009 36
Coil Design ConsiderationsB field Required N IC d t i I t bili ti i di j i tConductor size, I, stabilization, winding, jointsProtection Fault detection, damage reductionHeat removal Coolant channel, flow rate, pumpingStructural JxB stress, thermal stress, support, pp
windingCryogenics Heat load, refrigerationRadiation damage
Neutron and gamma doses, effects on resistivity and insulators
Dolan SWIP 2009 37
g y
Choice of Conductor
Dolan SWIP 2009 38From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Cable in Conduit
Dolan SWIP 2009 39From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 40From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 41From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Nb3Sn multifilamentary conductorNb3Sn multifilamentary conductor
Dolan SWIP 2009 42From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 43From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 44From Dr. Matthias Noe, Karlsruhe Summer School, 2008
ITER Coils18 Nb3Sn TF coilsBmax = 11.8 TC bl i d it d tCable-in-conduit conductor; wind-react process6540 tons. 150,000 km.,
Nb3Sn Central Solenoid 9 m
Dolan SWIP 2009 45
ITER Coil Systemy
Dolan SWIP 2009 46From Dr. Matthias Noe, Karlsruhe Summer School, 2008
ITER TF Coils
Dolan SWIP 2009 47From Neil Mitchell, SOFT 2008
ITER TF Coils
Dolan SWIP 2009 48From Dr. Matthias Noe, Karlsruhe Summer School, 2008
TF Coil Winding Pack
Dolan SWIP 2009 49From Dr. Matthias Noe, Karlsruhe Summer School, 2008
TF Coil Connections
Dolan SWIP 2009 50From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 51From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 52From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 53From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Insulating the TF CoilInsulating the TF Coil
Dolan SWIP 2009 54From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Installation into TF Coil Case
Dolan SWIP 2009 55From Dr. Matthias Noe, Karlsruhe Summer School, 2008
ITER Toroidal Field RippleITER Toroidal Field RippleITER may need TF ripple < 0.5% to attain Q = 10.ITER may need TF ripple 0.5% to attain Q 10. With 18 TF coils ripple > 0.5%Use Fe inserts between coils.
BB
Dolan SWIP 2009 56
TF Coil Case Manufacture
Dolan SWIP 2009 57
Poloidal Field Coils
Control plasma shape & position
6 NbTi pancake coils
Cable-in-Conduit conductors.
5 will be wound large5 will be wound large coil-winding building
E tra coils madeExtra coils made.
Dolan SWIP 2009 58
PF Coil ClampsPF Coil Clamps
Dolan SWIP 2009 59From Neil Mitchell, SOFT 2008
PF Coil WindingsPF Coil Windings
Dolan SWIP 2009 60From Neil Mitchell, SOFT 2008
PF Coil WindingPF Coil Winding
Dolan SWIP 2009 61From Neil Mitchell, SOFT 2008
Winding ITER PF Coils
Dolan SWIP 2009 62From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Stacking Double Pancakes
Dolan SWIP 2009 63From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Central Solenoid
Dolan SWIP 2009 64
From Neil Mitchell, SOFT 2008
CS Coil Module
Dolan SWIP 2009 65From Neil Mitchell, SOFT 2008
Central Solenoid LeadsTransformer to induce plasma current I ~ 15 MA6Nb3Sn cable-in-conduit coils
Vertical pre-compression structure
Pulsed coils fatigue lifePulsed coils fatigue life4 K Current leads 300 K
Dolan SWIP 2009 66From Neil Mitchell, SOFT 2008
Dolan SWIP 2009 67From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 68From Neil Mitchell, SOFT 2008
Correction CoilsCorrection CoilsEdge Localized Modes (ELMs)“Resonant magnetic perturbations” pedge < ELM levelResonant magnetic perturbations pedge ELM levelFeedback control
Dolan SWIP 2009 69
Dolan SWIP 2009 70From Neil Mitchell, SOFT 2008
TF Coil Procurement
Dolan SWIP 2009 71From Neil Mitchell, SOFT 2008
Dolan SWIP 2009 72From Neil Mitchell, SOFT 2008
2.2 MW 0.63 MW
Dolan SWIP 2009 73From Dr. Matthias Noe, Karlsruhe Summer School, 2008
HTS Current Lead
Dolan SWIP 2009 74From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 75From Neil Mitchell, SOFT 2008
Large Helical Device (LHD)ℓ=2 helical coils
6 circular PF coils
10 field periodsp
National Institute for Fusion Science,Toki Japan
Dolan SWIP 2009 76
Toki, Japan
Coils inside LHD cryostaty
Dolan SWIP 2009 77
LHD CoilsPoloidal Coils inner middle outer Helical Coils
Inner diameter, m 3.2 5.4 10.4 Major radius 3.9 m
Outer diameter, m 4.2 6.2 11.6 Minor radius 0.975 m
W i ht t 16t 25 45 W i ht t 65Weight, ton 16t 25 45 Weight, ton 65
B max T 6.5 5.4 5.0 Bmax, T 6.9
Current, kA 20.8 21.6 31.3 Current, kA 13, ,
# turns 240 208 144 # turns 450
Dolan SWIP 2009 78
LHD Coil Winding Machineg
Dolan SWIP 2009 79
L H li lLarge HelicalDevice,Toki, Japan
Dolan SWIP 2009 80
I t i f LInterior of LargeHelical Device,Toki, Japan
Dolan SWIP 2009 81
Wendelstein 7-X (W7X) Stellarator Coils and PlasmaCoils and Plasma
50 modular coils
Plus 20 circular coils
Each 3.5 m high
5 field periods
Ring support structureg pp
Greifswald, Germany
Dolan SWIP 2009 82
Wendelstein 7-X Cryostat
245 ports for plasma heating & diagnostics. Thermally insulated tubes: vacuum vessel cryostat ports
Dolan SWIP 2009 83
Thermally insulated tubes: vacuum vessel cryostat ports
W 7-X Coil Production
Dolan SWIP 2009 84
W7X Coil after Heating
Dolan SWIP 2009 85
W7X Modular Coil
Dolan SWIP 2009 86
First Assembly Rig6-ton coil vacuum vessel
segment2nd vessel segment brazed on2nd vessel segment brazed on
Thermal insulation installed
More coils & vessel segments Half-module (5 modular Half module (5 modular
+ 2 auxiliary coils)
Bolt on support ringBolt on support ring
Adjust alignments
Dolan SWIP 2009 87
50-ton Half-Module50 ton Half Module
Dolan SWIP 2009 88
Second Assembly HarnessHalf-module is hoisted and joined to other half-module
The support ring segments bolted togetherpp g g g
Plasma vessel halves are brazed. 100-ton module
24 coil leads brazed onto coils, insulated, leak-tested
He coolant tubes are connected, leak-checked
Magnet coil instruments & connecting cables installedg g
Completed module leaves assembly jig after 28 weeks
Dolan SWIP 2009 89
W 7-X Outer Shell
Dolan SWIP 2009 90
Third Assembly – Experiment HallModule hoisted into bottom shell of the outer vessel;
connections and supports are attached. pp
Lifted onto machine foundation, attached to supports.
Top shell of the outer vessel put on and brazedTop shell of the outer vessel put on and brazed.
~60 ports inner vessel outer vessel connected, insulated.
Divertor plates, heat shields, cryopumps installed.
Five modules joined: brazing plasma vessel & outer vessel.
Magnets connected to power supplies, He supplies,
cooling pipes.
Dolan SWIP 2009 91Repeated control measurements and leak tests.
W 7-X InstallationsMicrowave heatingElectric power supplyElectric power supplyCryogenicMachine controlPl di ti tPlasma diagnostic systems
~ 2014 -- uncooled divertor, short pulses, full power.
~ 2017 -- water-cooled divertor 30 minute duration(limited by the external heat-rejection system)(limited by the external heat rejection system).
Dolan SWIP 2009 92
Superconducting Magnetic Energy StorageGoals: to store electrical energy for:Variations between day and nighttime demandSolar and wind power plants.High energy particle acceleratorsPulsed fusion power plantsp p
Potentially better than pumped hydrostorage, compressed air and batteriesair, and batteries.
Dolan SWIP 2009 93
5000 MWh SMES System5000 MWh SMES System
R 0 6 kR = 0.76 kmBmax = 6.8 TH = 15 m108 turnsI 768 kAPressure on rock =Pressure on rock =
3.9x105 N/m2
Dolan SWIP 2009 94
Summary – Superconducting MagnetsSummary Superconducting Magnets
From Dr. Matthias Noe, Karlsruhe Summer School, 2008
Dolan SWIP 2009 95