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Max-Planck-Institutfür Plasmaphysik
Freudenstadt10th October 2007
The roadmap for nuclear fusion
A. M. Bradshaw
Freudenstadt, Oktober 2007 2
G8 Summit Heiligendamm: CHAIR'S SUMMARY
Climate Change, Energy Efficiency and Energy Security:
Combating climate change is one of the major challenges for mankind and it has the potential to seriously damage our natural environment and the global economy.
We noted with concern the recent IPCC report and its findings.
We are convinced that urgent and concerted action is needed and accept our responsibility to show leadership in tackling climate change. Change in mean annual
temperature: Estimated for 2071-2100 relative to 1961-1990, IPCC report, scenario A2. (Here: Fig. 1 in „GREEN PAPER 2007“)
Freudenstadt, Oktober 2007 3
Four important questions
In view of anthropogenic climate change caused by excessive use offossil fuels and dwindling reserves we can ask the following questions:
Will renewable energies be able to replace fossil fuels?
Will politicians be able to persuade an unwilling – or perhaps ill-informed – population to use less energy ?
Can public confidence in nuclear fission be restored?
Can nuclear fusion as a potential sustainable energy source makea significant contribution to the energy supply in this century?
Freudenstadt, Oktober 2007 4
Edward Teller (1959):
“I believe it is extremely important that work on controlled nuclear fusion continue because the end result is valuable and its eventual achievement is probable. Maybe it will be the year 2000, maybe it will be even later.”
Fusion: the so-called moving target
Freudenstadt, Oktober 2007 5
The roadmap for nuclear fusion
Nuclear fusion – an inexhaustible source of energy
Magnetic confinement
No fusion without large experiments
ITER – on the way to a fusion power plant
Freudenstadt, Oktober 2007 6
Fusion of light elements releases energy as does splitting of heavy elements – Fission.
Two ways to utilise nuclear forces
Binding energy per nucleon
2
0
4
6
8
10
1 10 100
n, 1H
2D
3T3He
6Li
9Be4He
10B
12C16O 56Fe
238U
Fusion
Fission
Mass number A
Bin
ding
ene
rgy
[MeV
/A]
Freudenstadt, Oktober 2007 7
Deuterium- Tritium
Fusion – overcoming the Coulomb force
As the number of nucleons increases, the Coulomb repulsion between the nuclei also increases.
Reaction rate depends on tunnelling probability, exp{-Z2/Erel}
Fusion reaction: light nuclei with high relative velocity (high T, plasma)
Freudenstadt, Oktober 2007 8
The sun radiates 1026 Watt and maybe considered as a huge power plant.The energy source is the fusion ofhydrogen nuclei to helium:
Gravity provides the necessary “confinement” in the sun.
1026 Watt
p + p D + e+ +
D + p 3He +
3He + 3He 4He + 2 p ----------------------------------------------------- 4 p 4He + 2 e+ + 2 + 26,7 MeV
Fusion – the energy source of the stars
Freudenstadt, Oktober 2007 9
Reaction probability for DD and DT reactions much higher than for p-p.
A DT plasma is the likely candidate for a fusion power plant
Problems:─ high temperatures (> 100 Mio oC)─ T is radioactive: t1/2 = 12,3 years,→ T not readily available; will have to be bred in situ from lithium
Fusion on earth – the appropriate reaction
Freudenstadt, Oktober 2007 10
D + T 4He + n + 17,6 MeV
Energy is mainly transported by the neutrons. Problem: Activation of materials.
Resources available for millions of years: - D from water: D:H = 1:7000,- T breeding inside
6Li + n 4He + T
Confinement of the hot plasma by magnetic field
Alternative: inertial confinement
Fusion on earth – properties
pn
pn n
pn
np
n
Deuterium
Tritium
Helium(4He)
Neutron
AxKa20060821
Fusion
Freudenstadt, Oktober 2007 11
The roadmap for nuclear fusion
Nuclear fusion – an inexhaustible source of energy
Magnetic confinement
No fusion without large experiments
ITER – on the way to a fusion power plant
Freudenstadt, Oktober 2007 12
Magnetic confinement I: Lorentz force
Lorentz force: charged particles move on spiral orbits along magnetic field lines.
Particle transport perpendicular to the magnetic field B occursonly via collisions.
Unhindered movement parallel to B leads to losses of particlesin a linear field geometry.
Solution: Bend the magnetic field to a torus !
magnetic field
electron ion
Freudenstadt, Oktober 2007 13
Curvature and inhomogeneity of a purely toroidal field result in→ electrons and ions movements in opposite directions, i.e. → charge separation → electric field E.
A resulting E x B drift causes the whole plasma to moveout of the torus.
Solution: Twist the field lines!
Magnetic confinement II: E x B - drift
Freudenstadt, Oktober 2007 14
Magnetic confinement III: Twisting the field lines
There are two competing concepts for twisting the field lines, Stellarators and Tokamaks.
Magnetic field lines
Magnetic flux surfaces
Freudenstadt, Oktober 2007 15
Magnetic confinement IV: Tokamak versus Stellarator
Tokamak Stellarator
WENDELSTEIN 2-A, Deutsches MuseumASDEX Upgrade, Garching
Freudenstadt, Oktober 2007 16
Lyman Spitzer, 1950, Princeton.
Helical external coils provide a poloidal field component which twists the field lines as required.
Advantages+ only external fields+ well controllable+ stationary operation
Disadvantages- nested coils- poor confinement of particles
Optimisation
Modular Stellarators
The Stellarator
Freudenstadt, Oktober 2007 17
WENDELSTEIN 7-X is a modular, quasi-symmetric stellarator completely optimised with numerical methods under construction at the IPP branch institute
at Greifswald – operational in 2014
R = 5.5 ma = 0.53 mBt = 3 T
WENDELSTEIN 7-X – the forthcoming stellarator experiment
In the plasma vessel of W7-X
Freudenstadt, Oktober 2007 18
WENDELSTEIN 7-X: Plasma
Radius: 5.5 mMean minor radius: 0.53 m
Freudenstadt, Oktober 2007 19
WENDELSTEIN 7-X: Plasma vessel
Volume: 110 m3
Surface: 200 m2
Mass: 35 tVacuum: 1…2 · 10–8 hPa
Freudenstadt, Oktober 2007 20
WENDELSTEIN 7-X: Superconducting coils
50 non-planar coils & 20 planar coilsSuperconductor: NbTi (> 3.4 K)Flux density, on axis: 2.5 TFlux density, at coil: 6.8 T @ 17.8 kA
Freudenstadt, Oktober 2007 21
WENDELSTEIN 7-X: Cryostat
Volume: 525 m3
Surface: 480 m2
Vacuum: < 10–5 hPaMass: 150 t
Freudenstadt, Oktober 2007 22
Artsimovitch and Sacharow, Moscow Russian acronym for „Toroidalnayakamera s Magnitnymi Katushkami“(Toroidal chamber with magnetic field)
Plasma is the secondary coil of a transformer, so that a toroidal current is induced.
The plasma current gives rise to a poloidal magnetic field and thus to helical net field which “winds” around the plasma.
The current also heats the plasma.
Problems- pulsed operation (transformer … )- instabilities
The Tokamak
Freudenstadt, Oktober 2007 23
Major radius = 1,65 m, Bt 3,5 T minor radius = 0,5 m, Ip 1,4 MAPH 28 MW, = 1.6
ASDEX Upgrade – a major Tokamak experiment
Start of operation in 1991; here: during construction in 1989
Freudenstadt, Oktober 2007 24
Tokamak – inside ASDEX Upgrade
Freudenstadt, Oktober 2007 25
Plasma-wall interactions
co-deposition viaerosion of C
in W via implantation
ASDEX Upgrade: First tungsten machine
Tritium retention in ITER depending on first wall material (C versus W)
Freudenstadt, Oktober 2007 26
First wall materials – tungsten
• Accidental loss of coolant: peak temperatures of first wall up to 1200 °C
• If contact with air takes place: formation of highly volatile WO3 compounds
• Evaporation rate: order of 10-100 kg/h at >1000°C in a reactor (1000 m2 surface)
→ a large fraction of radioactive WO3 may leave hot vessel
→ Need for development of self-passivating tungsten alloys!
Freudenstadt, Oktober 2007 27
First wall materials – self-passivating tungsten-based alloys
Results of thermo-balance measurements (synthetic air)
Oxidation rate has been calculated from weight in-crease versus time. Compositions are given in wt.%.
• Synthesis of tungsten-based films by sputter deposition
• Thermogravimetric measurements of oxidation behavior at different temperatures in synthetic air
Oxidation rate (mg cm-2 s-1)
6 0 0 ° C
8 0 0 ° C
1 0 0 0 ° C
6 0 0 ° C
8 0 0 ° C
1 0 0 0 ° C
6 0 0 ° C
8 0 0 ° C
1 0 0 0 ° C
1 0- 7
1 0- 6
1 0- 5
1 0- 4
1 0- 3
1 0- 2
1 0- 1
Tungsten:(1.5 µm)
WSi11:(1.5 µm)
WSi10Cr10:(4.5 µm)
Formation of protective oxide layers, reduction of oxidation rate by a factor of 5000 compared to pure tungsten!Cross section of of W-Si-Cr film after
oxidation at 1000 °C for 1h.
Resin
Sapphire substrate 5 µm5 µm
W-Si-Cr alloy
W, Si, WO3, SiO2
Cr2O3
Freimut Koch
Freudenstadt, Oktober 2007 28
The roadmap for nuclear fusion
Nuclear fusion – an inexhaustible source of energy
Magnetic confinement
No fusion without large experiments
ITER – on the way to a fusion power plant
Freudenstadt, Oktober 2007 29
Fusion product
break even
Fusion product nTE n - density T - temperature E - energy confinement time E = Wplasma/Pheating
Power amplification Q = Pfus/Pext
• Q = 1 „break-even“• Q = 20…50 typical for a power plant• Q = ∞ ignition
IgnitionHeating by -particles > Loss (radiation, transport)
nTE > 5*1021 m-3 keV s
Freudenstadt, Oktober 2007 30
Champion: Joint European Torus (JET), Culham/Oxford
To improve the confinementconfinement we need a large experiment!
Source: JET
Freudenstadt, Oktober 2007 31
What we have reached so far
Values reached in different experiments:
• temperature T 400 Mio.°C • density n 1020 m-3 • energy confinement time E ~1,5 s,
which is still too short!
ITER: Due to the larger volume, and thus a longer E, a power amplification factor of Q ≥ 10 is expected!
Why is this the case?
ITER: Pfus = 500 MW, major radius = 6.2 m,minor radius = 2.0 m
Freudenstadt, Oktober 2007 32
Simple (classical) ansatz: Diffusion due to collision
, D 0.0001 m2/s
(: Heat transport coefficient)
transport to the edge
collision
B
Energy confinement and transport I: „classical ansatz“
Provided that the classical ansatz is an appropriate description of the energy transport …
a Tokamak with a ≈ 2 cm should ignite!
The transport of energy determines the energy confinement time E .
E ~ a2/
(: heat transport coefficient,
a: minor radius)
Freudenstadt, Oktober 2007 33
Energy confinement and transport II: „neoclassical ansatz“
The particles in the magnetic field are trapped on „banana orbits“
Diffusion is defined by thewidth of the „banana orbits“
→ , D 0.01 m2/s
→ A Tokamak with a ≈ 20 cm should ignite!
Modified (neoclasscal) ansatz:Inhomogeneities in the magnetic field are observed
Freudenstadt, Oktober 2007 34
Energy confinement and transport III: empirical
Not even the „neoclassical ansatz“ is sufficient to describe energy transport.
Experimental result: Turbulent (anomalous) transport: , D 1 m2/s
ASDEX Upgrade
→ A Tokamak with a ≈ 2 m will ignite!
Variation of ion temperature
Freudenstadt, Oktober 2007 35
Confinement improvement by suppressing turbulance
Internal transport barriers ( continuous operation?)
“Improved” H-mode ( extended operational regime for ITER; discovered at ASDEX Upgrade)
H-mode: Transport barrier at plasma edge
( current ITER standard scenario;
discovered at ASDEX)
Dru
ck
0 r / a 1
Freudenstadt, Oktober 2007 36
Advanced confinment by enlarged experiments
→ similar in shape, growing in size
ASDEX Upgrade JET ITERx 2 → x 2 →
Freudenstadt, Oktober 2007 37
The roadmap for nuclear fusion
Nuclear fusion – an inexhaustible source of energy
Magnetic confinement
No fusion without large experiments
ITER – on the way to a fusion power plant
Freudenstadt, Oktober 2007 38
Source: www. iter.org; www.bundesbank.de
(2005)
(2003)
(… 1999; 2003) (2003)
Joint work sites: Garching, Naka, San Diego
ITER location: Cadarache
28th June 2005: “… ITER shall be sited at Cadarache.”
ITER 2001: 5 bn € Pfus = 500 MW, major radius = 6.2 mminor radius = 2.0 m
Freudenstadt, Oktober 2007 39
ITER – the feasibility of fusion power
Physics goals: Demonstrate an energy producing (“burning”) plasma where the α-particles
emitted by the fusion reaction are the dominat heat source (Q ≥ 10). Reach stationary conditions with non-inductive current drive (Q > 5). Testing “advanced tokamak scenarios” (Q = ∞, ignition not excluded)
Technology goals: availability and integration of essential technologies, e.g. Superconductivity and cryogenics High heat flux and radiation-resistant components Remote handling Fuel technology (tritium cycle) Plasma heating and current drive systems
Freudenstadt, Oktober 2007 40
Roadmap to a fusion power plant
2005 2010 2015 2020 2025 2030 2035 2040 2045 2050
DEMO relevant technologies
ITER
Pla
sma
ph
ysic
s Tokamak physics
First commercialfusion power plant
Stellarator physics (WENDELSTEIN 7-X)
ITER relevant technologiesFirst electrical
power production
DEMO
Fac
iliti
es T
ech
no
log
ies
IFMIF: 14 MeV neutron source
Freudenstadt, Oktober 2007 41
Intrinsic energy/forces (thermal energy, magnetic field, chemical inventory)unperilous for containment
Investment costs for sophisticated technology dominant – negligible fuel costs
Closed tritium cycle
No radioactive primary fuels
The fusion power plant
… and its characteristics
100 years after shutdown materials are completely recyclable → no „permanent disposal waste“
Primary energy carrier (D and Li) available all over the world !!!
Freudenstadt, Oktober 2007 42
Conclusion
“Fusion will be ready when society needs it.”
Lev Andreevich Artsimovich, 1909 – 1973.
How long will it take?
Reserve
Freudenstadt, Oktober 2007 44
Primary energy supply worldwide – and in Germany
<1% others *
24% coal
34% oil
natural Gas 21%
hydro 2%
combustible renewables & waste 11%
nuclear 7%
Sou
rce:
IEA
– K
ey W
orld
Ene
rgy
Sta
tistic
s 20
05
* others: geothermal, solar, wind etc.
Total primary energy supply in 2003:
Germany: 4 000 bn kWhper person and day: 132 kWh
10,6 Gtoe = 443 EJ = 123 000 bn kWh
Freudenstadt, Oktober 2007 45
The end of fossil fuels – oil
Sou
rce:
BG
R, 2
00
3
Freudenstadt, Oktober 2007 46
Renewable energies
Sou
rce:
DLR
technical versus theoretical potential of renewable energies
worldwide primary energy consumption today
wat
er
ge
oth
erm
al
en
erg
y
bio
mas
swin
d
sun
Will renewable energiesbe able to replace
fossil fuels?
Freudenstadt, Oktober 2007 47
ITER – a long “way”
1985, Geneva Summit: Gorbachov suggests to Reagan that the next large fusion experiment be built together with Europe and Japan.
1988: Joint “Conceptual Design” starts at IPP in Garching.
1992: “Engineering Design Activities”, three “Joint work sites”: Garching, Naka (Japan) and San Diego.
1998: ITER proposal (at the right). USA withdrawal.
2001: Re-design of a cheaper and technically less ambitious version results in the current ITER design.
2001-2005: Negotiations on project and site.2003: China and South Korea join, USA rejoin. Site stand-off between Japan and Europe.
ITER proposal 1998: 10 bn € Pfus = 1500 MW, R = 8.1 m
Freudenstadt, Oktober 2007 48
Fusion power: The SUN versus ITER
pp-reaction Type DT-reaction gravitation Confinement magnetic field
1.4 ·109 m Diameter 30 m
150 g/cm3 Density 4 ·10-10 g/cm3
1.5 ·107 °C Temperature 1.5 ·108 °C
1026 Wth Power 5 ·108 Wth
200 Wth/m3 Power density 106 Wth/m
3
Freudenstadt, Oktober 2007 49
Nicht-monotones Stromprofil
Turbulenzunterdrückung
hohe Druckgradienten
großer bootstrap-Strom
• HF-Wellen• NBI
Stationäres Tokamak-Szenario
Freudenstadt, Oktober 2007 50
Radiotoxicity of the waste materials
Sou
rce
: S
afet
y a
nd E
nviro
nmen
tal I
mpa
ct o
f F
usio
n (S
EIF
20
01)
Radioactive waste due to contamination with
tritium (t1/2 = 12,3 years) materials activation by the
intensive flux of high energy neutrons
Main topic for materials research is to minimise materials activation by an appropriate choice of materials compounds.→ recycling is possible after a temporary storage for 100 years.→ no „permanent disposal waste“
Recycling possible
Freudenstadt, Oktober 2007 51
PPCS: Aktivierte Materialien 100 Jahre nach Abschaltung
Kategorisierung der Kraftwerksmaterialien nach Aktivität: NAW Non-Active Waste, SRM Simple Recycle Waste, CRM Complex Recycle Waste, PDW Permanent Disposal Waste.
100 Jahre nach dem Abschalten eines Fusionskraftwerkes bleibt nach der europäischen Kraftwerksstudie PPCS bei keinem der vier untersuchten Kraftwerk-Designs A, B, C und D endzulagerndes Material übrig.
Abfallmengen nach Aktivitätsklassen
NAW SRM CRM PDW
DC
BA
0
20000
40000
60000
80000
100000
Mas
se [
t]
AxK
a20
0609
04
Freudenstadt, Oktober 2007 52
Stromgestehungskosten bei der Kernfusion
Que
lle: w
ww
.efd
a.or
g
PPCS-Studie: Stromgestehungskosten der Kernfusion verglichen mit anderen CO2-armen Energiequellen(angegeben: Kosten für das 10. Kraftwerk seiner Art)
Die europäische Kraftwerksstudie PPCS untersuchte für die vier Kraftwerk-Designs auch die zu erwartenden Stromgestehungs-kosten:
(Hinzu kommen externe Kosten von 0.06 bis 0.09 ct/kWh.)
Schon die erste Kraftwerks-generation (Typ A) ist mit9 ct/kWh wettbewerbsfähig– insbesondere gegenüber der stochastisch anfallenden/nicht planbaren Windenergie.
Spätere anspruchvollere Kraftwerkslinien (Typ D) liegen bei nur noch 3 ct/kWh.
Freudenstadt, Oktober 2007 53
ITER – timeline
Que
lle: w
ww
.iter
.org
S
tand
: Jan
uar
2007
Freudenstadt, Oktober 2007 54
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
En
erg
y t
ec
hn
olo
gy
RD
&D
/ G
DP
[%
]
Government-financed energy R&DD
ata
for
200
5,
Fra
nce a
nd
Fin
lan
d:
200
3,
Qu
elle:
IEA
, En
erg
y s
tati
sti
cs,
R&
D
Sta
tisti
cs,
(on
lin
e)
Access D
ata
base –
200
6 E
dit
ion
Energy sector share of GDP: 10 %
(Germany 2000)
Total spending on R&D is less than 1 % of energy sector turnover.
nature, 30th November 2006:“The ITER fusion project demonstrates a solidity of purpose that is sorely lacking across the rest of the energy research spectrum.“
Freudenstadt, Oktober 2007 55
First wall materials – self-passivating tungsten-based alloys
Results of thermo-balance measurements (synthetic air)
Oxidation rate has been calculated from weight in-crease versus time. Compositions are given in wt.%.
Oxidation rate (mg cm-2 s-1)
6 0 0 ° C
8 0 0 ° C
1 0 0 0 ° C
6 0 0 ° C
8 0 0 ° C
1 0 0 0 ° C
6 0 0 ° C
8 0 0 ° C
1 0 0 0 ° C
1 0- 7
1 0- 6
1 0- 5
1 0- 4
1 0- 3
1 0- 2
1 0- 1
Tungsten:(1.5 µm)
WSi11:(1.5 µm)
WSi10Cr10:(4.5 µm)
Formation of protective oxide layers, reduction of oxidation rate by a factor of 5000 compared to pure tungsten!
• Accidental loss of coolant: peak temperatures of first wall up to 1200 °C
• If contact with air takes place: formation of highly volatile WO3 compounds
• Evaporation rate: order of 10-100 kg/h at >1000°C in a reactor (1000 m2 surface)
→ a large fraction of radioactive WO3
may leave hot vessel
→ Need for development of self-passivating tungsten alloys!
Freimut Koch
Freudenstadt, Oktober 2007 56
Divertor
Additional poloidal fields define thelast closed magnetic surface – separatrix – and create the plasma edge.
As a consequence particles from the plasma edge can be absorbed by a deflector (divertor).
First successful divertor experiments in the 80that ASDEX in Garching:• a cleaner plasma• steepened gradients H-Mode provides a better confinement
Today all large Tokamak experiments have a divertor to dissipate energy and particles.
Stellarators have an intrinsic separatrix.