Max-Planck-Institut für Plasmaphysik Freudenstadt 10 th October 2007 The roadmap for nuclear fusion A. M. Bradshaw

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“)


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?


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



Nuclear fusion – an inexhaustible source of energy

Magnetic confinement

No fusion without large experiments

ITER – on the way to a fusion power plant


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]


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)


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


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


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








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


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


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


Magnetic confinement IV: Tokamak versus Stellarator

Tokamak Stellarator

WENDELSTEIN 2-A, Deutsches MuseumASDEX Upgrade, Garching


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


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


WENDELSTEIN 7-X: Plasma

Radius: 5.5 mMean minor radius: 0.53 m


WENDELSTEIN 7-X: Plasma vessel

Volume: 110 m3

Surface: 200 m2

Mass: 35 tVacuum: 1…2 · 10–8 hPa


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


WENDELSTEIN 7-X: Cryostat

Volume: 525 m3

Surface: 480 m2

Vacuum: < 10–5 hPaMass: 150 t


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


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


Tokamak – inside ASDEX Upgrade


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)


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!


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








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


Champion: Joint European Torus (JET), Culham/Oxford

To improve the confinementconfinement we need a large experiment!

Source: JET


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


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)


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


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


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


Advanced confinment by enlarged experiments

→ similar in shape, growing in size

ASDEX Upgrade JET ITERx 2 → x 2 →








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


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


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


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 !!!


Conclusion

“Fusion will be ready when society needs it.”

Lev Andreevich Artsimovich, 1909 – 1973.

How long will it take?

Reserve


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


The end of fossil fuels – oil

Sou

rce:

BG

R, 2

00

3


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?


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


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


Nicht-monotones Stromprofil

Turbulenzunterdrückung

hohe Druckgradienten

großer bootstrap-Strom

• HF-Wellen• NBI

Stationäres Tokamak-Szenario


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


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


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.


ITER – timeline

Que

lle: w

ww

.iter

.org

S

tand

: Jan

uar

2007

http://www.iter.org/


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.“


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


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.

Documents

Max-Planck-Institut für Plasmaphysik Freudenstadt 10 th October 2007 The roadmap for nuclear fusion A. M. Bradshaw