FusionWill it always be…

The power source of the future

Plasma in spherical tokamak START

TOKAMAKTen times

the temperature

of the sun

ITER – the WayCaderache, France, Open 2016

500Mw 400 seconds

ITER - costsCurrent estimate total €5 billion (JET on budget)

Double LHC, Half SSC (at cancellation) 10% Space Station

Indicative Single-year EU subsidies to existing generation methods 2001 (European Environmental Agency, 2004)

Coal €13 billion Oil/gas €8.7 billionNuclear €2.2 billion Renewables €5.3 billion

Making electricityEnergy is primarily contained in

neutrons, alpha particles.

Capture these in a “blanket”, heat up water, sodium, Pb etc.

Heat exchanger to run a steam engine.

None of this will be done at ITER. Next Machine, DEMO, will make power

DEMO – Non-commercial power generation

Materials

Plasma facing materialFirst wallBlanket MaterialReaction pressure vesselElectronics… Magnets…

Challenges for fusion materials technology

•Low Activation – decommissionability

•Very high heat loads for materials

facing the plasma

•Damage to the structure caused by

high-energy neutrons

•Production of tritium in situ

•Helium embrittlement

•Sputtering on surface & poisoning of plasma by heavy ions

Radiation Damage

SimulationsPrevious Edinburgh Funding:

Four EU FP6/7 PDRA grants with various industrial partners (EDF, SCK, FZK)

ITEM, PERFORM, PERFECT, GETMAT

One EPSRC PDRA joint with Culham & Oxford

Total value to Edinburgh ~£500,000

SUPA funding: none.

Radiation damages the materials from which a reactor is made. This determines reactor lifetimes.

A non-equilibrium process, it has unknown scaling with time and dose. Modelling required.

Edinburgh: Graeme Ackland and Derek Hepburn

First principles studies of “primary damage” (point defects).

Simplified atomistic force models for metals.

Molecular dynamics of evolution of damage, and emergent objects (dislocation loops, hardening, voids, etc.)

Dynamical system

Radiation inDefects producedDefects recombine or

migrate to sinks

Sinks grow (voids lead to swelling) and may saturate (grain boundary segregation)

Not at Thermodynamic Equilibrium

Voids in Si after 10keV irradiation

•Vanadium swells (vacancies form voids)

•V + Fe brittle, doesn’t swell

•V + Fe + Cr neither - but why?

International Fusion Materials Irradiation Facility (IFMIF)

Environments – First Wall

Bombarded by 14MeV neutrons (alphas are contained by magnetic field).

At 500oC for commercial reactor.200 dpa (five year lifetime)

Immune to radiation damage in presence of He.Immune to transmutation to long lived

isotopes.Weldable, formable, corrosion resistant etc.

etc.Must not poison plasma, sputter

Candidates – First Wall

Vanadium (+Cr,Ti).Ferritic/Martensitic Stainless Steel (FeCr)Oxide Dispersion Strengthening (ODS)SiCDiamond coating

Environment - Blanket

Immediately behind the first wall

Protect the magnets from radiation (ITER)

Convert neutron energy to heat (DEMO)

Produce tritium for reaction (DEMO)

Liquid – avoid damage – water, LiPb

Environment – Pressure Vessel

Contain coolantResist neutron bombardmentHigh temperature

Stainless steel

Multiscale modelling of fusion materials

•Engineering properties depend on

•microstructures that depend on

•properties of defects that depend on

•interatomic interactions that depend on

•electronic structure of the material

How materials deform

Creep – 0D (point defects)My Video\nhcreep[1].mov

Dislocations – 1D (line defects)My Video\dislox[1].mov

Edinburgh Speciality: Interatomic potentials

Computational elegance -Want force on atoms as a function of atomic degrees of freedom only. Simulate billions of atoms (microns)

Use insight from quantum mechanics – beyond pair potentials

Energy as a functional of pairwise interactions

Fit parameters of the functional to relevant properties of the material (phase diagram, defect formation etc)

Atomistic simulations

Interstitial defects in body-centred cubic Fe

<110> diffuses slowly, <111> quickly

Not an atom moving - Impurities pin defects.

Radiation DamageWhen radiation hits metal – one atom

acquires enormous energy.

3D billiards with a million balls

Empty site – vacancy (red) Doubly-occupied site – interstitial

(green)

ClusteringCu 25keV cascade 100K 74FP.mov

Vacancies - the theory of nothing

Vacancies cluster near initial event 3D void

But … a 3D void comprising vacancies can collapse to form a 2D platelet

Or, if top and bottom of platelet match, the only defect is a 1D loop around the edge.

Vacancies are not conservedHow to describe material transport?

Emergent interstitial features

Interstitials form 2D platelets (anisotropic strain).But these are really 1D dislocation loopsSimulation shows they move really fastCan sweep up defects as they go through the

material (nanoscale cleaners?)

Which are the important defects?

We don’t know. Maybe all lengthscales are important?

e.g. Ionic crystalCharged defects move and attract makingDipole defects move and attract makingStatic quadrupole defects, but captureDipoles making 6-mers move and attract..

Nothing can stop dislocations! (vacancy

pinning)339V_sr5_100K.mov

Unknown unknownsCopper particles in Steel

•bcc, commensurate 9R then fcc

•Embrittling effect small, large, smaller

Voids observed near a grain boundary

Drag impurities in, or out

Formation and growth of voids

HeliumUnavoidable in Fusion: D+T = He + nHelium hates being in metals – goes to voids,

causes swelling attracts other He, emits interstitials.

He voids nucleate on grain boundaries and cause embrittlement

Introduce other sinks (precipitates) to capture He, or “nanopipes” to extract it to the surface – need to understand what attracts it.

Formation and growth of voids

Experiment versus KMC theory.

Summary – not much known

Radiation damage is a unique environment

Driven, complex system – thermodynamics need not apply – extrapolation dangerous

Experimental study of 14MeV neutrons expensive (IFMIF) but necessary

Where can simulation focus, enhance, or replace experimentation?

Who would believe it?

The energy source of the future?

Maybe…

The fusion reactions

REACTION 1: D + D = He3 + n

REACTION 2: D + T = He4 + n

Very high energy and pressure

Various test projects

We know how to do it.

Nuclear issues resolved

Plasma control is not (Torus/sphere)

Materials issues are not

Confined Nuclear Fusion

ITER