Nuclear Fusion – Status and Perspectives...Nuclear Fusion – Status and Perspectives Hartmut Zohm...

Nuclear Fusion – Status and Perspectives

Hartmut ZohmMax-Planck-Institut für Plasmaphysik

85748 Garching

GRS Fachgespräch 2013Köln, 19.02.2013

Outline

What is the basic idea of Nuclear Fusion on Earth?

Where do we stand today?

What are the next steps?

Summary and conclusions

A simplistic view on a Fusion Power Plant

The ‚amplifier‘ is a thermonuclear plasma burning hydrogen to helium

Centre of the sun: T ~ 15 Mio K, n 1032 m-3, p ~ 2.5 x 1011 bar

Pin = 50 MW(initiate and controlburn)

Pout = 2-3 GWth(aiming at 1 GWe)

A bit closer look…

Fusion reactor: magnetically confined plasma, D + T → He + n + 17.6 MeV

Centre of reactor: T = 250 Mio K, n = 1020 m-3, p = 8 bar

3.5 MeV 14.1 MeV-heating wall loading

Pin = 50 MW(initiate and controlburn)

Pout = 2-3 GWth(aiming at 1 GWe)

Toroidal systems avoid end losses along magnetic field

Need to twist field lines helically to compensate particle drifts

Plasma can be confined in a magnetic field

'Stellarator': magnetic field exclusively produced by coils

Example: Wendelstein 7-X (IPP Greifswald)


'Tokamak': poloidal field component from current on plasma

Simple concept, but not inherently stationary!

Example: ASDEX Upgrade (IPP Garching)


Outline





The road to Fusion Energy holds many challenges

Fusion plasma physics

• heat insulation of the confined plasma

• exhaust of heat and particles

• magnetohydrodynamic (MHD) stability of configuration

• self-heating of the plasma by fusion born -particles

Fusion specific technology

• plasma heating and diagnostics

• fuel cycle including internal T-breeding from Li

• development of suitable materials in contact with plasma

• development of suited low activation structural material






• self-heating of the plasma by fusion born -particles (ITER)



• fuel cycle including internal T-breeding from Li (DEMO)



Power Ploss needed to sustain plasma

• determined by thermal insulation: E = Wplasma/Ploss (‘energy confinement time’)

Fusion power increases with Wplasma

• Pfus ~ nDnT<v> ~ ne2T2 ~ Wplasma

2

Presently: Ploss compensatedby external heating systems

• Q = Pfus/Pext Pfus/Ploss ~ nTE

Reactor: Ploss compensated by -(self)heating

• Q = Pfus/Pext =Pfus/(Ploss-P) (ignited plasma)

Figure of merit for fusion performance nT

R

Energy confinement time determined by transport

collision

Transport to the edge

B

Experimental finding:

• ‚Anomalous‘ transport, much largerheat losses

• Tokamaks: Ignition expected for R = 7.5 m

Simplest ansatz for heat transport:

• Diffusion due to binary collisions

• table top device (R 0.6 m) should ignite!

Energy Transport in Fusion Plasmas

Anomalous transport determined by gradient driven turbulence

• linear: main microinstabilities giving rise to turbulence identified

• nonlinear: turbulence generates ‘zonal flow’ acting back on eddy size

• (eddy size)2 / (eddy lifetime) is of the order of experimental values

Energy Transport in Fusion Plasmas

Anomalous transport determined by gradient driven turbulence

• temperature profiles show a certain ‘stiffness’

• ‘critical gradient’ phenomenon – increases with Pheat (!)

increasing machine size will increase central T as well as E

N.B.: steep gradient region in the edge governed by different physics!

T(0.4)T(0.8)

Anomalous transport determines machine size

ITER (Q=10)

DEMO (ignited)

• ignoition (self-heated plasma) predicted at R = 7.5 m

• at this machine size, the fusion power will be of the order of 2 GW

ITER (N=1.8)

DEMO (N=3)

Major radius R0 [m] Major radius R0 [m]

Fusi

on P

ower

[MW

]

Plasma wall interface – from millions of K to 100s of K

• plasma wall interaction in well defined zone further away from core plasma

• allows plasma wall contact without destroying the wall materials

• plasma wall interaction in well defined zone further away from core plasma

• allows plasma wall contact without destroying the wall materials

Plasma wall interface – from millions of K to 100s of K

The perfect wall material: Low-Z or High-Z?

High-Z materials (W, Mo) promise low erosion rates and fuel retention

• if edge temperature is low enough…

ASDEX Upgrade: operation with fully W-coated wall

First successful demonstration of use of W with reactor relevant plasma

• capitalises on low divertor temperatures that lead to negligible erosion

• plasma performance can be equal to that with C-wall

Additional cooling by impurity seeding

Injecting adequate impurities can significantly reduce divertor heat load

• impurity species has to be ‘tailored’ according to edge temperature

• edge radiation beneficial, but core radiation (and dilution) must be avoided

No impurityseeding

With N2seeding

Bolometry of total radiated power Discharge with P/R = 13 MW/m (ASDEX Upgrade)

19

Additional cooling by impurity seeding

No impurityseeding

With N2seeding

19

Tokamaks have made Tremendous Progress

• figure of merit nTE doubles every 1.8 years

•JET tokamak in Culham (UK) has produced 16 MW of fusion power

• present knowledge has allowed to design a next step tokamakto demonstrate large scale fusion power production: ITER

Outline





A stepladder of tokamak experiments

JET6 m

80 m3

~ 16 MWth

(D-T)

ITER12 m

800 m3

~ 500 MWth

(D-T)

Diameter VolumeFusion power

ASDEX Upgrade3.3 m14 m3

1.5 MW(D-T equivalent)

The ITER Design

Major RadiusMinor Radius

Plasma currentMagnetic field

Power amplification Q

Fusion powerDuration of burnExternal heating

ITER6.2 m2.0 m15 MA5.3 T

(Supercond.)

10

400 (800)MW 400 (3000) s 73 (110) MW

ITER

Cost: ~ 15 Billion €Requires world-wide effort

ITER will be built in Cadarache (F) as joint effort – Cn, EU, In, Jp, Ko, RF, US

ITER operational scenarios

ITER operational scenarios aim at fulfilling several physics missions

• demonstrate self heating by -particles (close the loop)

• provide long pulse -heated discharges in reactor-regime to testtechnology elements (e.g. T-breeding) for the next step (DEMO)

Scenario: Standard Low q Hybrid AdvancedIp [MA] 15 17 13.8 9Bt [T] 5.3 5.3 5.3 5.18N 1.8 2.2 1.9 3Pfus [MW] 400 700 400 356Q 10 20 5.4 6tpulse [s] 400 100 1000 3000

ITER = proof of principle for dominantly -heated plasmas

DEMO = proof of principle for reliable large scale electricity productionwith self-sufficient fuel supply

DEMO must be larger: 6.2 m 8.5 m, 400 MW ~ 2 GW

First scoping studies indicate that further advances in physics and technology could be very beneificial

The step from ITER to DEMO

DEMO Challenges: Blanket

Breeding blanket must provide self-sufficient T-supply for fuel cycle

• breeding ratio > 1 needed (1 neutron per fusion reaction n-multiplier)

Blanket also crucial for providing high grade heat (the hotter the better)

He sub-systems

cold shield

SiCf/SiC channel inserts

EUROFER Structure (FW+Grids)

ODS Layers plated to the FW

hot shield

coolant manifold

He-2

He-1 Pb-17Li

Pb-17Li1

2

rad.

tor.

pol.

“Dual Coolant” He-PbLi LM Blanket DesignTmax ≥ 650°C, 80-150 dpa in DEMO (KIT)

EU Power Plant ConceptualDesign Study (PPCS)

DEMO Challenges: structural materials

Progress in materials development needed to fully use fusion advantages

• issue: structural stability at high temperature under 14 MeV neutron-flux

• EUROFER steel up to 550o C (but not below 300 oC), better: ODS

• also reduce waste issues (fuel/burn products itself have short 1/2 12 yrs)

1 hr 1 day 1 year 100 yearstime (log scale)

Spec

ific

activ

ity (B

q/kg

)

2010 2015 2020 2025 2030 2035 2040 2045 2050 2055

DEMO-relevant technology

ITER

Plas

map

hysi

cs

IFMIF

Tokamak physics

Firstcommercialpower plant

Stellarator physics

ITER-relevant technology

First electricityfrom fusion

DEMO

Faci

litie

sTe

chno

logy

A Road Map to Fusion Energy

Outline





Summary and Conclusions

Fusion energy research has made tremendous progress in recent years

• existing database enabled design of next-step device: ITER

Strategy towards fusion energy comprises 3 major facilities:

• ITER to study burning plasma physics and fusion specific technology

• IFMIF to qualify materials (in parallel to ITER)

• DEMO to demonstrate viability of integrated reactor concept

Fusion power plants could be ready to supply energy by 2050

• they will not be too late

• their development will need continuous effort, also in funding

Nuclear Fusion – Status and Perspectives...Nuclear Fusion – Status and Perspectives Hartmut Zohm...

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