Nuclear Fusion – Status and Perspectives
Hartmut Zohm
Max-Planck-Institut für Plasmaphysik
85748 Garching
GRS Fachgespräch 2013
Köln, 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
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
Pin = 50 MW
Pout = 2-3 GWth
(initiate and control
burn)
(aiming at 1 GWe)
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
A bit closer look…
Pin = 50 MW
Pout = 2-3 GWth
(initiate and control
burn)
(aiming at 1 GWe)
3.5 MeV
-heating
14.1 MeV
wall loading
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
Plasma can be confined in a magnetic field
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)
Plasma can be confined in a magnetic field
'Tokamak': poloidal field component from current on plasma
Simple concept, but not inherently stationary!
Example: ASDEX Upgrade (IPP Garching)
Plasma can be confined in a magnetic field
'Tokamak': poloidal field component from current on plasma
Simple concept, but not inherently stationary!
Example: ASDEX Upgrade (IPP Garching)
Plasma can be confined in a magnetic field
Outline
What is the basic idea of Nuclear Fusion on Earth?
Where do we stand today?
What are the next steps?
Summary and conclusions
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
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 (ITER)
Fusion specific technology
• plasma heating and diagnostics
• fuel cycle including internal T-breeding from Li (DEMO)
• development of suitable materials in contact with plasma
• development of suited low activation structural material
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 (ITER)
Fusion specific technology
• plasma heating and diagnostics
• fuel cycle including internal T-breeding from Li (DEMO)
• development of suitable materials in contact with plasma
• development of suited low activation structural material
Figure of merit for fusion performance nT
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 ~ Wplasma2
Presently: Ploss compensated
by external heating systems
• Q = Pfus/Pext  Pfus/Ploss ~ nTE
Reactor: Ploss compensated
by -(self)heating
• Q = Pfus/Pext =Pfus/(Ploss-P)   (ignited plasma)
Energy confinement time determined by transport
Simplest ansatz for heat transport:
B
• Diffusion due to binary collisions

• table top device (R  0.6 m)
should ignite!



collision
Transport to the edge
Experimental finding:
• ‚Anomalous‘ transport, much larger
heat losses
• Tokamaks: Ignition expected for R = 7.5 m
R
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
T(0.4)
T(0.8)
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!
ITER (Q=10)
DEMO (ignited)
Major radius R0 [m]
Fusion Power [MW]
Anomalous transport determines machine size
ITER (N=1.8)
DEMO (N=3)
Major radius R0 [m]
• 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
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 (ITER)
Fusion specific technology
• plasma heating and diagnostics
• fuel cycle including internal T-breeding from Li (DEMO)
• development of suitable materials in contact with plasma
• development of suited low activation structural material
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 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
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
Bolometry of total radiated power
Discharge with P/R = 13 MW/m (ASDEX Upgrade)
19
No impurity
seeding
With N2
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
Additional cooling by impurity seeding
19
No impurity
seeding
With N2
seeding
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 (ITER)
Fusion specific technology
• plasma heating and diagnostics
• fuel cycle including internal T-breeding from Li (DEMO)
• development of suitable materials in contact with plasma
• development of suited low activation structural material
Tokamaks have made Tremendous Progress
• figure of merit nTE 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 tokamak
to demonstrate large scale fusion power production: ITER
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 stepladder of tokamak experiments
Diameter
Volume
Fusion power
ASDEX Upgrade
JET
ITER
3.3 m
14 m3
1.5 MW
(D-T equivalent)
6m
80 m3
~ 16 MWth
(D-T)
12 m
800 m3
~ 500 MWth
(D-T)
The ITER Design
ITER
ITER
Major Radius
6.2 m
Minor Radius
2.0 m
Plasma current
15 MA
Magnetic field
5.3 T
(Supercond.)
Power
amplification Q
Fusion power
 10
400 (800)MW
Duration of burn
400 (3000) s
External heating
73 (110) MW
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
Scenario: Standard Low q Hybrid Advanced
Ip [MA]
Bt [T]
N
Pfus [MW]
Q
tpulse [s]
15
5.3
1.8
400
10
400
17
5.3
2.2
700
20
100
13.8
5.3
1.9
400
5.4
1000
9
5.18
3
356
6
3000
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 test
technology elements (e.g. T-breeding) for the next step (DEMO)
The step from ITER to DEMO
ITER = proof of principle for dominantly -heated plasmas
DEMO = proof of principle for reliable large scale electricity production
with 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
DEMO Challenges: Blanket
He subsystems
He-1
Pb-17Li
coolant
manifold
hot shield
cold shield
He-2
2
Pb-17Li
1
ODS Layers
plated to the FW
pol.
rad.
EU Power Plant Conceptual
Design Study (PPCS)
tor.
EUROFER Structure
(FW +Grids)
SiC f/SiC
channel inserts
“Dual Coolant” He-PbLi LM Blanket Design
Tmax ≥ 650°C, 80-150 dpa in DEMO (KIT)
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)
Specific activity (Bq/kg)
DEMO Challenges: structural materials
1 hr
1 day
1 year
100 years
time (log scale)
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)
Plasmaphysics
A Road Map to Fusion Energy
Tokamak physics
Technology
Facilities
Stellarator physics
ITER
DEMO
IFMIF
First
commercial
power plant
First electricity
from fusion
ITER-relevant technology
DEMO-relevant technology
2010
2015
2020
2025
2030
2035
2040
2045
2050
2055
Outline
What is the basic idea of Nuclear Fusion on Earth?
Where do we stand today?
What are the next steps?
Summary and conclusions
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