1. Fusion: Basic Principles, Current Progress and ITER Plans
Mohamed Abdou
Distinguished Professor, Mechanical and Aerospace Engineering Department
Director, Center for Energy Science and Technology Advanced Research (CESTAR)
Director, Fusion Science and Technology Center
University of California Los Angeles (UCLA)
Plenary Talk presented at the 9th International Cairo Conference on Energy and Environment

2. What is Nuclear Fusion?
Nuclear Fusion is the energy-producing process taking place in the core of the Sun and stars
The core temperature of the Sun is about 15 million °C. At these temperatures hydrogen nuclei fuse to give Helium and Energy. The energy sustains life on Earth via sunlight

3. Energy Released by Nuclear Reactions
Light nuclei (hydrogen, helium) release energy when they fuse (Nuclear Fusion)
The product nuclei weigh less than the parent nuclei
Heavy nuclei (Uranium) release energy when they split (Nuclear Fission)
The product nuclei weigh less than the original nucleus

4. Energy Released by Nuclear Fusion and Fission
Fusion reactions release much higher energies than Fission reactions

5. Fusion Reactions
Deuterium – from water (0.02% of all hydrogen is heavy hydrogen or deuterium)
Tritium – from lithium (a light metal common in the Earth’s crust)
Deuterium + Lithium → Helium + Energy
This fusion cycle (which has the fastest reaction rate) is of interest for Energy Production

6. The World, particularly developing countries, needs a New Energy Source
Growth in world population and growth in energy demand from increased industrialisation/affluence will lead to an Energy Gap which will be increasingly difficult to fill with fossil fuels
Without improvements in efficiency we will need 80% more energy by 2020
Even with efficiency improvements at the limit of technology we would still need 40% more energy

7. Incentives for Developing Fusion
Fusion powers the Sun and the stars
It is now within reach for use on Earth
In the fusion process lighter elements are “fused” together, making heavier elements and producing prodigious amounts of energy
Fusion offers very attractive features:
Sustainable energy source
(for DT cycle; provided that Breeding Blankets are successfully developed)
No emission of Greenhouse or other polluting gases
No risk of a severe accident
No long-lived radioactive waste
Fusion energy can be used to produce electricity and hydrogen, and for desalination

9. Fission (PWR)
Fusion structure
Coal
Tritium in fusion

10. Fusion Energy – Disadvantages
Fusion reaction is difficult to start!
High temperatures (Millions of degrees) in a pure High Vacuum environment are required
Technically complex and high capital cost reactors are necessary
More Research and Development is needed to bring concept to fruition
The physics is well advanced but requires sustained development on a long time scale (20 to 40 years)

11. The President recognizes Fusion’s potential

12. Fusion Power Station Schematic

13. Plasmas
A Plasma is an ionised gas. A mixture of positive ions and negative electrons with overall charge neutrality
Plasmas constitute the 4th state of matter, obtained at temperatures in excess of 100,000 degrees
Plasmas conduct electricity and heat

14. Self-Sustaining or ‘Ignited’ Plasmas
Deuterium – tritium fusion reaction:
D + T → 4He + n + Energy
The 4He nuclei (‘a’ particles) carry about 20% of the energy and stay in the plasma. The other 80% is carried away by the neutrons and can be used to generate steam.
Plasmas become Self-sustaining or Ignited when there is enough a power to balance losses from the plasma
In stars plasma particles (including a’s) are confined mainly by gravity and high plasma densities achieved
On Earth:
hot dense plasmas can be confined in Magnetic fields (Magnetic Confinement Fusion)
superdense plasmas can be obtained by imploding solid deuterium-tritium pellets (Inertial Confinement Fusion)

15. Inertial Confinement
Laser implosion of small (3mm diameter) solid deuterium–tritium pellets produces fusion conditions
Pressure generation
Compression
Fuel is compressed by rocket-like blow off
200,000 million atmospheres in core
Ignition and burn
Peak compression fuel reaches times liquid density for extremely short time (10–11 seconds)
Core is heated and ‘spark ignition’ occurs

16. Magnetic Confinement
Magnetic fields cause charged particles to spiral around field lines. Plasma particles are lost to the vessel walls only by relatively slow diffusion across the field lines
Toroidal (ring shaped) system avoids plasma hitting the end of the container
The most successful Magnetic Confinement device is the TOKAMAK (Russian for ‘Toroidal Magnetic Chamber’)

17. The Tokamak: A Transformer Device

18. confinement time > 5 seconds
How Large a Device?
For fusion power to ignite a plasma:
There has to be sufficient density of deuterium and tritium ions (ni);
The reacting ions have to be hot enough (Ti);
The energy from the fusion a’s must be confined for long enough (tE).
tE increases with the square of the device size – a large machine is needed.
The fusion triple product (niTitE) and the ion temperature (Ti) must both be large enough (below a certain temperature the fusion reaction probability is too small)
pressure (niTi) ≥ 2 atmospheres
confinement time > 5 seconds
plasma ion temperature ≈ Million °C

19. JET (Joint European Torus)
The Joint European Torus (“JET”) is the largest magnetic fusion test device in the world.
Situated at Culham, Oxfordshire, JET:
was constructed between ;
has operated present;
is the largest Project in the European Union’s Fusion programme
The participating countries are the 15 EU nations + Switzerland
The Project has a capital investment of over £500 Million and an Annual Budget of around £53 Million

20. JET JET is a Tokamak with: Torus radius 3.1m
Vacuum vessel 3.96m high x 2.4m wide
Plasma volume 80m3
Plasma current up to 5MA
Main confining field up to 4 Tesla (recently upgraded from 3.4 Tesla)

21. Progress with Magnetic Confinement Fusion
JET and the similar large Tokamaks in:
USA Tokamak Fusion Test Reactor (TFTR) Doublet IIID Tokamak (DIIID)
Japan Japanese Tokamak – 60U (JT-60U)
Have made significant progress in:
Technology of fusion;
Approaching the conditions of an Ignited plasma;
Predicting the behaviour of a reactor plasma;
Controlling impurities which enter the plasma
Operating with Tritium fuel

22. Progress towards Ignition
The Fusion Triple Product (PitE = niTitE) required to reach ignition can be compared with leading edge performance of the devices year-on-year.
The best plasmas now need an improvement of only 6 in performance. This requires a new larger device.

23. Controlling Impurities
Fuel Impurities are a major threat to reactor success
Two primary sources of impurities exist:
Helium “ash” from the fusion reaction
Material impurities from plasma-wall interactions
Impurities must be controlled since they:
Radiate energy, and reduce the plasma temperature
Dilute the fuel, thereby preventing ignition
The “Magnetic Divertor” is a device for controlling impurities. This has been tested successfully in JET.
Three different concepts have been compared.
Results agree with code predictions.

24. Progress with Magnetic Confinement Fusion
Pumped Divertor in JET
Impurities (C, Be) are produced by ion impact on target and are ionised in the plasma and returned to target

25. Fusion Power Development
The diagram encompasses :
Two pulses with 10% T in D in JET in 1991;
A result from the D-T studies on TFTR (1993 to 1997);
High fusion power and quasi-steady-state fusion power from the >200 pulses with >40% T in D in the JET D-T experiments of 1997.

27. ITER Design - Main Features
Central Solenoid
Blanket Module
Vacuum Vessel
Outer Intercoil Structure
Cryostat
Toroidal Field Coil
Port Plug (IC Heating)
Poloidal Field Coil
Divertor
Machine Gravity Supports
Torus Cryopump

28. ITER Objectives Programmatic Technical
Demonstrate the scientific and technological feasibility of fusion energy for peaceful purposes.
Technical
Demonstrate extended burn of DT plasmas, with steady state as the ultimate goal.
Integrate and test all essential fusion power reactor technologies and components.
Demonstrate safety and environmental acceptability of fusion.

29. ITER Parameters Total fusion power 500 MW (700MW)
Q = fusion power/auxiliary heating power ≥10 (inductive)
Average neutron wall loading MW/m2 (0.8 MW/m2)
Plasma inductive burn time ≥ 300 s
Plasma major radius m
Plasma minor radius m
Plasma current (inductive, Ip) 15 MA (17.4 MA)
Vertical flux surface/separatrix 1.70/1.85
flux surface/separatrix 0.33/0.49
Safety flux surface 3.0
Toroidal 6.2 m radius T
Plasma volume m3
Plasma surface m2
Installed auxiliary heating/current drive power 73 MW (100 MW)

31. ITER Site Layout

32. ITER Location
Caradache (France)
Rokkasho (Japan)

33. Fusion Nuclear Technology (FNT)
Fusion Power & Fuel Cycle Technology
FNT Components from the edge of the Plasma to TF Coils (Reactor “Core”)
1. Blanket Components
2. Plasma Interactive and High Heat Flux Components
a. divertor, limiter
b. rf antennas, launchers, wave guides, etc.
3. Vacuum Vessel & Shield Components
Other Components affected by the Nuclear Environment
4. Tritium Processing Systems
5. Instrumentation and Control Systems
6. Remote Maintenance Components
7. Heat Transport and Power Conversion Systems

34. Coolant for energy conversion Magnets
Shield
Blanket
Vacuum vessel
Plasma
Radiation
Neutrons
First Wall
Coolant for energy conversion
Magnets
Tritium breeding zone

35. Blanket (including first wall)
Blanket Functions:
Power Extraction
Convert kinetic energy of neutrons and secondary gamma-rays into heat
Absorb plasma radiation on the first wall
Extract the heat (at high temperature, for energy conversion)
Tritium Breeding
Tritium breeding, extraction, and control
Must have lithium in some form for tritium breeding
Physical Boundary for the Plasma
Physical boundary surrounding the plasma, inside the vacuum vessel
Provide access for plasma heating, fueling
Must be compatible with plasma operation
Innovative blanket concepts can improve plasma stability and confinement
Radiation Shielding of the Vacuum Vessel

36. Blanket Materials Tritium Breeding Material (Lithium in some form)
Liquid: Li, LiPb (83Pb 17Li), lithium-containing molten salts
Solid: Li2O, Li4SiO4, Li2TiO3, Li2ZrO3
Neutron Multiplier (for most blanket concepts)
Beryllium (Be, Be12Ti)
Lead (in LiPb)
Coolant
– Li, LiPb – Molten Salt – Helium – Water
Structural Material
Ferritic Steel (accepted worldwide as the reference for DEMO)
Long-term: Vanadium alloy (compatible only with Li), and SiC/SiC
MHD insulators (for concepts with self-cooled liquid metals)
Thermal insulators (only in some concepts with dual coolants)
Tritium Permeation Barriers (in some concepts)
Neutron Attenuators and Reflectors

38. A Helium-Cooled Li-Ceramic Breeder Concept: Example
Material Functions
Beryllium (pebble bed) for neutron multiplication
Ceramic breeder (Li4SiO4, Li2TiO3, Li2O, etc.) for tritium breeding
Helium purge (low pressure) to remove tritium through the “interconnected porosity” in ceramic breeder
High pressure Helium cooling in structure (ferritic steel)
Several configurations exist (e.g. wall parallel or “head on” breeder/Be arrangements)

39. Li/Vanadium Blanket Concept
Breeding Zone
(Li flow)
Primary Shield
Secondary Shield
Reflector Li
Secondary shield
(B4C)
Primary shield (Tenelon)
Lithium
Vanadium structure

40. Flows of electrically conducting coolants will experience complicated magnetohydrodynamic (MHD) effects
What is magnetohydrodynamics (MHD)?
Motion of a conductor in a magnetic field produces an EMF that can induce current in the liquid. This must be added to Ohm’s law:
Any induced current in the liquid results in an additional body force in the liquid that usually opposes the motion. This body force must be included in the Navier-Stokes equation of motion:
For liquid metal coolant, this body force can have dramatic impact on the flow: e.g. enormous MHD drag, highly distorted velocity profiles, non-uniform flow distribution, modified or suppressed turbulent fluctuations

41. Large MHD drag results in large MHD pressure drop
Conducting walls
Insulated wall
Lines of current enter the low resistance wall – leads to very high induced current and high pressure drop
All current must close in the liquid near the wall – net drag from jxB force is zero
Net JxB body force p = cVB2 where c = (tw w)/(a )
For high magnetic field and high speed (self-cooled LM concepts in inboard region) the pressure drop is large
The resulting stresses on the wall exceed the allowable stress for candidate structural materials
Perfect insulators make the net MHD body force zero
But insulator coating crack tolerance is very low (~10-7).
It appears impossible to develop practical insulators under fusion environment conditions with large temperature, stress, and radiation gradients
Self-healing coatings have been proposed but none has yet been found (research is on-going)

42. Dual Coolant Concept Designs from EU and USA
Cross section of the breeder region unit cell
(ARIES)

43. Summary The D-T Fusion process offers the promise of:
Virtually unlimited energy source from cheap abundant fuels;
No atmospheric pollution of greenhouse and acid rain gases;
Low radioactive burden from waste for future generations.
Tremendous Progress has been achieved over the past decades in plasma physics and fusion technology.
Fusion R&D involves many challenging areas of physics and technologies and is carried out through extensive international collaboration
EU,J, USA, RF, PRC, Korea are about to construct ITER to demonstrate the scientific and technological feasibility of fusion energy (ITER will produce 500MW of fusion power and the project total cost is about $15B)