Fusion: Basic Principles, Current Progress and ITER Plans 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 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 Energy Released by Nuclear Fusion and Fission Fusion reactions release much higher energies than Fission reactions Where does Tritium & Deuterium Come from? Tritium: Bombarding Lithium with a Neutron Deuterium: Plentiful in ordinary water. 1/6500 hydrogen atoms in water is Deuterium 1 gallon of water conceivably has the energy content of 300 gallons of gasoline Source: General Atomics Fusion Reactions Deuterium from water (0.02% of all hydrogen is heavy hydrogen or deuterium) Tritium from lithium (a light metal common in the Earths crust) Deuterium + Lithium Helium + Energy This fusion cycle (which has the fastest reaction rate) is of interest for Energy Production 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 Fusion8 Nuclear Fusion Cross Sections Cross sections data from reactions studied using particles from cyclotron 7 Li (p, n) 7 Be 3 T (p, n) 3 He 1 H (t, n) 3 He 2 D (d, n) 3 He 2 D (t, n) 4 He 3 T (d, n) 4 He Fusion9 Nuclear Fusion and Plasma Confinements fd3.gif from ippex.pppl.gov/ippex/module_5/see_fsn.html Three confinement methods Fusion10 Nuclear Fusion and Plasma - kinetic energy Kinetic energies of particles in plasma follow the Maxwell-Boltzmann distribution Fusion11 Nuclear Fusion and Plasma - particle motion Charged particles avoid crossing magnetic lines. Fusion12 Nuclear Fusion using Magnetic Plasma Confinement A plasma distorts magnetic field or bends magnetic lines. A Magnetic Bottle for Plasma Confinement Fusion13 Nuclear Fusion using Tokamak The Tokamak technology for plasma confinement in fusion fd4.gif200 pulses with >40% T in D in the JET D-T experiments of 1997. ITER Design - Main Features Divertor Central Solenoid Outer Intercoil Structure Toroidal Field Coil Poloidal Field Coil Machine Gravity Supports Blanket Module Vacuum Vessel Cryostat Port Plug (IC Heating) Torus Cryopump ITER Objectives Programmatic 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. ITER Parameters Total fusion power500 MW (700MW) Q = fusion power/auxiliary heating power10 (inductive) Average neutron wall loading 0.57 MW/m 2 (0.8 MW/m 2 ) Plasma inductive burn time 300 s Plasma major radius 6.2 m Plasma minor radius2.0 m Plasma current (inductive, I p )15 MA (17.4 MA) Vertical flux surface/separatrix1.70/1.85 flux surface/separatrix0.33/0.49 Safety flux surface3.0 Toroidal 6.2 m radius5.3 T Plasma volume837 m 3 Plasma surface678 m 2 Installed auxiliary heating/current drive power73 MW (100 MW) ITER Site Layout ITER Location Caradache (France)Rokkasho (Japan) Fusion Nuclear Technology (FNT) FNT Components from the edge of the Plasma to TF Coils (Reactor Core) 1. Blanket Components 2. Plasma Interactive and High Heat Flux Components 3. Vacuum Vessel & Shield Components 4. Tritium Processing Systems 5. Instrumentation and Control Systems 6. Remote Maintenance Components 7. Heat Transport and Power Conversion Systems a. divertor, limiter b. rf antennas, launchers, wave guides, etc. Other Components affected by the Nuclear Environment Fusion Power & Fuel Cycle Technology Plasma Radiation Neutrons Coolant for energy conversion First Wall Shield Blanket Vacuum vessel Magnets Tritium breeding zone Blanket (including first wall) Blanket Functions: A.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) B.Tritium Breeding Tritium breeding, extraction, and control Must have lithium in some form for tritium breeding C.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 D.Radiation Shielding of the Vacuum Vessel Blanket Materials 1.Tritium Breeding Material (Lithium in some form) Liquid: Li, LiPb ( 83 Pb 17 Li), lithium-containing molten salts Solid: Li 2 O, Li 4 SiO 4, Li 2 TiO 3, Li 2 ZrO 3 2.Neutron Multiplier (for most blanket concepts) Beryllium (Be, Be 12 Ti) Lead (in LiPb) 3.Coolant Li, LiPb Molten Salt Helium Water 4.Structural Material Ferritic Steel (accepted worldwide as the reference for DEMO) Long-term: Vanadium alloy (compatible only with Li), and SiC/SiC 5.MHD insulators (for concepts with self-cooled liquid metals) 6.Thermal insulators (only in some concepts with dual coolants) 7.Tritium Permeation Barriers (in some concepts) 8.Neutron Attenuators and Reflectors A Helium-Cooled Li-Ceramic Breeder Concept: Example Material Functions Beryllium (pebble bed) for neutron multiplication Ceramic breeder (Li 4 SiO 4, Li 2 TiO 3, Li 2 O, 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) Li/Vanadium Blanket Concept Breeding Zone (Li flow) Primary Shield Secondary Shield Reflector Li Secondary shield (B 4 C) Primary shield (Tenelon) Reflector Lithium Vanadium structure 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 Ohms 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 Large MHD drag results in large MHD pressure drop Net JxB body force p = c VB 2 where c = (t w 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) 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 Conducting wallsInsulated wall Dual Coolant Concept Designs from EU and USA Cross section of the breeder region unit cell (ARIES) 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) Two approaches to fusion One is based on the rapid compression, and heating of a solid fuel pellet through the use of laser or particle beams. In this approach one tries to obtain a sufficient amount of fusion reactions before the material flies apart, hence the name, inertial confinement fusion (ICF). Magnetic confinement.. The Lorentz force connected with a magnetic field makes that the charged particles can not move over large distances across the magnetic field They gyrate around the field lines with a typical radius At 10 keV and 5 Tesla this radius of 4 mm for Deuterium and 0.07 mm for the electrons