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Freudenstadt 10 th October 2007

The roadmap for nuclear fusion A. M. Bradshaw. Freudenstadt 10 th October 2007. G8 Summit Heiligendamm: CHAIR'S SUMMARY. Climate Change, Energy Efficiency and Energy Security:

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Freudenstadt 10 th October 2007

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  1. The roadmap for nuclear fusion A. M. Bradshaw Freudenstadt 10th October 2007

  2. G8 Summit Heiligendamm: CHAIR'S SUMMARY Climate Change, Energy Efficiency and Energy Security: Combating climate change is one of the major challenges for mankind and it has the potential to seriously damage our natural environment and the global economy. We noted with concern the recent IPCC report and its findings. We are convinced that urgent and concerted action is needed and accept our responsibility to show leadership in tackling climate change. Change in mean annual temperature: Estimated for 2071-2100 relative to 1961-1990, IPCC report, scenario A2. (Here: Fig. 1 in „GREEN PAPER 2007“)

  3. Four important questions In view of anthropogenic climate change caused by excessive use offossil fuels and dwindling reserves we can ask the following questions: • Will renewable energies be able to replace fossil fuels? • Will politicians be able to persuade an unwilling – or perhaps ill-informed – population to use less energy ? • Can public confidence in nuclear fission be restored? • Can nuclear fusionas a potential sustainable energy source makea significant contribution to the energy supply in this century?

  4. Edward Teller (1959): “I believe it is extremely important that work on controlled nuclear fusion continue because the end result is valuable and its eventual achievement is probable. Maybe it will be the year 2000, maybe it will be even later.” Fusion: the so-called moving target

  5. The roadmap for nuclear fusion • Nuclear fusion – an inexhaustible source of energy • Magnetic confinement • No fusion without large experiments • ITER – on the way to a fusion power plant

  6. 10 16O 56Fe 12C 238U 8 9Be 4He 6 B 10 Fission 6Li 4 3T Fusion 3He 2 2D n, 1H 0 10 100 1 Two ways to utilise nuclear forces Binding energy per nucleon Binding energy [MeV/A] Mass number A Fusion of light elements releases energy as does splitting of heavy elements – Fission.

  7. Fusion – overcoming the Coulomb force Deuterium- Tritium • As the number of nucleons increases, the Coulomb repulsion between the nuclei also increases. • Reaction rate depends on tunnelling probability, exp{-Z2/Erel} • Fusion reaction: light nuclei with high relative velocity (high T, plasma)

  8. Fusion – the energy source of the stars The sun radiates 1026 Watt and may be considered as a huge power plant. The energy source is the fusion of hydrogen nuclei to helium: Gravity provides the necessary “confinement” in the sun. p + p  D + e+ +  D + p  3He +  3He + 3He  4He + 2 p ----------------------------------------------------- 4 p  4He + 2 e+ + 2  + 26,7 MeV 1026 Watt

  9. Fusion on earth – the appropriate reaction • Reaction probability for DD and DT reactions much higher than for p-p. • A DT plasma is the likely candidate for a fusion power plant • Problems:─ high temperatures (> 100 Mio oC) ─ T is radioactive: t1/2 = 12,3 years,→ T not readily available; will have to be bred in situ from lithium

  10. Deuterium p p p p Neutron Fusion n n n n n n Helium(4He) Tritium AxKa20060821 Fusion on earth – properties • Energy is mainly transported by the neutrons. Problem: Activation of materials. • Resources available for millions of years: - D from water: D:H = 1:7000,- T breeding inside 6Li + n 4He + T • Confinement of the hot plasma by magnetic field • Alternative: inertial confinement D + T 4He + n + 17,6 MeV

  11. The roadmap for nuclear fusion • Nuclear fusion – an inexhaustible source of energy • Magnetic confinement • No fusion without large experiments • ITER – on the way to a fusion power plant

  12. ion electron magnetic field Magnetic confinement I: Lorentz force • Lorentz force: charged particles move on spiral orbits along magnetic field lines. • Particle transport perpendicular to the magnetic field B occursonly via collisions. • Unhindered movement parallel to B leads to losses of particlesin a linear field geometry. • Solution: Bend the magnetic field to a torus !

  13. Magnetic confinement II: E x B - drift • Curvature and inhomogeneity of a purely toroidal field result in→ electrons and ions movements in opposite directions, i.e. →charge separation→ electric field E. • A resulting E x B drift causes the whole plasma to moveout of the torus. • Solution: Twist the field lines!

  14. Magnetic confinement III: Twisting the field lines Magnetic field lines Magnetic flux surfaces There are two competing concepts for twisting the field lines, StellaratorsandTokamaks.

  15. Magnetic confinement IV: Tokamak versus Stellarator Tokamak Stellarator ASDEX Upgrade, Garching WENDELSTEIN 2-A, Deutsches Museum

  16. The Stellarator • Lyman Spitzer, 1950, Princeton. • Helical external coils provide a poloidal field component which twists the field lines as required. Advantages+ only external fields+well controllable+ stationary operation • Disadvantages- nested coils- poor confinement of particles •  Optimisation •  Modular Stellarators

  17. WENDELSTEIN 7-X – the forthcoming stellarator experiment R = 5.5 m a = 0.53 m Bt = 3 T WENDELSTEIN 7-X is • a modular, quasi-symmetric stellarator • completely optimised with numerical methods • under construction at the IPP branch institute at Greifswald – operational in 2014 In the plasma vessel of W7-X

  18. WENDELSTEIN 7-X: Plasma Radius: 5.5 m Mean minor radius: 0.53 m

  19. WENDELSTEIN 7-X: Plasma vessel Volume: 110 m3 Surface: 200 m2Mass: 35 t Vacuum: 1…2 · 10–8 hPa

  20. WENDELSTEIN 7-X: Superconducting coils 50 non-planar coils & 20 planar coils Superconductor: NbTi (> 3.4 K) Flux density, on axis: 2.5 T Flux density, at coil: 6.8 T @ 17.8 kA

  21. WENDELSTEIN 7-X: Cryostat Volume: 525 m3 Surface: 480 m2 Vacuum: < 10–5 hPa Mass: 150 t

  22. The Tokamak • Artsimovitch and Sacharow, Moscow Russian acronym for „Toroidalnayakamera s Magnitnymi Katushkami“(Toroidal chamber with magnetic field) • Plasma is the secondary coil of a transformer, so that a toroidal current is induced. • The plasma current gives rise to a poloidal magnetic field and thus to helical net field which “winds” around the plasma. • The current also heats the plasma. • Problems • - pulsed operation (transformer … ) • - instabilities

  23. ASDEX Upgrade – a major Tokamak experiment Major radius = 1,65 m, Bt 3,5 T minor radius = 0,5 m, Ip 1,4 MAPH 28 MW,  = 1.6 Start of operation in 1991; here: during construction in 1989

  24. Tokamak – inside ASDEX Upgrade

  25. Plasma-wall interactions Tritium retention in ITER depending on first wall material (C versus W) co-deposition viaerosion of C in W via implantation ASDEX Upgrade: First tungsten machine

  26. First wall materials – tungsten • Accidental loss of coolant: peak temperatures of first wall up to 1200 °C • If contact with air takes place: formation of highly volatile WO3 compounds • Evaporation rate: order of 10-100 kg/h at >1000°C in a reactor (1000 m2 surface) • → a large fraction of radioactive WO3 may leave hot vessel → Need for development of self-passivating tungsten alloys!

  27. WSi10Cr10: (4.5 µm) WSi11: (1.5 µm) Resin Tungsten: (1.5 µm) Cr2O3 Oxidation rate (mg cm-2 s-1) W, Si, WO3, SiO2 W-Si-Cr alloy 5 5 µ µ m m Sapphire substrate First wall materials – self-passivating tungsten-based alloys Results of thermo-balance measurements (synthetic air) • Synthesis of tungsten-based films by sputter deposition • Thermogravimetric measurements of oxidation behavior at different temperatures in synthetic air Oxidation rate has been calculated from weight in-crease versus time. Compositions are given in wt.%. Formation of protective oxide layers, reduction of oxidation rate by a factor of 5000 compared to pure tungsten! Cross section of of W-Si-Cr film after oxidation at 1000 °C for 1h. Freimut Koch

  28. The roadmap for nuclear fusion • Nuclear fusion – an inexhaustible source of energy • Magnetic confinement • No fusion without large experiments • ITER – on the way to a fusion power plant

  29. break even Fusion product Fusion product nTE n - density T - temperature E - energy confinement time E= Wplasma/Pheating nTE> 5*1021 m-3 keV s • Power amplification Q = Pfus/Pext • Q = 1 „break-even“ • Q = 20…50 typical for a power plant • Q = ∞ ignition Ignition Heating by -particles > Loss (radiation, transport)

  30. Champion: Joint European Torus (JET), Culham/Oxford To improve the confinementwe need a large experiment! Source: JET

  31. What we have reached so far • Values reached in different experiments: • temperature T 400 Mio.°C  • density n 1020 m-3  • energy confinement time E ~1,5 s, which is still too short! • ITER: Due to the larger volume, and thus a longer E, a power amplification factor of Q ≥ 10 is expected! ITER: Pfus = 500 MW, major radius = 6.2 m,minor radius = 2.0 m Why is this the case?

  32. B     transport to the edge Energy confinement and transport I: „classical ansatz“ Simple (classical) ansatz: • Diffusion due to collision , D  0.0001 m2/s (: Heat transport coefficient) The transport of energy determines the energy confinement time tE . E ~ a2/ (: heat transport coefficient, a: minor radius) collision Provided that the classical ansatz is an appropriatedescription of the energy transport …g a Tokamak with a ≈ 2 cm should ignite!

  33. Energy confinement and transport II: „neoclassical ansatz“ • The particles in the magnetic field are trapped on „banana orbits“ • Diffusion is defined by thewidth of the „banana orbits“ • , D  0.01 m2/s Modified (neoclasscal) ansatz: Inhomogeneities in the magnetic field are observed • A Tokamak with a ≈ 20 cm should ignite!

  34. Energy confinement and transport III: empirical Not even the „neoclassical ansatz“ is sufficient to describe energy transport. Experimental result: Turbulent (anomalous) transport: , D  1 m2/s Variation of ion temperature ASDEX Upgrade • A Tokamak with a ≈2 m will ignite!

  35. Internal transport barriers ( continuous operation?) “Improved” H-mode ( extended operational regime for ITER; discovered at ASDEX Upgrade) Druck H-mode: Transport barrier at plasma edge ( current ITER standard scenario; discovered at ASDEX) 0 1 r / a Confinement improvement by suppressing turbulance

  36. Advanced confinment by enlarged experiments ASDEX Upgrade JET ITER x 2 → x 2 → , growing in size • similar in shape

  37. The roadmap for nuclear fusion • Nuclear fusion – an inexhaustible source of energy • Magnetic confinement • No fusion without large experiments • ITER – on the way to a fusion power plant

  38. (… 1999; 2003) (2003) (2003) (2005) Joint work sites: Garching, Naka, San Diego ITER location: Cadarache 28th June 2005:“… ITER shall be sited at Cadarache.” Source: www. iter.org; www.bundesbank.de ITER 2001: 5 bn € Pfus = 500 MW, major radius = 6.2 mminor radius = 2.0 m

  39. ITER – the feasibility of fusion power Physics goals: • Demonstrate an energy producing (“burning”) plasma where the α-particles emitted by the fusion reaction are the dominat heat source (Q ≥ 10). • Reach stationary conditions with non-inductive current drive (Q > 5). • Testing “advanced tokamak scenarios” (Q = ∞, ignition not excluded) Technology goals:availability and integration of essential technologies, e.g. • Superconductivity and cryogenics • High heat flux and radiation-resistant components • Remote handling • Fuel technology (tritium cycle) • Plasma heating and current drive systems

  40. Roadmap to a fusion power plant Plasma physics Tokamak physics Stellarator physics (WENDELSTEIN 7-X) Facilities ITER DEMO IFMIF: 14 MeV neutron source Technologies First electricalpower production First commercialfusion power plant ITER relevant technologies DEMO relevant technologies 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

  41. The fusion power plant … and its characteristics • Intrinsic energy/forces (thermal energy, magnetic field, chemical inventory)unperilous for containment • Investment costs for sophisticated technology dominant – negligible fuel costs • Closed tritium cycle • No radioactive primary fuels • 100 years after shutdown materials are completely recyclable→no „permanent disposal waste“ • Primary energy carrier (D and Li) available all over the world !!!

  42. Conclusion How long will it take? “Fusion will be ready when society needs it.”Lev Andreevich Artsimovich, 1909 – 1973.

  43. Reserve

  44. Primary energy supply worldwide – and in Germany <1% others * combustible renewables & waste 11% hydro 2% 24% coal nuclear 7% Source: IEA – Key World Energy Statistics 2005 natural Gas 21% 34% oil Total primary energy supply in 2003: 10,6 Gtoe = 443 EJ = 123 000 bnkWh Germany: 4 000 bn kWhper person and day: 132 kWh * others: geothermal, solar, wind etc.

  45. The end of fossil fuels – oil Source: BGR, 2003

  46. Renewable energies worldwide primary energy consumption today Will renewable energiesbe able to replace fossil fuels? sun wind biomass water geothermal energy Source: DLR technical versus theoretical potential of renewable energies

  47. ITER – a long “way” • 1985, Geneva Summit: Gorbachov suggests to Reagan that the next large fusion experiment be built together with Europe and Japan. • 1988: Joint “Conceptual Design” starts at IPP in Garching. • 1992: “Engineering Design Activities”, three “Joint work sites”: Garching, Naka (Japan) and San Diego. • 1998: ITER proposal (at the right). USA withdrawal. • 2001: Re-design of a cheaper and technically less ambitious version results in the current ITER design. • 2001-2005: Negotiations on project and site.2003: China and South Korea join, USA rejoin. Site stand-off between Japan and Europe. ITER proposal 1998: 10 bn € Pfus = 1500 MW, R = 8.1 m

  48. Fusion power: The SUN versus ITER pp-reaction Type DT-reaction gravitation Confinement magnetic field 1.4 ·109 m Diameter 30 m150 g/cm3Density 4 ·10-10 g/cm3 1.5 ·107 °C Temperature 1.5 ·108 °C 1026WthPower 5 ·108 Wth 200 Wth/m3Power density106 Wth/m3

  49. Nicht-monotones Stromprofil Turbulenzunterdrückung hohe Druckgradienten großer bootstrap-Strom Stationäres Tokamak-Szenario • HF-Wellen • NBI

  50. Radiotoxicity of the waste materials Radioactive waste due to • contamination with tritium (t1/2 = 12,3 years) • materialsactivation by the intensive flux of high energy neutrons Main topic for materials researchis to minimise materialsactivation by an appropriate choice of materials compounds.→ recycling is possible after a temporary storage for 100 years.→ no „permanent disposal waste“ Source: Safety and Environmental Impact of Fusion (SEIF 2001) Recycling possible

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