Introduction to Fusion Energy Jerry Hughes IAP @ PSFC January 8, 2013 Acknowledgments: Catherine Fiore, Jeff Freidberg, Martin Greenwald, Zach Hartwig, Alberto Loarte, Bob Mumgaard, Geoff Olynyk Presenter’s e-mail: [email protected] Questions to answer • What is fusion? • Why do we need it? • How do we get it on earth? • Where do we stand? • Where are we headed? What is fusion, anyway? What is fusion, anyway? What is fusion, anyway? What is fusion, anyway? Fusion is a form of nuclear energy E mc2 • A huge amount of energy is released when isotopes lighter than iron combine to form heavier nuclei, with less final mass • It is an ubiquitous energy source in the universe • It is not (yet) a practical energy source on earth Fusion is a form of nuclear energy E mc2 • A huge amount of energy is released when isotopes lighter than iron combine to form heavier nuclei, with less final mass • It is an ubiquitous energy source in the universe • It is not (yet) a practical energy source on earth Terrestrial energy sources have their origin in the nuclear fusion reactions of stars Supernova produces radioactive elements Solar heating of the Earth drives atmospheric circulation, water cycle Sun illuminates Earth Terrestrial energy sources have their origin in the nuclear fusion reactions of stars Geothermal Decay of radioactive particles generates heat in Earth’s interior Nuclear fission Supernova produces radioactive elements Splitting radioactive particles generates heat Solar heating of the Earth drives atmospheric circulation, water cycle Sun illuminates Earth Terrestrial energy sources have their origin in the nuclear fusion reactions of stars Geothermal Decay of radioactive particles generates heat in Earth’s interior Nuclear fission Supernova produces radioactive elements Splitting radioactive particles Wind Atmospheric generates heat circulation turns Solar heating of the turbines Hydroelectric Earth drives atmospheric circulation, water Running cycle water turns turbines Sun illuminates Earth Terrestrial energy sources have their origin in the nuclear fusion reactions of stars Geothermal Decay of radioactive particles generates heat in Earth’s interior Nuclear fission Supernova produces radioactive elements Splitting radioactive particles Wind Atmospheric generates heat circulation turns Solar heating of the turbines Hydroelectric Earth drives atmospheric circulation, water Running cycle water turns turbines Solar Absorption of light for electricity generation Sun illuminates Biomass Earth Burn ‘em Photosynthesis generation of biomass Fossil fuels What are the prospects for nuclear fusion on Earth? • Scientists demonstrated BOMB = its use as a weapon in 1952 • For 50 years, scientists and engineers have been working create controlled nuclear fusion in the laboratory in order to exploit the fusion reaction as a practical energy source. What are the prospects for nuclear fusion on Earth? • Scientists demonstrated BOMB = its use as a weapon in 1952 • For over 60 years, scientists and engineers have been working create controlled nuclear fusion in the laboratory in order to exploit the fusion reaction as a practical energy source. REACTOR = Why do we need fusion? Earth-dwellers want to consume more energy . a lot more What Are The World’s Energy Options? Nothing obviously easy ● Burning fossil fuels (currently 80%) even if there was enough, must contend with climate change + pollution: is large-scale CO2 capture and storage feasible? ● Nuclear fission – safety, proliferation concerns (but cannot avoid if we are serious about reducing fossil fuel burning; at least until fusion available) ● Biofuels – can this be made carbon neutral? Land and water use issues ● Solar - need breakthroughs in production and storage ● Wind, Tidal – storage and land use issues, but could fill niche 18 Pros and Cons of Fusion Pros • Abundant, high energy density fuel (D + Li) • No greenhouse gases (nor NOX, SOX, particulate emission) • Safe – no chain reaction, ~1 sec worth of fuel in device at any one time • Minimal “afterheat”, no nuclear meltdown possible • Residual radioactivity small; products immobile and short-lived • Minimal proliferation risks • Minimal land and water use • No seasonal, diurnal or regional variation – no energy storage issue Cons • It doesn’t work yet (turns out to be a really hard problem) • Capital costs will be high, unit size large (but with low operating costs) 19 Fusion, like all nuclear energy, produces a tremendous amount of 7 energy from a very small mass of reactants. • Typical energy scales for chemical bonds – electron-volts (eV) • Typical energy scales for nuclear reactions – millions of electron-volts (MeV) (E=mc2) • This means that a gigawatt-class fusion power plant will use about a pickup truck full of fuel (lithium and deuterium) per year. • Compare to a 1 GWe coal plant – nearly 8,000 3 days worth of coal supply tons of coal per day! for a 500 MWe plant Fusion plants would have reduced environmental impact 27 relative to many renewables Wind, Solar, Hydro: substantial changes to the landscape needed to generate the first gigawatt Wind, Solar: lacking an energy storage solution How do we get controlled nuclear fusion on Earth? Back to the Future (“Mr. Fusion”) We’re not quite to this point yet . Spider-Man II SPF 35,000,000,000, anyone? How do we really get controlled nuclear fusion on Earth? Two types of nuclear reactions: • Fission – split heavy nuclei • (e.g. Uranium) • Fusion – fuse light nuclei • (e.g. hydrogenic isotopes) 26 The most energetically favorable fusion reaction is between deuterium (D) and tritium (T) 1 • Neutron : 0n 80 % of reaction energy ==> Not Confined ==> Energy output and tritium production 4 •Alpha particle : 2He 20 % of reaction energy ==> Confined ==> Plasma Self Heating D + T → He + n + 17.6 MeV 27 Fuel Supply - Fusion • Plenty of D from the ocean • No natural T – half life = 12 years • Need to breed T in the reactor Li-6 + n → He + T + 4.8 MeV • Li-6 is 7% of natural lithium • 1000’s of years of natural lithium Fuel for a fusion power plant: 30 t/day seawater 350 kg/yr lithium (extract deuterium) (breed to tritium) 28 Problem: Nuclei do not play well together • Like charges repel (Coulomb force) + + • Throw them at each other and they tend to scatter • Huge energies are needed to overcome this repulsive force 29 Problem: Nuclei do not play well together • Like charges repel (Coulomb force)+ + • Throw them at each other and they tend to scatter • Huge energies are needed to overcome this repulsive force 30 The Probability Of D-T Fusion Is The Greatest When The Nuclei Have About 100 Kev Of Kinetic Energy • Even at the optimum energy, the nuclei are much more likely to scatter elastically than to fuse! • Therefore, nuclei must be confined over numerous scattering times this puts the fuel into a thermodynamic equilibrium • Significant fusion rate requires fuel to be confined at >100 million degrees! 31 At the high temperatures required for the fusion reaction, 10 the deuterium and tritium are in the plasma state. • When energy is added to matter, phase changes can occur new physical properties. • When sufficient heat energy is Add heat added to matter, bound electrons strip from the nuclei • Plasma = “soup” of negatively charged electrons and positively charged nuclei. At the high temperatures required for the fusion reaction, 10 the deuterium and tritium are in the plasma state. • When energy is added to matter, phase changes can occur new physical properties. • When sufficient heat energy is Add heat added to matter, bound electrons strip from the nuclei Solid / liquid / gas Plasma e– e– Neutron • Plasma = “soup” of negatively Proton charged electrons and e– e– positively charged nuclei. At the high temperatures required for the fusion reaction, 10 the deuterium and tritium are in the plasma state. • When energy is added to matter, phase changes can occur new physical properties. • When sufficient heat energy is Add heat added to matter, bound electrons strip from the nuclei Solid / liquid / gas Plasma e– e– Neutron • Plasma = “soup” of negatively Proton charged electrons and e– e– positively charged nuclei. In plasma physics, we measure temperature in eV, where 1 eV = 11,600 K Typical fusion plasma temp = 10 keV 100 million degrees Most of the visible universe is composed of plasma . not all of it is fusing 35 High confinement is needed for plasma fusion • Our goal: get the required temperature with the least amount of heating power • Energy confinement time is the ratio of stored energy to heating rate. • In a fusion reactor that heat would come from the fast a particles (charged, so they are confined by the magnetic field) Total stored energy (Joules) (sec) E Heating rate (Watts) “Fuse it or lose it.” 36 Conditions needed for a self-sustaining fusion plasma 20 3 • We need enough plasma: nm 10 (air/100,000) • At a high enough temperature: T 15 keV (air x million) • Holding its heat for a long enough time: 2sec • For a sustained fusion plasma – Lawson Criterion 21 n T τE ≥ 3x10 p 8 atm sec [keV s m−3] 37 A complete power plant will need to satisfy Lawson criterion, breed tritium and collect heat to drive turbines to actually make electricity and put it on the grid. Lithium compound 38 How do we hold together a hot dense plasma? Approaches To Fusion Energy • Gravitational Confinement (300 W/m3) – In a deep gravitational well, even fast particles are trapped. 6 – Very slow: E ~ 10 years, burn-up time = 1010 years ● Inertial Confinement (1028 W/m3) – Heat and compress plasma to ignite plasma before constituents fly apart. – Like a little H-bomb – Capsules would need to be burned with high gain, high rep rate for reactor practicality ● Magnetic Confinement (107 W/m3) – Uses the unique properties of ionized particles in a magnetic field 40 Gyro-motion Of Charged Particles Enables Magnetic Confinement, perpendicular to B-field Ionized particles are deflected by the Lorentz force and bent into circular orbits.