|MadSci Network: Physics|
Fusion reactors will use energy released in nuclear fusion reactions, where light element nuclei are fused to form a heavier element nucleus. In that proccess, some amount of original nuclei mass is transformed into energy (remember E=mc2 ?). You can find a more detailed explanation of nuclear reactions on MadSciArchives (answers to questions 970785342.Ph, 853464363.Ph or 899578182.Ph.). About Fusion Reactors, it is important to state that there is no one working by now, after more than forty years and billions dollars spent. Nonetheless, there are thousands of scientists all over the World designing future reactors and running dozens of experimental machines to learn about nuclear fusion and reactors design (although none of them can actually produce energy). An hypothetical Fusion Reactor would work as actual Fission Reactors do. During a nuclear reaction some neutrons fly away from original nuclei, taking with them a portion of the energy released in that reaction. Those neutrons are slowed down, passing their kinetic energy to some coolant which results heated. Heat absorbed by the coolant is used to produce steam from water, which will later be used to move a turbine linked to an electric generator, producing electric energy in that way. That's the principle, and it looks simple. One of the main problems with fusion reactors design is that in order to obtain nuclear fusion the fuel to be used (hydrogen or its isotopes) must be at a temperature as high as 100 million Centigrade Degrees. As you can imagine any known material would result volatilized at a temperature one thousand times lower than this, so a reactor must be designed as to keep thermonuclear fuel away from its walls. There are two approaches to this idea. One of them is what is called ''Magnetic Confinement''. At such a high temperature as is needed to obtain fusion reactions, matter appears completely ionized. Charged particles (electrons and nuclei) can be trapped in a magnetic field, because a moving charged particle follows magnetic field lines. If you design a device where magnetic field lines don't cross the walls, charged particles will follow them and will never touch the walls, avoiding the risk of damaging them. Such a device has a vacuum hollow doughnut shaped chamber, and magnetic field lines go around it (and particles following them). Then fuel can be heated by any means (microwaves, neutral beams, ohmic heating ...) to reach nuclear fusion temperatures, and the reactor will then be working. There are two types of these devices: Tokamaks and Stellarators. Both are almost the same, and the main difference is that in Tokamaks nuclear fuel is heated and confined by driving an electric current through it (remember it is ionized, so it is an electric conductor) while in Stellarators no electric current is driven through the plasma (the name that is given to an ionized gas). The other approach to nuclear fusion reactors is ''Inertial Confinement''. An inertial confinement device consists in a vacuum chamber (usually spherical in shape) where small fuel pellets are injected, as if shooted by a gun. When those pellets reach the chamber's centre, extremely powerful laser or particle beams are shooted to it from all directions. Those beams make the pellet to be compressed and heated till a point where fusion reactions begins, with subsequent emission of neutrons. After the first pellet has been burned another one is shooted into the chamber, and the proccess continues. This is a rough view of fusion reactor designs. You can find much more information visiting the websites listed below. -> Magnetic Confinement: * Tokamaks: http://www.iter.org (International Thermonuclear Experimental Reactor - ITER. This is a project involving countries and scientists all around the World, to design and build the first reactor where ignition is expected to be reached.) http://www.jet.efda.org (Joint European Torus - JET. One of the largest tokamaks in the World. It has been running and producing many valuable scientific results for twenty years.) * Stellarators: http://www.ipp.mpg.de/ipp/ipp.eng.html (Max-Planck Institute for Plasma Physics. Germany. They have one of the two largest stellarators ever built: W7AX. Now they operate a smaller one: W7AS.) http://www.nifs.ac.jp/~LHDhp/homepage.html (Large Helical Device - LHD. Japan. The other largest stellarator ever built: LHD.) -> Inertial confinement: * Lasers beams: http://www.llnl.gov (Lawrence Livermore National Laboratory - USA. They have the World's largest and most powerful laser: NOVA) * Ion Beams: http://www.sandia.gov (Sandia National Laboratories - USA) You have some information about Nuclear Fusion at MadSci Archives. Search for ''Nuclear Fusion'' or ''Nuclear reactors'' using MadSci Search Engine. You can also surf through the following websites, and find all the information you want about nuclear fusion and plasma physics. * http://fusion.gat.com/PlasmaOutreach/ (Various USA Universities and Laboratories have developed a program called 'Plasma Sciences and Technologies Education Outreach' with the aim of getting ready a place to learn about Plasma Physics and Nuclear Fusion). * http://FusEdWeb.pppl.gov/ (Princeton University Plasma Physics Laboratory) * http://www.lbl.gov/abc/ (Lawrence-Berkeley National Laboratory. Here you have a site with introductory information about nuclear and particle Physics.) * http://www.ornl.gov/ (Oak Ridge National Laboratory, Tennessee. They work in nuclear fusion, fision and many more things ...) Enjoy, ... and keep on thinking.
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