Nuclear Fusion 



All matter, whettier it be solid, liquid or gas. is made of tiny 



particles called atoms At the centre of every atom is a 



positively ctiarged nucleus around whicti orbit a number of 



smaller negatively ctiarged particles called electrons 



If tfie nuclei of the lightest elements can be made to |Oin or 



fuse together to form heavier ones then large amounts of 



energy are released 



This IS the process called nuclear fusion, from which the sun 



and stats derive their energy 



For fusion reactions to occur, the fuels, vi/hich are gases. 



must be heated to very high temperatures As the gases 



are heated, the atoms become ionized, le the electrons 



which are orbiting around the nucleus become free This 



mixture of randomly moving electrons and nuclei is called 



PLASMA 



At plasma temperatures around 100 million °C abundant 

 fusion reactions occur betv^een deuterium and tritium nuclei 

 These tvi/o gases v^rhich are different forms of hydrogen 

 would be used in the first fusion reactors. 



JET-The Principles 



As plasma is a mixture of positive and negative particles, 

 magnetic fields can be used to contain it and so prevent the 

 particles hitting the wall of the containing vacuum vessel 

 During the operation of the JET experiment, a small quantity 

 of gas IS introduced into the doughnut-shaped vacuum 

 vessel-the Torus The gas is healed to form a plasma by 

 passing a large electric current through il This plasma 

 current, of up to 5 million amperes (5 MA), also produces a 

 magnetic field (poloidal) which combines with a second field 

 (toroidal) produced by 32 D-shaped coils equally spaced 

 around the vacuum vessel The combination of these two 

 magnetic fields provides the cage that prevents the hot 

 plasma from hitting the walls of the vacuum vessel This 

 complex system of magnetic fields is called a TOKAMAK, a 

 Russian acronym lor toroidal magnetic chan.ber 

 A set of SIX hoop coils around the outside of the machine 

 produces the magnetic field that shapes and positions the 

 plasma centrally in the torus. 



Water contains deutenum and therefore there is a plentiful 

 supply of this fuel Tritium does not occur naturally and 

 must be manufactured from lithium of which there are large 

 resen/es in the earths crust 



The fusion of deuterium and tritium produces the heavier 

 helium nucleus, and a particle with no electrical charge 

 called a neutron Eighty percent of the energy released 

 during this reaction is given to the neutron, making it travel at 

 very high speed It is this energy that will be harnessed for 

 power generation 



:: field configuration 



Fusion Reactor 



If the work on JET and on future expenments is successful 

 then It will eventually lead to the building of a fusion reactor 

 In such a reactor the neutrons produced during the fusion 

 reactions would be captured by a blanket surrounding the 

 plasma region 



The blanket, which would contain lithium, would enable the 

 tntium needed for the reaction to be manufactured 

 The captured neutrons would heat up the blanket to 

 temperatures in the region of SOO'C so that steam could be 

 raised to drive turbines and generate electricity in the normal 

 manner. 



