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Nuclear Fusion : Using the energy of the stars on Earth. The Principle. Collision : Deuterium and Tritium. How is it made ?. In Stars: The gravity pressure makes the atoms close enough for the fusion . The high temperatures keep the plasma state making the collisions easier .
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How is it made? • In Stars: Thegravitypressure makestheatoms close enough for thefusion. Thehightemperatures keepthe plasma statemakingthe collisionseasier. • OnEarth: The super gravityofthe stars can’tbereproduced, sothetemperaturemustberisen a lot, aboutten times thesun’scenter. Theatomswill move sofastthecollisionandfusionwillhappen.
TheProcess • Exactlytheoppositeofthe conventionalfissionenergy, with some advantages over it: theradioactive nuclear wastehaslowintensityand vanish in a fewyears, beyondthat, there’s no risk ofdisasters • As thefission, represents no harm for thenature
Whyit’snotused? • No nuclear reactoruntilnowhasmade it to produce more energythantheneeded for its running. • Thefirstprototypewith chance to achievethisgoal is the ITER (InternationalThermonuclear Experimental Reactor) which is being build in France sincelastyear.
Difficulties - ITER • Thedifficulties start withthe lackoftritiumonearth, it’s estimatedthatthere are only 20 Kg ofthisisotope. • The solution foundwasput the machine itself to produce it, theywilltry to use lithium, oncewhenthe energizedneutron hits it, tritium is liberated.
ITER - Temperature • Three systems willbeused to reachtherequiredtemperature: • First neutral particles are injected in highspeed • Thesecondwillemit radio waves in differentfrequencies,similar to micro-wavesovens • Andthethirdwill use a beamofeletromagneticradiation to make hot theelectronsinsidethe machine.
Keepingthetemperature • However, noneofthiswill work ifthe plasma touch theinternalstructureofthe machine. The trade of heatbetweenthewalland thehydrogenwouldcold thelastone, stoppingthe wholeprocess • That’swhy it represents no risk, ifanythingfailsthe machine turns off.
ITER • Thereactormodel to avoidthis contactused in ITER is called ‘tokamak’.It’susednowadays in JET, thereactorthatwasused as a base for ITER’sproject. • It hastheshapeof a tyre, withvacuumand a strongmagneticfield, 200 000 times theearth’sone. • Thiswillkeepthe plasma farfromthestructurewalls
Alternativesoffusion • In USA wehavetwoinertial fusionreactors: • The laser beams, where 192 laser beams hit a small ball the size of a pea, fusing the atoms inside. • Electrical chock used in the Z machine: electrical discharges of high power to make the fusion
Alternativesoffusion • And the Stellarators, in Japan, who works as the tokamaks, the difference is in the spiral shape which distributes better the magnetic field.
Future • ITER willbeready in 8 years time, it’sexpected to producetentimes more energythan it consumes. • If it succed ,theprojectof Demo, thefirstfusionreactorwithcommercialgoals, will start, it’spredicted to beoperating in 2040.