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Magnetic Fusion
One of the approaches considered to achieve fusion is to trap the plasma in a
magnetic field. The negative electrons and positive nuclei in the plasma will
spin around magnetic lines but diffuse only slowly across them. The best
magnetic machine loops the magnetic line into a doughnut shaped region. So the
particles spiral along the field line, go around the doughnut and cannot easily
escape. This arrangement is called a Tokamak.
The strongest magnetic field that can be generated using superconductor
magnets are limited by material issues. The plasma that can be confined by this
field is of low density so the fusion rate is low. The plasma and energy must
therefore be confined for many seconds to achieve break-even. Unfortunately,
many complex mechanisms cause some particles and energy to leak out of the trap.
Because the surface (where energy is lost) increases slower than the volume
(where fusion energy is created) for bigger plasmas, bigger machines have more
chances to break-even than smaller ones. This has pushed the researchers to
build bigger and bigger Tokamaks.
Today, the biggest Tokamak is the $1 billion JET (Joint European Torus) in
England.
www.jet.efda.org
It is not expected to reach break-even. However, the
science is now well understood and it is expected that a bigger machine would
actually produce energy. The next step is the ITER (International Tokamak
Experimental Reactor), a large, multibillion dollar machine.
www.iter.org
Because of the
complexity and cost, the power produced by ITER will be about ten times more
expensive than today's energy price. Because of this high price tag, many
countries are trying to join forces to build the ITER. So far, the budget has
not received approval.
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