Power of the Sun

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Power of the Sun
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• Conditions at the Suns core are extreme
• temperature is 15.6 million Kelvin
• pressure is 250 billion atmospheres
• The Suns energy out put (386 billion
  megawatts/sec) is produced by nuclear fusion
  reactions.

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Nuclear Fusion

• The process that unites small mass nuclei into
  larger mass nuclei
• Extremely large amounts of energy released
• More efficient at producing energy than fission

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• Note that the slope of the curve is much steeper
  in the fusion region than the fission region
  (fusion returns much more energy per nucleon than
  fission

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How Does Fusion Work?
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• As you add heat the atoms possess more kinetic
  energy
• The state of matter increases in disorganization

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Plasma

• Fusion reactions occur only at very high temp
  (100 million oC)
• At these temperatures matter exists in a state
  called plasma
• In a plasma, electrons are stripped from their
  nuclei
• A plasma consists of charged particles (ions and
  electrons

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Conditions for Fusion

• Particles must be hot enough (temperature)
• Particles must be in sufficient number (density)
• Particles must be well contained (confinement
  time)

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• In plasma, nuclei are charged repel each other
• The ions must have kinetic energies high enough
  to approach close enough for the attractive
  nuclear force to overcome the electrostatic
  repulsion allowing the nuclei to fuse.

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Selecting a Fusion Process

• Choose a fusion reaction that has a high
  probability of happening and requires the lowest
  temperature

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• The most suitable fusion reaction for the
  production of energy in fusion reactors is
  between the nuclei of the heavy isotopes of
  hydrogen
• Deuterium is plentiful in ordinary water
• Tritium can be produced from lithium

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• 1/6500 atoms of H in sea water is deuterium
• 1.03 x 1022 D atoms in 1 L of sea water
• 1 km3 has energy potential of 1360 billion
  barrels of crude oil
• Tritium is radioactive
• t1/212.4 yr
• generated from Li via neutron capture

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Confinement of a Plasma

• Ions must be held together long enough for fusion
  to occur
• No material walls can contain a plasma millions
  of degrees hot. Either the plasma will damage
  the walls or the walls will cool the plasma

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Methods of Confinement

• Gravity
• Magnetic
• strong magnetic field restricts the motion of the
  ions to a limited space keeps them from
  striking the walls of the container
• Inertial
• an intense energy beam, such as a laser is used
  to heat an compress the hydrogen so quickly that
  fusion occurs before the atoms can fly apart

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Fusion in a Tokamak

• Red toroidal field coils produce cylindrical
  magnetic field
• Blue coils used for special shaping of plasma
• Gray vessel contains plasma
• plasma is very hot (white) at center cooler
  (red) towards outside

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Advantages of Fusion

• Produces large amounts of energy
• Fuels are plentiful
• Inherently safe since any malfunction results in
  a shutdown of the fusion reaction
• No atmospheric pollution leading to acid rain or
  greenhouse effect
• No long-term storage of radioactive waste needed

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Fusion Energy Production

• Enough fuel for the lifetime electricity needs of
  an average person in an industrialized country
  can be produced from
• 10 grams of deuterium extracted from 500 liters
  of water
• 15 grams tritium produced from 30 g of lithium
• if all of the worlds electricity were provided
  by fusion, lithium reserves would last for at
  least 1000 yrs

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Fusion Energy Production

• The fusion energy released from a 1 gram mixture
  of D and T generates about the same amount of
  energy as 2400 gallons of oil

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