Power of the Sun

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

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

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

How Does Fusion Work?

As you add heat the atoms possess more kinetic energy The state of matter increases in disorganization

Plasma Fusion reactions occur only at very high temp (100 million o C) 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

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

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.

Choose a fusion reaction that has a high probability of happening and requires the lowest temperature Selecting a Fusion Process

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

1/6500 atoms of H in sea water is deuterium –1.03 x D atoms in 1 L of sea water –1 km 3 has energy potential of 1360 billion barrels of crude oil Tritium is radioactive –t1/2=12.4 yr –generated from Li via neutron capture

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

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

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

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

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 world’s electricity were provided by fusion, lithium reserves would last for at least 1000 yrs

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