Theory
Scattering
Atoms
αβγ decay
Decay Series
Law
Half-life
Geiger
Carbon-14
Fission
Chain Reaction
Nuclear Energy
Nuclear reactors
Fusion

Fusion is where two light nuclei collide and coallesce, releasing energy.

The JET machine is called a Tokamak

Fusion happens successfully in the sun all the time.

Deuterium is an isotope of Hydrogen and is abundant since water is cheap and plentiful in oceans.

Fusion research makes extensive use of magnetic fields to contain the ingredients of fusion.

The sun is our major source of energy and fusion supplies this energy.

Try confining jelly with rubber bands to see the difficulty posed by fusion.

Fusion

Harnessing nuclear fusion has been one of the dreams of the
nuclear age. The attraction of fusion stems from two facts:


1. it relies on fuel that is cheap and abundant and
2. it produces virtually no radioactive waste.

What is Fusion?
Fusion is where two light atomic nuclei combine to form a heavier nucleus with the release of a large amount of energy.
An example is set out below:

When the two particles fuse together their combined mass is less than the sum of separate masses originally. The mass defect is converted to energy – so of it binding energy, the rest released in the reaction.

In order that the two positively charged atoms fuse together, they must approach each other at very high speeds in order to overcome the coulomb repulsive forces between them. The high speeds could be achieved using particle acceleration, but the electrical energy that the resulted energy would yield.

Alternatively, the high speeds could be achieved by heating deuterium gas to extremely high temperatures – 10 to the power of 8k whereupon it becomes fully ionised and is called a plasma. Increasing the plasma’s temperature causes it to expand and so the density of particles falls and so the number of fusions (yielding energy) falls. The difficulty of confining the plasma in a small enough volume at a temperature of 10 to the power of 8k is the major stumbling block at present.

One possibility is to use magnetic fields surrounding a dough-nut shaped vacuum chamber (torus) to control the plasma. The problem of confining the plasma using magnetic field lines has been compared to confining jelly with rubber bands.

Suitable conditions for fusions exist in the interior of stars. The enormous heat output of the sun is thought to be due to the fusion of hydrogen nuclei into helium. So far man’s only real success with worthwhile energy yields from fusion is the hydrogen bomb.


Fusion research


The JET (Joint European Torus) in England has come closest to demonstrating the feasibility of fusion. . It consists of a doughnut-shaped vacuum chamber surrounded by magnets.
The aim is to heat hydrogen atoms to temperatures up to 10 times higher than the centre of the sun, which causes them to break apart and become a “plasma” ---a form of matter approached only by lightning under normal circumstances on earth. Within this plasma, atomic nuclei re-form to produce helium and in the process release a great deal of energy.

What are the difficulties with fusion?

The great challenge of these experiments is confinement. Confining plasma with lines of magnetic force has been compared to trying to confine jelly with rubber bands. As the temperature increases, impurities from the vessel wall enter the plasma, causing problems.