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The Discovery of Fusion Energy

How light elements fuse to make heavier ones and release energy


The world has spent over £100Bn on Fusion research and it is now approaching a final international demonstration of a
Magnetic Fusion reactor, ITER, in France. The project is complex and made more difficult by the need to contract with all the main contributing countries and offer smaller pieces of work to well qualified research groups anywhere. It will be a masterpiece of project management when complete.
All the working components and devices offer the ability to build
Small Reactors with more diverse applications in the immediate future. Fusion will be commercial well before ITER meets its goals.

Laser Fusion is not far behind, but has its own array of technologies yet to be industrialised.

Magnetic and Laser fusion cores can be used to drive an outer blanket running a Fission reactor. The
Hybrid combinations have been widely studied and now represent a key long term goal for both Russia and China.
A Laser version of the
LIFE reactors drives a Molten Salt Thorium reactor and is the most complete design study of any MSThR reactor.
The full scope of our nuclear offerings can be seen on the Fusion picLinks page.

It is always fascinating for any technology to look at it's history when nothing at all was known about it. Our Fusion history is given below.

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Rutherford in Manchester Lab.
1. Rutherford Lab.
Mark Oliphant
Mark Oliphant found Fusion of Hydrogen Isotopes.
2. Mark Oliphant, 1932
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Oliphant's experiment.
3. Oliphant's accelerator Lab
James Chadwick
James Chadwick's model of Carbon with its neutrons.
4. James Chadwick
Invisible particles hit Paraffin
Chadwick's Carbon atom with neutrons changed history.
5. Chadwick's neutron gap
D-T fusion reaction
D-T Fusion: 2+3=4+1, not 5!
6. D-T Fusion cartoon
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D-T Fusion: 2+3=4+1, not 5!
7. D-T Fusion Temperatures
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Nuclear Daisy

It is the energy source which powers the stars.

Let us show how little was known, how it was found and by whom. The people can be as fascinating as their discoveries.

The first major discovery was made by the great German chemist, Bunsen, who saw the spectral lines of Sodium light as he had observed from salt dropped into his flame. At least the sun seems to be made of some of the same elements as make p the earth, but revealed nothing about the source of the sun's colossal energy output.

This primer introduces you to the meaning of the words to describe Fusion and Nuclear energy: The 4 basic concepts of the nucleus, protons, neutrons, and electrons. The 3 basic forms of nuclear radiation. Every strange thing discovered and every device invented has led to thousands of common applications today.

1. The Nucleus

The story of Fusion starts with the discovery of the nucleus by Rutherford in 1911. The Nobel prize winning New Zealander had already found that radioactivity, the spontaneous emission of radiations from some substances, caused a transmutation of the decaying elements into lower elements in the periodic table. Transformations of chemical compounds were well understood, but the collapse of an element had not been seen before.

Uranium decay emits high energy Helium nuclei, which he called alpha particles.

His lab at Manchester University, as shown, was from the days of string and sealing wax, glass tubes and trailing wires, and no Health & Safety. It takes a cunning mind to ask the right questions and devise a way to answer them.

The most basic question was, 'What happens if you run this radiation back into something else?' It is what they did.

He selected a beam of alpha particles from Uranium and ran them into a thin gold foil where they scattered and their scattering angles were measured. Surprisingly, many were scattered to wide angles, just like colliding billiard balls. This meant that gold has a very hard and tiny core to each atom. Thus, the nucleus was discovered - and has produced global industries.

2. Fusion of Light Elements

Hydrogen is the commonest element in the universe and its nucleus is just one positively charged particle, which Rutherford called the Proton, or primordial particle. The Hydrogen atom also has an orbiting electron which makes the atom huge compared with its nucleus. The electron is easily knocked off and Hydrogen ionised. An electric field accelerates the particles in opposite directions, and they can be extracted as particle beams. A cathode ray TV tube uses a fine electron beam to draw a picture. The Large Hadron Collider which discovered the Higgs Boson uses proton beams.

The element Hydrogen is referred to as H and its nucleus as p.

Rutherford moved to Cambridge and created the world's leading nuclear physics laboratory,at the Cavendish.

3. Heavy Hydrogen

Most of his Manchester team came with him, including an Australian, Mark Oliphant. In 1932 he discovered the existence of two heavy Hydrogens, Deuterium and Tritium which were twice and three times as heavy. He also discovered a light Helium at ¾ the weight of ordinary Helium. The 2nd picture is his Cambridge lab. He worked on high voltage accelerators for ions.

4. The Neutron

At the same time, an other brilliant team member, James Chadwick, discovered the Neutron, an uncharged particle - hence difficult to spot - which promptly explained all the weight variations of these elements. Click to see Chadwick's simple, cunning apparatus.

5. The Chadwick Experiment
A Polonium source emits lots of Alpha particles which are absorbed by a sheet of Beryllium, element 4, but something otherwise undetectable crossed the gap to a sheet of paraffin wax, knocking forward a spray of protons which were easily detected. He had found the track of the Neutron! His new model of the Carbon-6 nucleus solved the problem of what the Hydrogen isotopes of Hydrogen, and all the other elements were made of. Nobel prize indeed.

The neutron is called n for short in nuclear equations. These different types are called Isotopes, so Hydrogen has 3, each with its own name and referred to as H-1, D-2 and T-3. Helium has 2 isotopes, He-3 and He-4.

6. Fusion

Now for the exciting energy bit: Oliphant used his accelerator to fire a beam of D-2 nuclei at a target full of D-2. He saw protons and He-3 being emitted. He had discovered the fusion of light elements and the true source of sunlight from the stars. All with string and sealing wax and stuff. This reaction had only happened on planet earth in lightning bolts. Oliphant had found controlled, repeatable fusion in his lab.

How exciting: Uranium can collapse into lighter elements and the lightest elements can fuse into heavier ones. The way the universe is built was becoming clearer.

We must now introduce some sentences which look like equations (horror) but are just easier to write with symbols for the components… the equations or recipes for cooking up the elements? Here are the reactions he had seen:

D-2 + D-2 = He-3 + n + a lot of energy
D-2 + D-2 = T-3 + p + a lot of energy

Another reaction found was between D and He-3:

D-2 + He-3 = He-4 + p + a lot of energy

A basic rule of nuclear reactions is evident here: The total number of nucleons - protons and neutrons - is preserved. 2+2 = 3 +1, 2+3= 4 +1. There is no stable nucleus with 5 nucleons. Instead, the set of 5 nucleons has been split into a more stable pair. The He-4 is the most stable and tightly bound of all because nucleons like to pair up.

Nuclear Stability

This is a very general rule: there is no more than one stable nucleus with any odd number of nucleons. The other variations decay, at various rates towards the stable version. There is no stable nucleus at all with 5, 99, or 193 nucleons. Other elements have up to 9 stable isotopes and 30 unstable ones.

There are no completely stable nuclei beyond Bismuth, element 83. This includes all the heavy fission fuels from Thorium upwards.

The stability of Helium is also why Uranium decay spits out He-4, and other things too.

6. D-T Fusion

The most favourable fusion reaction is D+T:
D-2 + T-3 = He-4 + n + 17.6 million electron volts.

This is shown in the cartoon here.

The D-T reaction happens at lower energy than the He-3 reaction. One tonne of D+T fuel has the energy equivalent of 1.7 million tonnes of coal. The sun does not run on wood chips!

The Neutron is Unstable!

A final remark about the hot fusion neutron: It is unstable outside a nucleus and desperate to be absorbed by something!

A free neutron disintegrates in 15 min into a proton and and an electron, preserving the net neutron charge of zero.

The neutron, the proton and the electron are all spinning, with a spin of ½. Another particle with spin of -½ is needed to conserve angular momentum and make sure the whole universe does not spin ever faster. It is the neutrino, with zero charge almost no mass and is almost undetectable. It interacts so weakly with matter that it can pass through the whole earth without stopping. It plays no part in Fusion energy, except to ensure compliance with the laws of mechanics.

7. Fusion Burn

The ideal D-T burn energy is about 10 thousand volts (10 keV) a temperature of 100 million degrees Kelvin. The temperature in degrees sounds pretty awesome, but in the proper units of electron volts for particle energies, it is quite modest. Electricity grids run at up to 400 kEV, though that voltage only pushes electrons along. The burn rate for hot, light isotopes is shown here using both energy scales.
Regrettably there is little He-3 found in nature as it is really the decay product of Tritium which has to be manufactured in nuclear reactors. Star travel will therefore need D-D Fusion.

PLASMA: The fourth state of matter.

Of course the Hydrogen atoms are stripped of their electrons into a very hot, electrically neutral plasma (the Greek word for stuff) of H's and e's. All elements have some or all of their outer electrons stripped away above 100eV or 1 million degrees, but this is well short of producing significant fusion.

So, the ancients only captured a fragment of the truth about Earth, Water, Air and Fire. These are not elements or elemental, just the four states of matter, Solid, Liquid, Gas, and Plasma. Unfortunately Isaac Newton was taught and believed this at Cambridge and wasted much of his life on Alchemy.

Earthly Fusion: Innovation by the Carbonistas.

Carbonistas? The carbon based life forms known as humans.

The next challenge was to devise a machine which will heat, hold and burn such a D+T plasma.

Hints on how to do this are given in our primers on Magnetic and Laser Fusion. Other options are introduced in Small Fusion and a hint of how Fusion can also operate a Fission system as a Hybrid. The picLinks on the right will take you to these Primers.
The machines are expensive. The economics of Small Fusion is now affordable, as discussed in Economics/Innovation.

Our Nuclear Daisy

The daisy has a Deuterium stalk, with one red proton and one green neutron. It is attached to a Tritium blossom, with one red proton and two neutrons. This represents the Fusion D-T reaction, 2+3 =>5 => 4 +1 . The numbers are shown in the 'grass'. 235 also happen to be the mass of the fissile Uranium fuel, U-235. Just numerology here, but fusion and fission are entangled.
FDS Power Plant
Star Fusion Power
500MW Fusion Core
Hybrid Fusion-Fission
RAL Hiper laser
Laser Fusion: RAL
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Magnetic Fusion
Start Plasma surface glow
Small Fusion
Bodleian library
Fusion Library