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Nuclear Fusion | |
Acknowledgement
With this final paper, I want to give the reader a clear view on nuclear fusion. I especially want to express my thanks to Mr. Schalley for his great help and support, and for the information he gave me. I also would like to thank the authors of the magazines I used for the photos and the information.
Marko van Dooren
CONTENTS
2 General introduction in the principle of nuclear fusion
3.1 History of research on cold fusion
6 The environmental aspect of nuclear fusion
| 1 | Introduction |
One of the things that makes a difference between a human and an animal is that a human can labor without using his own energy. In the early ages of mankind, people used tools to multiply the amount of energy that they could use. When people became sedentary, they started breeding animals and soon discovered that they could make them do the labour for them. Tilling the land suddenly became much easier because one cow or horse could do the work of several men. The main consequence was that productivity got a boost. Another way of increasing productivity that developed from this idea was slavery by which muscle power was the only source of energy. This situation didn’t changes until the middle ages. In this period the mills were invented, they could turn wind and the streaming of the water into free energy. Again productivity was raised, but still there was a need for muscle power from animals and people. It was with the invention the steam-engine of James Watt that labouring took a complete different turn. The steam-engine could replace dozens of man, and was cheaper. A that time, productivity rose in a way that was never seen before. The work of a thousand men could now be done by a single machine which had only to be supplied with raw materials to provide the user of energy. In this century, other energy sources like solar power and tidal power showed up. People also discovered that oil and gas also could be used instead of the dirty coal. The most powerful energy source, however, was nuclear fission which turned uranium into energy and radio-active waste. Because of the danger of the radiation nobody wants to live near such a power plant. Together with the fact that uranium is rather rare, this makes the alternative form use nuclear energy very interesting. This form is nuclear fusion, by which water can serve as fuel, and the production of energy is higher. Especially the fact the water can be used for a fusion reactor is very interesting knowing that the amount of raw materials is decreasing at fast pace. The meaning of this final paper is to give you a better view on nuclear fusion. In the first chapter, we take a look at the principle of nuclear fusion. In the second chapter we’ll try to explain the history, and the scientific background of thermonuclear fusion. The third chapter will deal with alternative forms of hot fusion. The fourth chapter is dedicated to the state-of-the-art form of nuclear fusion: cold fusion. The environmental aspect is discussed in the Fifth chapter.
| 2 | General introduction in the principle of nuclear fusion. |
We can clearly see that the binding energy per nucleon increases a lot in the beginning of the graph. If you take two atoms with a low atomic number, and would bring them together, you would get an element of which the atomic number is twice a high as the atomic number of the initial atom, because the amount of protons has doubled. Since we have taken elements with a low atomic number, and thus a low mass number, the binding energy per nucleon in the produced atom has increased. Knowing that the binding energy per nucleon is just a unit of the mass defect of the nuclei, we can conclude that the mass defect has increased. This means that mass has "disappeared" and energy is released according to Einstein’s formula. The presence of the speed of light, known to be 299792 km/s, in this formula makes it possible to produce more than a million times more energy than a chemical explosion by transforming one proton or neutron into energy. This opened the way for the most powerful creation since the beginning of times : the H-bomb. Getting this energy out was not really a problem, but getting control of the reaction and actually producing more energy than is put in is another story. The main problem are the coulomb forces (the forces that are caused by the electrical charge of a particle) between nuclei that stop them from melting together to a bigger nucleus. Stars are already doing this from the beginning of times, but mankind just can’t get a grip on it. In the next three chapters, we’ll try to learn something about the three possible ways of beating those Coulomb forces : hot fusion, tepid fusion and cold fusion.
| 3 | Hot Fusion |
3.1.1 Trial and Error from 1938 to 1956
A. Research
An interesting thing about the research of nuclear energy is that the principle of both nuclear fission and fusion were discovered at the same time, back in 1938. Nevertheless, nuclear fission research already led to the construction of a reactor in 1942, whereas nuclear fusion stayed far behind. The consequence of the progress of nuclear fission was that most people had forgotten the existence of nuclear fusion. Only in the late forties, the idea of fusion began to attract widespread attention. At that time, the Argentine dictator Juan Peron had set up an island laboratory for Ronald Richter, a German Scientist who had explained him the idea of nuclear fusion. In march 1951 the report on the results of Richter’s experiments hit the headlines. Peron proclaimed the Argentina had surveyed the efforts that scientists in other countries were making to design uranium fission reactors and had elected the risk of taking the direction of designing fusion reactors.
On February 16, 1951, Richter had done experiments that should be a great progression according to Peron, and so he published a report in the newspapers. The lack of details, however, moved other prominent scientists in Europe and America to express their scepticism in the newspapers.
Although this experiment turned out to be a canard, nuclear fusion was not put away. Gradually, scientists began to acknowledge the existence of nuclear fusion, though it seemed impossible with the knowledge of the laws of nature at that time. This however, meant an enormous challenge for the curious scientists, and because they were allowed to pursue their own activities, in these days, the report even started a wave of scientific research.
A crucial element is the early years was the possible use of fusion in weapons. The government saw it as a potential instrument for making heavy nuclear bombs. A consequence of this was that nuclear fusion became an issue of national interest, and with the cold war dominating in this period, the research and experiments became a state secret. An interesting aspect, however, is that nobody had the purpose of using nuclear fusion for future energy supply.
Another interesting thing about fusion research is, that scientists thought it would take only a few years to solve all the current problems. This was a consequence of the general atmosphere of optimism after the war. Scientists thought that everything was possible. Thomas Johnson, director of the Research Division at Princeton, estimated that it would take only 4 years and one million dollars to find out whether it was possible to contain a hot plasma. The general opinion was that the construction of the first operational reactor was only 10-15 years away. Today, scientists know for sure that it will still take decades to find out if it is possible to build one. However, not everybody was so optimistic about the progress in fusion research. Spitzer, one of the scientists researching nuclear fusion, and his associates said that the optimism should depend on the technological progress. Either the plasma would be quiescent, or it would be turbulent. In the latter case, many fusion programmes would be dropped, because it would be almost impossible to get control over the plasma, and it would take a lot of time and money to figure out how to stabilise the plasma.
B. The actors
The main actors in the initial years of fusion research were the United States, the Soviet union and Great Britain. They encouraged and invested in the fusion research. The governments were only passive actors. The research was so autonomous that, in 1951, Spitzer at Princeton did not know that Teller at Los Alamos had also been conducting fusion research for several years.
Great Britain was the pioneer in fusion research, even before the Peron incident, according to Elaine Potter, a fusion scientist. Their main institute was the Imperial College in London. This was the first place in the world where controlled fusion experiments were conducted. The initiative came from professor G.P. Thomson, a Nobel laureate who had also worked on nuclear bombs and hydrogen bombs in America. Their research led to the construction of an annular magnetic bottle1) to confine to plasma. This is the same principle that is applied today.
Unfortunately for the British, they could not keep their leading position very long. The famous spy Klaus Fuchs, who had also revealed the secret of the A-bomb to the Russians, now passed on the knowledge of the British research to them, and with Igor Tamm and Andrei Sacharov, two scientists who had also worked on the H-bomb, they had the brain-power to compete with Great Britain and the United States. In 1950, Ivor Kurchatovs became interested in fusion, and he set up the Kurchatovs Institute in Moscow, where Lev Artsimovitch could do nuclear fusion research with a team of more than 100 other scientists. A few years later, it was this team that succeeded in constructing the Tokamak, which simply means a power machine. This device is still used in present fusion research.
The Americans started their fusion research at about the same time as the Russians. Initially, it was "a kind of hobby of the A-bomb scientist James Tuck"2) , but soon other persons and institutes also started their fusion experiments. In these years the funds for the research increased every year. The following table shows the research costs at Los Alamos, Livermore, Oak Ridge, Princeton and Washington. The amounts do not include the construction and equipment funds.
| Fiscal Year | Total Operating costs |
| 1951-53 1954 1955 1956 1957 |
1.74 million dollars
10.74 million dollars |
Source: Bromberg (1982:44).
The American funding was certainly influenced by Peron’s report, which caused a huge research wave. The two main scientists in the first years of American fusion research were Lyman Spitzer at Princeton, and Edward Teller at Los Alamos. The Americans had soon build their device, the Stellarator. The Stellarator survived until 1969, when the Tokamak became the most commonly used machine.
Current fusion scientists see this period as a period of trial and error, in which scientists tried to understand all the problems they met in their research. There wasn’t any form of co-operation in this period, not even between the U.S.A and Great Britain, as this was forbidden in 1951. Fusion research became top-secret, because of the cold war, an arms race and a war in Korea.
3.1.2 The road to the Tokamak: 1956 - 1968
Politics played a major role in these initial years. This is the reason why 1956 is seen as a milestone in the fusion research. It was then, that a Russian delegation of scientists came to Great Britain, to give a speech in the Harwell Laboratory. With Stalin ruling this had been impossible during the first period of research, but Ivor Kurchatov convinced the new Soviet leaders of the positive effects of such a lecture. Potter pointed out three reasons for this development. First of all, the relations between the U.S.A and the Soviet Union got better with Stalin’s death, and the coming of Eisenhower, who called for international cooperation. Another reason is the disappearance of the optimism. Scientists no longer thought it was a possible to produce heavy nuclear weapons on short term, and so it was better to cooperate. The last reason was that many scientists were concerned about the future of nuclear fusion. If they didn’t start working together, the government would probably invest less money in fusion research, because there was no advance.
In this period, it was the first time that another use of fusion power was mentioned. Jim Woolridge said that fusion power could provide people with endless amounts of power, and it would produce less radio-active waste than nuclear fission.
The third international conference on plasma physics and thermonuclear fusion in 1968 was the final breakthrough for the Tokamak device. The results in temperature, density and confinement were much better than all the other results. This was the reason why the other countries dropped their own devices, and started to build Tokamak devices. Only the U.S.A did not do this as a result of the costs of the Vietnam war, which reduced the funds for fusion research by 2.5 million dollars.
3.1.3 Research from 1968 - 1988
The aspect of energy production made nuclear fusion known all over the world in only a short time. Fusion could provide mankind with endless amounts of energy and it was better for the environment because there was no danger of a melt-down. Besides, the only radio-active waste that was produced was tritium, and with its half-life of 12 years, it wouldn’t take long before the radiation would be gone. Another advantage of fusion was the production of helium gas as a spin off, which is very valuable.Especially the fact that it wasn’t very harmful to the environment made the funds go up dramatically. It was at the beginning of this period that governments started spending enormous amounts of money at research for clean energy sources. Of course, fusion research became the favourite project to use that money on. With these new funds a new wave of optimism was felt. Robert Hirsch, the director of the American Atomic Energy Commission, expected that scientific feasibility would be proven around 1981 and he predicted the building of a reactor in the mid-90s.
With these rising funds, scientists could drop the tradition of basic research in fusion. They now could start designing functional reactors in order to get some evidence of the feasibility of nuclear fusion. In 1976 there were plans for a new programme for fusion research. It took two years before the programme took off. On June 1, 1978, the European Community started the JET programme (Joint European Torus). JET was a 12-year programme for building a large Tokamak device for research. The initial members were Euratom, the members of the EU and Sweden. Later, Switzerland also joined the group. The members were not allowed to leave the project within the first five years.
The choice of the location is a fine example of how the governments got more and more involved in the fusion research. There were four possibilities: Germany, Great Britain, France and Italy. The best places to build the JET were Harwell in England, and Garching in Germany. The reason why the JET ended up in Harwell, England was a hijacked German aeroplane. In the autumn of 1977, an aeroplane from Lufthansa was attacked by a group of terrorists. Then the German Chancellor Helmut Schmidt was offered the help of the British anti-terrorist group SAS, by the British Prime Minister. The SAS would rescue the passengers, and Germany would get all the credit. When the SAS successfully completed the mission, Helmut Schmidt was honoured for it. In return for this, Jim Callaghan, the British Prime Minister, said that he wanted JET, and so the JET got the British identity.
One of the reasons why JET was started was the fact that America had built the Princeton Large Torus and Japan was building a Tokamak. This means that Europe had to come up with its own research institute soon in order not to stay behind in nuclear fusion. Another reason was the oil crisis. Western Europe produced 60% of its energy with oil, and almost all of this oil was imported from the Middle East and North Africa. This meant that Europe had become very dependent of the Middle East and North Africa, and so the EU had to find a way out of this uncomfortable position, this way was nuclear fusion. Not only Europe had become vulnerable, but also the United Stated used oil for 46% of their energy, of which one third was imported, and Japan needed foreign oil for 73% of its energy. This mighty position of the Middle East and North Africa must have been seen as a great threat, because in this period, the International Energy Agency was established to work on this problem.
On may 25, 1982, the EU Council of Ministers made a decision that ensured the continuation of JET until 1986. It was in this period that the scientists and politicians strove after an even higher level of cooperation, and thus started to work on plans for ITER.
The JET (above : the outside, underneath : the inside)
3.2 Contemporary fusion research : ITER
The ITER programme, the successor of the JET, took off on February 26, 1988, and was launched by Ronald Reagan and Gorbatchov. ITER is the abbreviation of International Thermonuclear Experimental Reactor. The ‘I’ that stands for International indicates the growing cooperation. The participants are the EU, Sweden, Finland, Austria, the USA, Japan and the Russian Federation. ITER was supervised by the International Atomic Energy Agency. This internationalization of fusion research was caused by the growing doubts about fusion research and the increasing pressure on the budgets. The pressure came especially from the tax payers. They wanted to know what happened with their money since there were no results.
3.2.2 The structure of the ITER
Since all the participants wanted to take a certain part of the project into account, the structure of the ITER soon became pretty complex and would seem a lot of nonsense in the eyes of the public. Also many scientists disliked the structure because science shouldn’t have anything to do with politics, and instead of the integration of the best scientists and the best installations, the politicians made it a too ambitious programme to shows how good the political cooperation could be, and integration became impossible. The norm of this political interference was the firing of the former director, Mr. Rebut because he didn’t care about politics. Let’s take a look at the structure of the ITER.
The internal Reactor components would be made in Garching, Germany. The external reactor components were for the account of Naka, Japan. All these components would be brought together in San Diego, USA, to form a single unit. The director of the programme would be a European whose office would be located in San Diego. He and his staff are subject to the control unit called the ITER Council, which would be Russian and located in Moscow. In addition to these units there would be two committees: the International Technical Advisory Committee whose leaders come from the USA, and the Management Advisory Committee, headed by Japan. Alongside this general structure of the ITER, there were also smaller projects in some Western countries. These projects are all somehow integrated in the ITER programme. The following table shows us the research institutes in Europe.
| Countries | Plasma confinement and heating | Technology |
| Belgium Denmark France Germany Italy Netherlands Sweden Switzerland United Kingdom |
Brussels Risö Fontenay and Cadarache Garching and Jülich Frascati and Padua Nieuwegein Stockholm Lausanne Culham |
Mol Risö Saclay Berlin Frascati and Casaccia Petten Studsvik Villigen Harwell and Springfield |
| European Union | Culham (JET) | Ispra and Petten (GCO) |
The fact that the projects are smaller, however, doesn’t mean that they are less important. For instance, take the research programme in the Netherlands: the FOM (de Stichting Fundamenteel Onderzoek der Materie). FOM is a subunit of the NWO, the Dutch organization of scientific research. It was this institute that discovered that a plasma does not behave like a homogenous gas, but like a tangle of spaghetti. This means that the size of the reactors can be reduced and so the amount of energy required to get the fusion going decreases. According to Mr. van der Wiel, the director of the FOM, this discovery was the absolute hit at the fusion conference in Lisbon in 1993.
The general task of the ITER is to build a reactor in order to study plasma confinement under thermonuclear conditions. The experience and the results of the JET should be the base of this reactor because the JET is the most advanced device to this moment and has given the best results. The conditions in the JET have reached 80% of the break-even, which is hoped to be met with the ITER. After the ITER, it is time for the Next European Torus (NET). The goal of this operation is to build an experimental reactor. In the programme from 1994-1998 the main objective is to make the engineering design of the NET, the International Thermonuclear Experimental Reactor-Engineering Design Activities (ITER-EDA). This project is carried out by the ‘Joint Central Team’, the four ‘home teams’ and in the specialized institutes in the different countries. In addition to these ‘next step’ activities, two other researches are being carried out between 1994 and 1998. The first one is the research on improvements in the plasma physics and technology, the other research is dedicated to long-term technology. This period from March 21, 1994 - July 1998 is called the Protocol 2-ITER-EDA. Protocol 2-ITER-EDA would mean the end of JET, but some people believe that the JET can still be useful after its decommission in 1996.
The objectives of the ITER are the following:
The scientific feasibility refers to a break-even while engineering feasibility refers to high-energy gain. These are the two aspects of the technological feasibility. The break-even has always been promised to be reached within a few years, and now this has to be done once more. The promises keep the scientist and the sponsors going on. Very small steps of progress are said to be very important, and the break-even is called the break-through for nuclear fusion. Once they are thus far, the commercial feasibility must be demonstrated. This means that fusion should be a "socially and environmentally acceptable energy source that is economically attractive compared to its alternatives"3) . Walter Marschall, one of the most prominent scientist and managers in the field of both fission and fusion says in an interview with the BBC on April 8, 1994, that he believes that fusion will never be commercially feasible because it would simply cost too much money.
The existence of life is a consequence of two fusion reactions. The first one is called the proton-proton chain, the other one is the carbon-nitrogen chain.
1 The proton-proton chain
The proton-proton chain starts with the fusion of two protons, which results in the production of a deuterium nucleus and the emission of a positron (a particle with a positive charge, but no mass) because one proton is transformed into a neutron and so it has lost its charge.
Now the deuterium nucleus melts together with a proton to form a helium nucleus.
The gamma ray (g ) is a ray of energy, and is the most dangerous form of radio-active radiation. When both of these reactions have occurred twice, the two helium nuclei will interact with each other.
Because of the terrible heat, the atoms were separated in nuclei and electrons. The two positrons formed in this reaction will be annihilated together with two electrons when they collide with each other. This reaction will also produce energy.
This annihilation releases another 1,02 Mev per positron. If we add up all the energy that is released, we can conclude that this reaction produces 26,7 Mev (2 * 0,42 + 2 * 5,49 + 12,86 + 2 * 1,02).
The result of this reaction is the transformation of four protons into one alpha-particle and 26,7 Mev.
2 The carbon-nitrogen chain
The carbon nucleus absorbs the protons and is transformed into nitrogen, carbon and oxygen. At last another carbon nucleus appears together with a helium nucleus.
We can see that the carbon nucleus that is used in the first reaction reappears after the last reaction. This nucleus has served as a catalyst. The total energy released by the fusion of four protons (including the annihilation of the two positrons) is also 26,7 Mev.
The energy released per mass unit (protons in this case) is 6,67 Mev (26,7 / 4). If we compare this to the energy per mass unit in a fission reaction with a 235U atom (200,5 Mev / 235 = 0,85 Mev per mass unit) we can see that the energy per mass unit by a fusion reaction is eight times a high as that from a fission reaction. As a matter of fact, this means that one kilo of hydrogen can release eight times more energy than one kilo of uranium. The advantage is that there is an almost inexhaustible amount of hydrogen on earth is almost inexhaustible and it costs nothing while uranium is rather rare and very expensive.
Both of the reactions happen in all stars. The p-p chain is dominant by small stars, while the C-N chain is dominant by larger stars because the C-N chain demands a higher temperature. These fusion processes keep the star from collapsing by gravitation. Once all the hydrogen is used, the gravitation wins from the fusion power and the star gets smaller, but meanwhile the temperature increases dramatically and so the helium nuclei can melt together to beryllium. Once this helium is also burned up, the gravitation crushes the star. But if the star is large enough, it will continue creating heavier elements out of lighter elements. If beryllium is combined with helium, it forms carbon, and this keeps happening while the star keeps heating up. When all the nuclear fuel is gone, the star dies. But doesn’t fusion only happen if the binding energy of the product has increased relative to the binding energy of the used nuclei? Yes, that’s true, and if we look at the curve of the binding energy again, we can see that it starts to decrease at the middle of the graph (from the element Fe), so what about the elements with a larger mass number than Fe? If a large star has used all its fuel to create heavier elements, and finally has produced iron (Fe), all the power to resist the gravitation disappears. At that moment, the star is crushed at a tremendous speed causing it to heat up to a few billions of degrees. Then the iron centre of the star collapses and the jacket of the star is launched away by the most powerful explosion in the universe: the supernova.
It is during this supernova that elements heavier than iron are born. The enormous pressure and temperature makes it possible for these heavier atoms to be created. And so all the elements known to mankind are made by two things: nuclear fusion and hydrogen.
It is clear that the fusion reactions mentioned above are impossible to conduct on earth because the required temperature is much too high (1,5 * 109 Kelvin). People already used fusion in H-bombs and atomic bombs, but the energy that is released isn’t useful. But we want to have a fusion process that doesn’t demand such a high temperature and that can be controlled in order to produce energy. The first problem was quickly solved. Scientists found the next reaction which is the best for the practical use.
The deuterium (d) can be found in nature, but the tritium (t) must be made by the scientists. This reaction requires a temperature of 100.000.000 Kelvin, and so the electrons and the nuclei of the atoms are separated. For the practical use, is easier to conduct fusion at a temperature of 200.000.000 Kelvin.
To find out when we have a permanent fusion process, we insert some parameters: the temperature of the plasma and time that hot plasma in the active volume of plasma needs to join the fusion reaction, also called the confinement time. After that time, the hot plasma leaves the volume and is replaced by new relatively cold plasma. The condition for a constant fusion reaction is that during the time that the plasma is in the volume, it produces enough energy by means of fusion to heat up the new plasma, and to make up for the loss of energy by the radiation of electrons. The most profitable values of the variables with the eye on the practical use are :
| nt = 1020 s/m3
T = 2*108 Kelvin |
These conditions are called the Lawson criterion. These conditions are only valid when we’re talking about hot fusion.
The main problem is to meet all these requirements. In some tests the density of the plasma was high enough, but the confinement time was too low, or the temperature wasn’t high enough to reach the necessary reaction speed.
Let’s take a look at the three devices that are developed for meeting the Lawson criterion.
We’ll first take a look a the most popular way of trying to meet the requirements for nuclear fusion. The device is called Tokamak, and is Russian, but it’s based upon the same principle the Americans used for their Annular Magnetic Bottle. Of course, the development of this enormous machine wasn’t as easy as scientists hoped. They thought they could control nature, but soon learned that is was the other way around.
The two main problems at the beginning stage of development were how to lock in the plasma and how to reach a temperature of 200 million degrees Kelvin. No material can contain plasma without being destroyed, and the plasma loses too much energy when it touches common material. We first need to know the behaviour of a plasma before we can solve this problem.
- Plasma heats up when a current flows through it because of its electrical resistance. But this only happens in the beginning stage since the resistance is reduced dramatically when the plasma reaches a temperature of 107 Kelvin.
- As a consequence of a current flowing through the plasma, a force works perpendicular on the magnetic field caused by the current: the Lorentz force. This force makes the plasma compress, causing additional heat, and is called the "pinch effect". If the compression speed is too high, this results in the release of heat by shock-waves and turbulent processes which must be avoided to be able to control the plasma. The next pictures show a stable plasma (top) and an unstable plasma (bottom).
- Plasma can be heated up by a high-frequency magnetic field.
- Plasma can be heated up with rays of atoms with a very precisely defined energy.
- Plasma can be heated up with high-intensity laser beams.
- Plasma can be heated up with high-intensity rays of electrons.
With the knowledge of these properties of a plasma, American scientists built the Annular Magnetic Bottle, and the Russians constructed their Tokamak device. Both of the machines used the same principle of containing the plasma. The next picture shows the main elements of these devices.
The alternating current in the primary winding (red) makes the iron centre act like a magnet, and thus creates a constantly changing magnetic field. This magnetic field makes a current flow in the gas in the torus, and this way it heats up the plasma. The main purpose of this magnetic field is to heat up the plasma. A side effect of the current in the plasma is the "pinch effect" which helps to stabilize the plasma.
The spools that go round the torus (blue) create a magnetic field in the plasma and so locks in the plasma in order to protect the torus and to prevent loss of energy when plasma touches the torus.
It’s obvious that the latter magnetic field has to be very powerful in order to keep the plasma safely in the right position. In the initial period, scientists got stuck here. In order to realize such a strong magnetic field, the magnets would use more power then could be released with fusion. The solution came with the discovery of super-conductors. These are materials that don’t have any, or a tiny electrical resistance when their temperatures approach 0 Kelvin, and thus don’t use any significant power. This way they can create strong magnetic fields. The problem seemed to be solved, but another problem showed up. A very fine cooling system had to be developed to cool down the spools because within a few meters away from there was a plasma with a temperature of 200 million Kelvin. This cooling system consists of a barrel with cooling fluid that surrounds the torus, and a heat-interchanging system. The fluid heats up in the barrel, and then is pumped to another cavity where it passes on its heat to the water of a steam engine that produces electrical energy.
It was already clear that a reactor would become a very complex thing, IF it would ever be constructed.
Now they locked up the plasma, and heated it up, but it’s still a long way to nuclear fusion. A first reason is that the plasma isn’t hot enough yet for the fusion reaction (10 million degrees Kelvin), and so we have got to add components to heat it up. First, we shoot particles with a high energy into the plasma, and so we heat it up. Another of these components, is a special antenna, developed by a team of the Laboratorium voor Plasmafysica from the Royal Military School in Brussels. This antenna emits microwaves with a frequency of 32,5 MHz, causing the nuclei in the plasma to reverberate, and thus to heat up. Yet another problem showed up: how to supply the antennas of energy to heat up the plasma? The antennas need 2 megawatt. The energy supply for these antennas was quite large and extremely complex. The next picture shows a man installing the antennas (the panels he sits in front of).
Now the heat problem is solved, but we also need to protect the wall of the torus because it can’t stand the heat at such a short distance away from it. Research groups found that a thin layer of titanium-carbon would be the best protector. However, this thin layer was not sufficient because it didn’t hold long enough to protect the wall during the whole fusion reactor, and they had to make up the loss of protector. To do this, two techniques were developed. The first one is to bring vapour of titanium-carbon into the torus by means of electrical discharges. By the second one, the protector is squirted on the wall of the reactor by a strong vacuum. This last technique gives the best results.
The fusion reaction is started and contained when the reaction speed is high enough and the fusion reaction produces enough energy per second to stabilize the temperature. That’s necessary because the plasma emits energy, and that energy must be made up by the energy of the fusion process. The energy of the helium nuclei, about 25% of the total energy release, goes to the plasma because they have an electrical charge and thus are locked in. But the Helium nuclei do not have enough energy to keep the reaction going. The problem here is that the neutrons that possess 75% of the fusion energy, can not be kept in the plasma. The neutrons will escape out of the plasma, and with them 14,08 Mev per neutron.
Of course to let these neutrons just get away with all that energy must be avoided. The neutrons go through the thin wall of the reactor, but in the barrel of the cooling system they collide with the cooling fluid atoms, and they pass on their energy. The energy is thus not completely lost, but still there is a great loss of energy. The escape of neutrons can also be useful, though. We already know that tritium has got to be created by the scientists. If we use Lithium as a cooling fluid, the neutrons split the Lithium in Helium and Tritium.
While circulating, the tritium is separated from the cooling fluid and inserted in the plasma and the problem of having to create tritium is solved.
The technical problems now seem to be solved, but still there is no permanent fusion reaction. There has been fusion for two seconds in the JET, but it took 15 - 20 megawatt of electricity to free 2 megawatt of fusion energy. Also at Princeton, fusion has been achieved once, but the production of 10 megawatt cost 17.000 megawatt. Now scientists are working on the prolongation of the fusion reaction. This should be done by raising the confinement time of one second, and the density which is about 1019 - 1020 particles per m3 at this moment. When they succeed, the efficiency of the Tokamak will rise because the plasma is already heated up. Finally, when the reaction can be continued long enough, that reactor will be able to produce energy instead of costing energy.
3.3.4 Fusion with lasers and particle beams
Fusion with lasers and particle beams is completely different from the Tokamak principle. By this type of fusion, the deuterium and tritium are put into a little pellet of glass. The result is a density between 1030 and 1031 particles per m3. The reaction chamber is round, and it’s the end of many huge guns. These guns shoot laser or particle beams. That depends on the type of reactor. The principle of both reactor types is exactly the same, though.
Since Isaac Newton wondered why apples fell off a tree, the scientific knowledge of mankind is enriched with a few new laws of nature. One of them says that wherever there is a force, there always is a reaction force. It’s that reaction force that is used to conduct the fusion. The next picture shows how that happens.
When the pellet reaches the center of the reaction chamber, the guns fire all their energy (lasers or particles) towards the pellet. This causes a small supernova. The outside of the pellet, the glass, is blown away with a speed of 105 till 106 metres per second, causing an enormous reaction force. In about 10-9 seconds the nucleus of deuterium and tritium has reached a density that is 10.000 times a high as in the beginning as shown in the following pictures. The time after the blast is typed underneath (1 ps = 10-12 s).
| 350 ps | 400 ps | 450 ps | 500 ps | 1000 ps |
Together with the terrible heat that is developed, this causes fusion of the deuterium and tritium. Lithium fluid flows past the wall of the reaction chamber and transmits the heat to a steam generator. The constant injection of pellets should cause the reactor to produce more energy than is put in. This means another a difference with the Tokamak, where we can speak of one constant fusion reaction instead of many fusion reactions per second. To produce 1000 megawatt of energy, the fusion of 10 pellets per second is required. That’s the point scientists are working on these days. We’ll now take a look at two prototypes to get an impression of the size of a possible fusion reactor.
The PBFA-II
PBFA stands for Particle Beam Fusion Accelerator. This device uses particle beams to blast the pellet. The guns are 36 particle accelerators with a length of 30 meters each. The reactor is put into a tank filled with water to reduce sparkling. The PBFA is the most powerful testing installation in the world with its capacity of 1011 megawatt.
The GEKKO XII
This picture of the GEKKO XII in Osaka, Japan, shows the laser guns that intensify the laser. The laser cannons of the NOVA in the Lawrence Livermore National Laboratory in California, USA, have a length of 137 meters each, the reaction chamber has a diameter of 4,6 meters and consists of an aluminum wall with a width of 13 centimeters. The lasers are pointed towards the center of the reaction chamber with mirrors that can be controlled from within a secured computer room. The lasers of the NOVA can fire maximally 20 times a day. Large batteries lay in energy to supply the cannons with, a disadvantage is that it takes a long time for them load up. Both of the installations can produce 10 trillion fusion reactions with one single pellet.
| 4 | Tepid Fusion |
A long time ago, people already knew that deuterium and tritium occasionally combine and form a molecule. The nuclei of both atoms repulse each other because they both have a positive electrical charge.
In 1947, Andrei Sacharov wondered what would happen if the electrons from the molecule are replaced by muons. Muons are particles with the same electrical charge as an electron, but with a mass that is 207 times as high. They can be create by shooting electrons or light atoms towards another material with an energy of 1 Gev. The production of one muon in the current particle accelerators costs between 5 and 10 Gev. Because of their relative heavy mass, these muons can easily replace electrons by just pushing them away. The result of this replacement is that the size of the atoms is reduced with a factor 1/200, and so the coulomb force decrease. Deuterium with a muon instead of an electron is called dm , tritium with a muon is called tm . When a dm atom collapses with tritium, the muon is passed on to the tritium since it combines better with tritium. The decrease of the coulomb forces makes is possible for the deuterium and the tm to form a complex molecule.
The dtm -ion is almost similar to a H2+ -ion, but it’s much smaller since is has a muon instead of an electron. The distance between the deuterium and the tritium in the ion is about 0.5 * 10-12 m. Under these circumstances, fusion reactions can already appear by low temperatures.
The alpha particle and the neutron can be used to produce energy, and the muon can be used again as a catalyst for other fusion reactions. The alpha particle and the muon are released as one single atom and normally will split immediately. Though, there is a very small chance that the muon and the alpha
particle stay together and become useless. Taking that into account we can come to the following scheme, that describes the tepid fusion process.
The only problem is that a muon falls apart 2,2 m s (10-6 s) after it is created. One fusion reaction takes about 0,02 m s by a temperature of 1800 Kelvin. This means that one muon can cause 100 fusion reactions. The temperature of 1800 Kelvin is the reason why this type of fusion is called tepid fusion. In order to get a "break-even" (producing as much energy as you put in), one muon should cause 300-600 fusion reactions. The best result is 150 fusion reactions per muon in the Los Alamos Muon Factory. In commercial reactor there should be about 1500 fusions per muon to make it profitable.
In 1956, Luis Alvarez from the university of California observed tepid fusion in a mixture of deuterium and hydrogen. At first, he was happy, but the lifetime of a muon is not that much longer than the time that is needed for one fusion reaction of deuterium and hydrogen, and so a "break-even" was out of the question.
Twenty years ago, tepid fusion was a strange scientific thing until in 1977 two Russian scientists said that a fusion reaction with deuterium and tritium would be much quicker than one with deuterium and hydrogen, and so the production of energy could be increased. This idea led to the principle mentioned above.
Calculations have indicated that, with a few improvements of the apparatus, the amount of reactions per muon could rise to 300-1000 reactions per muon. In other words: tepid fusion is a very realistic way of nuclear fusion and maybe has a better future than cold fusion and hot fusion although it is less known.
| 5 | Cold Fusion |
5.1 The tragic birth of cold fusion
It was on March 23, 1989, that cold fusion was presented to the world for the first time. Professor Martin Fleischmann and his assistant Stanley Pons from the university of Utah, once his student, declared in a press conference on April 12 that they had obtained nuclear fusion by one of their experiments on March 23. The fantastic aspect of this fusion was that the temperature to start the fusion reaction wasn’t 200 million Kelvin as usual, but just the room-temperature. The media jumped on it right away and soon the important newspapers and television stations came with stories about an endless source of energy that would be for free. Scientists scratched their heads. For decades they had been trying to achieve their dreams with the most advanced techniques. Their reactors got incredibly large, and still they didn’t produce more energy than was put in. And now, two scientists claimed to have solved the problem on a ridiculously simple way, and these two weren’t even physicists, but they were electro chemical researchers.
Almost every country, even Belgium, started research groups and huge amounts of money were put in. The university of Utah set up the National Cold Fusion Institute right away. A 5 million dollar grant was given for their research. These research groups tried to repeat the experiment. In the beginning, the results were positive. Scientists at the Brigham Young university, the A&M university in Mexico, Georgia Technical University as well as researchers in India, the USSR and Hungary confirmed they had observed activity of neutrons, a sign of fusion. At the university of Washington there was no sign of heat or neutrons, but from other side-effects of fusion. Pons said that at a certain moment, 30 institutes confirmed their discovery and there were also positive results in Italy, where fusion reactions had taken place by a temperature of -100 degrees Celsius.
On April 25, the dream of Pons and Fleischmann collapsed. Georgia Technical withdrew its announcements because of the supposition of malfunctioning apparatus or bad experiments. Eventually more evidence about the fact that there hadn’t been fusion showed up. On April 27, the people of the American magazine Nature declared that the report they were sent for publication did not contain any additional information about the experiments, and so their announcement on cold fusion was considered a joke. Pons and Fleischmann were accused of sloppiness and even fraud. The National Cold Fusion Institute in Salt Lake City was closed immediately.
Pons left the university of Utah because of the extremely annoying situation he had gotten into. Fleischmann continued his research in a laboratory in the French Alps about ten miles away from Nice, on funding of Toyota. The Toyota company found cold fusion interesting because they saw it as a possible energy for their cars.
According to Fleischmann, they paid the first five years of their research at Utah University with their own money. He explains this fact with three reasons. The first reason was that they didn’t want to tell anybody. Another reason was that they didn’t want anybody else to interfere with their research, and thirdly because they probably wouldn’t get the money anyway. Because of these reasons they didn’t tell anyone about their research, and so didn’t ask for a grant.
What Fleischmann and Pons didn’t know was that Steven Jones, a famous fusion scientist of the Brigham Young university, was also doing research on cold fusion. Jones had also done very successful research on tepid fusion. When both groups found out about each other doing the same research, Jones wanted to publish his results. This forced Fleischmann and Pons to reveal their activities to the heads of the university of Utah. Immediately patents were applied for, and fundings were required for. The result of this hurry was the dramatic press conference on March 23. The two researchers weren’t prepared well enough yet for a press conference because their research and experiments weren’t completed yet. And so their research was rejected by the media and most of the scientists.
Fortunately, not all the scientist thought the same way about cold fusion, and some of them also started researching on cold fusion. The wave of scientific research, however didn’t have the extent of the Peron accident, but it certainly woke up the interest and dreams of certain scientists. This led to a conference on cold fusion at Lake Como in Italy, in June 1991. Cold fusion was still alive.
The general idea on cold fusion is getting more widespread. In June 1990, Fleischmann published another paper on cold fusion, and the only reaction given was a positive one by a European scientist who had formerly criticised their research, but now withdrew his criticism.
Storms, another scientist researching on cold fusion, says that there is real progress. In a review in the Journal of Fusion Technology, he says that from the 40 experiments in a survey, 21 of the testing installations produced more heat than they were supplied with, in 13 experiments the production of tritium was reported and in 36 experiments, neutrons were detected. These experiments give us the evidence that cold fusion does exist. The questions are when scientists understand exactly what happens and how they can use it.
Only one man actually checked the data that were put on paper by researchers from MIT who had investigated Fleischmann’s experiment for the Federal Government. It was Eugene Mallove, the former chief science writer for MIT news service. He saw that the results on the heat release that had been published showed no excess heat, while the results of the detectors do show excess heat. He says that the data had been manipulated in order to reject the idea of cold fusion. So instead of investigating this new form of energy, they tried to make it disappear according to Mallove. Mallove says the reason they did this was the fact that hot fusion probably would be replaced by cold fusion because cold fusion research was be much cheaper, and the results were much better. This means that the MIT, a research centre for plasma fusion, would lose its 20 million dollar fundings. To prevent this, they deliberately tried to make people believe that cold fusion was nonsense according to Mallove.
5.2 The experiment of Fleischmann and Pons
Actually, the experiment had already been conducted in 1926 by the German chemists Fritz Paneth and Kurt Peters, and although fusion wasn’t known yet, they predicted that the sun produced its energy the same way. A year later, they announced in an article in the magazine Nature that the helium they had detected had entered through the thin glass of their apparatus. Meanwhile, somebody else started thinking. In 1927, John Tandberg, who had had success with a similar experiment, asked for a patent for "producing helium and energy" in Stockholm, but he didn’t get one. Since that moment, interest in cold fusion dropped until March 23, 1989.
The reconstruction of the famous experiment is very simple, only the explanation is so difficult that nobody has figured it out completely yet. The formation consisted of one glass with a mixture of LiOD and heavy water (D2O),( Paneth and Peter used normal water), an electrode of palladium and one of platina and an accumulator for the energy supply. When Pons and Fleischmann started the electrolysis, they detected excess heat, but no radiation. Several scientists believe to have found the explanation for this.
A former student of Fleischmann found that if he forced the palladium full of deuterium, he always got excess heat. So he claimed to have proved that there is heat production. In one of his experiments, he placed a spent electrode from a fusion cell on a film, and put the formation in a dark room. When he looked at this film 12 days later, he saw a pattern of bright illumination on the film. The pattern could only have been caused by radiation. Since there was no light in the room, the pattern must have been created by nuclear radiation from the palladium. So he says to have proved that cold fusion indeed is a nuclear process as some scientists ignore.
Dr. Randell Mills of the Hydrocatalysis Power Corporation claims that the interpretation of cold fusion and 70 years of nuclear physics are wrong. His calculations predict a new form of hydrogen which was never known before. He thinks that the electron can jump to an orbit with a distance to the nucleus that is much shorter than usual, and that this process releases heat. His experiment was similar to the experiment of Pons and Fleischmann, but he used normal water and an electrode of nickel. In his experiment, he detected 1000% excess heat. When people of Thermacore found out about this, they immediately started researching. They also found 1000% of excess heat. Now the have developed a boiler that uses the same principle to produce heat. They think they can make millions with this boiler.
| 6 | The environmental aspect of nuclear fusion |
In the beginning, thermonuclear fusion was said not to be very harmful to the environment. Only a tiny bit of nuclear waste would be produced. But in 1987, a report that was published in Great-Britain, showed that a fusion reactor with the same capacity of a fission reactor, would produce about a 100 tons of mediocre radio-active waste. This is more than the current fission reactors produce, but there wouldn’t be any highly radio-active waste. The whole amount of radio-active waste however, would still cause the same trouble as the waste of the fission reactors.
By both thermonuclear fusion and tepid fusion tritium is used. A frightening thing is that the tritium, the only radio-active element that is used, can easily replace the hydrogen in water. The tritium is very hard to capture in a reservoir (it even goes right through a metal wall), and so it could escape out of the reactor and get into the water-works. This means that there is a risk that it spreads everywhere, and even that we might drink radio-active water. Of course this is a very severe problem that especially concerns the governments.
These problems, however don’t mean the end of thermonuclear and tepid fusion, because for almost every problem, there is a solution. At this moment, scientists can actually let a single molecule move exactly the way they want, and so future techniques might be able to control the tritium and get rid of this last danger and so there is good hope for thermonuclear fusion when we look at the environmental part.
Cold fusion is the ‘clean’ forms of fusion. It is not yet clear how much radio-active waste would be produced by a reactor that uses this principle because it isn’t completely understood yet. Cold fusion doesn’t seem to produce much radiation or any waste, but we can’t draw a conclusion before scientists have completely found out what exactly happens. However, it is already clear that it won’t produce as much waste as a thermonuclear reactor.
| 7 | Conclusion |
In this paper, we have studied the three possible forms of nuclear fusion. In the second chapter, we took a closer at what nuclear fusion really is and why it releases energy. Then we studied thermonuclear fusion, the most common form of nuclear fusion. We examined the Tokamak device, the laser gun fusion and fusion with particle accelerators. After that, we went on with tepid fusion, a rather unknown form of fusion. Then we saw the most interesting, and also the most complex form of fusion: cold fusion. Finally, we looked at the environmental aspects of nuclear fusion, and saw that it isn’t as clean as scientists thought in the beginning.
With this three forms of fusion, there is a reasonable chance that at least one of them will be completed within the next century. Hopefully, this will solve the energy problems and the environmental problems that we have at this moment.
Although not all the details are worked out completely, I hope the reader gets a clear view on nuclear fusion.
Marko van Dooren
Cadbury, Deborah, ‘HORIZON - Too close to the sun’, BBC TV Productions.
Donné, A.J.H. and Oomens, A.A.M. , ‘Zon op Aarde’, Natuur en Techniek, 58, 2(1990), p. 118 - 129.
Dossche, Ward, ‘Experimenten met koude kernfusie kritisch bekeken’, Milieurama, 7, 1989, p. 38 - 39.
Even, Ludo, FYSICA voor het hoger onderwijs deel 2, Geel, 1993, derde herziene druk.
Hawkes, Nigel, ‘Blowing hot on cold’, The Times, August 10, 1989, p.4.
‘Kernfusie-onderzoek in West-Europa’, red. Sabelis, A.C., Aarde & Kosmos, 7-8 , 1982, p. 398 - 399.
Koppeschaar, Carl, ‘Nog even en er brandt op aarde een kunstzon’, KIJK, februari, 1988, p. 4 - 9.
Koppeschaar, Carl, ‘Koude kernfusie te mooi om waar te zijn?’, KIJK, augustus, 1989, p. 36 - 38.
Molkenboer, Ada, ‘Koude kernfusie: ei van Columbus of lege dop?’, Mens & Wetenschap, 4, 1989, p. 278 - 279.
Selnes, T.A. Nuclear Fusion Research, Rotterdam, July 1995.
