How are alpha particles produced and how dangerous are they?

An alpha particle is produced by the alpha decay of a radioactive nucleus. Because the nucleus is unstable a piece of it is ejected, allowing the nucleus to reach a more stable state. The piece that is ejected is the alpha particle, which is made up of a two protons […]

Assuming economically viable fusion can be achieved, could this technology be harnessed for use in spaceflight? If so, what could it mean in terms of flight speed?

We are entirely focussed here at JET on developing fusion as a source of electricity here on earth – and that is certainly challenging in its own right! As for the potential of using fusion power in spaceflight, it is certainly envisaged in many science fiction books, films etc. In […]

About 35 years ago I read a book about atomic energy. It said that human beings will need 30 years to benefit from fusion energy. It proved to be wrong. How long is the estimate now?

We have taken enormous strides in the last 30 years, but on the way discovered fresh challenges; for example, we have made incredibly hot plasma – over 100 million degrees, ten times hotter than the sun – only to discover it’s incredibly difficult to confine it! We now have created […]

Does fusion give off radiation?

The fusion reaction releases neutrons, the energy of which will be used in future power stations to heat water to heat drive the power plant. The neutrons would be quite dangerous to humans, but when the plant is turned off the production of neutrons ceases within milliseconds. The neutron bombardment […]

Since plasma is a super heated substance, will it cause the burning of the reactor and, if so, how far will the burning reach if the magnetic confinement or one of the control or safety systems fails?

The answer is one of the key advantages of fusion as a potential energy source over nuclear fission power stations – its inherent safety. Although the plasma in a tokamak is extremely hot, it is at low pressure, and so its total heat energy is not large – there is […]

Would it be best to devote a majority of resources to the Tokamak projects instead of Z pinch machines or laser type fast igniter approaches? Besides the technical spin-offs that the other approaches contribute, is the Tokamak more efficient design toward power plant production?

The tokamak is probably the most advanced fusion technology at the moment, however it has also probably had the most investment in it. All fusion approaches have their advantages and drawbacks, so it would be unwise to put all our eggs in one basket. Other possible fusion methods, inertial confinement, […]

How is it that both fission and fusion produce power? If splitting a large atom into two smaller atoms releases energy, it seems that combining two smaller atoms into one larger atom would require energy, not release it.

Yes, at first sight it doesn’t make much sense. The key is in how tightly the protons and neutrons are held together. If a nuclear reaction produces nuclei that are more tightly bound than the originals then energy will be produced, if not you will need to put energy in […]

How do fission and fusion reactions compare?

In fission, energy is gained by splitting apart heavy atoms (uranium), into smaller atoms (such as iodine, caesium, strontium, xenon and barium, to name just a few) whereas fusion is combining light atoms, (in current experiments two isotopes of hydrogen, deuterium and tritium), which forms a heavier one (helium). Both […]

Tell me about the ways to heat plasmas.

In magnetically confined plasmas that we study in JET, there are three main ways of heating the plasma. The first is to use the strong electric current that is generated in the plasma (to help its stability and control) – this is known as Ohmic heating and heats the plasma […]

How does fusion work?

Fusion releases energy when the nuclei of two forms of hydrogen (in our case, we use deuterium and tritium) are collided together at such high velocities that they stick together or fuse. Shortly after this, they break apart, forming a neutron and a helium nucleus. In this conversion a small […]

How is energy extracted from fusion reactors?

The energy out from fusion is the form of fast energetic neutrons. We have to slow these fast neutrons down, so we allow them to penetrate a blanket of lithium surrounding the plasma. As they bombard the lithium atoms in the blanket, they slow down and the blanket will heat up, […]

Why is it important that a change of flux happens in the poloidal field coil?

The rate of flux change in the poloidal field coil produces an electromagnetic field (EMF) in the vacuum chamber which must be large enough to lead to a breakdown of hydrogen. Regarding the breakdown value, two pages of assistance are here: The EMF in the vacuum chamber drives the current around […]

Is it possible to create another sun by fusion?

Yes, in some ways we are trying to create another sun using fusion, because inside our tokamak devices a very similar reaction to the sun is going on – the fusion of hydrogen in helium – and in the process developing lots of energy. However our fusion experiments are not […]

Why are the impurities and alpha particles removed by the divertor in a tokamak, but neither deuterium nor tritium?

The natural flow of particles towards the bottom of the plasma ensures that actually most different types (deuterium, tritium, alpha particles) will be pumped away – the divertor is not selective. The main purpose, however, is that deuterium and tritium have fused at this point before this happens – so largely helium […]

Once ITER is up and running, how much deuterium and tritium will it use over a period such as a year and how long will the supplies last?

The deuterium we gain from seawater is abundantly available. We get the tritium for ITER from the Candu reactor in Canada. For future machines, a technology called tritium breeding is being developed. http://www.iter.org/newsline/167/631 http://www.iter.org/newsline/96/1319 http://www.iter.org/mach/tritiumbreeding  

What is responsible for the initial breakdown of hydrogen?

The answer is the poloidal coil. The reason is that the poloidal coil is operating as the primary coil of a transformer, and the secondary coil is the gas itself. The changing current in the poloidal coil induces a voltage around the torus, which needs to be high enough to […]

Resonance heating – Is the plasma heated (and designed) with exact “harmonics” of the plasma wavelength’s etc.?

There are a number of heating methods used for the plasma based on electromagnetic waves, ion cyclotron resonant heating (ICRH), and lower hybrid current drive (LHCD). For ICRH yes,  they do couple energy in using a resonant frequency of the plasma – the cyclotron frequency of the ions. For lower […]

Is JET efficient? How efficient?

JET is an experiment – and is not advanced enough or powerful (big) enough to create large amounts of fusion power. The best it has done is make 16MW of fusion power out for a short period (a second or so) – which was about 65 % of the power […]

Is JET dangerous and hazardous to the environment?

The fusion process is very safe. The very hot gas or plasma of fuels is contained in a vacuum vessel and kept from the vessel walls by powerful magnetic fields. Although the plasma is very hot (150 millions degrees Celsius, ten times hotter than the core of the Sun), there […]

How many fusion reactors are we bound to see in the future?

Realistically, we should be in a position to build commercial reactors in the period after 2050 – and they will be large (1-2 GW). This will not be done by research, but by the industry. A future mix of fusion, advanced fission and renewables would be the best hope for […]

If something were to go wrong, would it be an extremely dangerous reaction such as a fusion bomb?

Fusion is one of the processes involved in a nuclear weapon. But the fusion process we are perfecting, is entirely different. We employ very small amounts of fuel – and if there are any problems, the reaction extinguishes. In essence, we are trying to control the reaction; in contrast, in […]

How large are current fusion experiments? Will they get any bigger?

The vessel in JET is 90 cubic metres – in ITER it will be ten times bigger and maybe 2,000 – 3,000 cubic metres in a commercial reactor.  In terms of physical size, it will look like a conventional fossil fuel or fission power station.

How much does it cost to build a reactor like JET?

When JET was built it cost about ₤200 – 300 million – but that was in 1993. To rebuild now would cost around ₤1 billion.

super conductivity at room temperature

Whilst fusion will benefit hugely from discovering materials that are routing superconducting at room temperature, this is not an area we are researching significantly. A breakthrough in this area would make future fusion power plants much more efficient and the transmission of electricity would be transformed.

Why is heavy hydrogen not used at a high pressure, knowing that a vacuum is needed to prevent the interaction of the heavy hydrogen with any other molecules/ions?

The vacuum inside a tokamak vessel is required to prevent any impurities from ruining the plasma performance.  The presence of significant oxygen, nitrogen molecules etc will increase dramatically the radiation observed from the plasma and can prevent the plasma being sustained at all.  You are correct that it would be […]

Where does the change in mass during the reaction come from and which piece of mass is converted into energy if the number of protons and neutrons is equal on each side of the fusion reaction?

The change in mass comes about because the protons and neutrons are bound a little more tightly together. You cannot determine which piece of mass is lost – it only happens as a result of the combination of protons and neutrons that make that atoms. If you tried to separate […]

Does the beryllium wall on JET act like a neutron multiplier? If it does then surely turning atoms in the wall into He can’t be good for the lifetime of the wall. If it doesn’t then why not?

Not at all. Beryllium is on the wall of JET (a very thin layer) to mitigate erosion as much as possible. The level of sputtering of beryllium is not very high, and since it is a light element its presence in the plasma is relatively tolerated. Beryllium is an option for neutron […]

How are waste materials removed?

In the fusion process the energy will be gained using the two isotopes of hydrogen: deuterium and the radio active tritium. That way the main by-product in a future power station will be helium – a non-radioactive gas which  will be pumped out of the vessel and store on site. As […]

I’m very interested in plasma physics and studying in Great Britain. Which University is active in the field?

We have the closest links with the University of York, Imperial College London and Warwick University in terms of plasma physics.  In materials research, with University of Oxford, Bristol University and Birmingham University.

What kind of qualifications would one need to help in the research and engineering behind projects like ITER and JET?

Almost all scientists in fusion research have physics degrees – then some will study to do a PhD – often at a Fusion Association as well with partner universities. Engineers in the field are more varied – electrical, mechanical – some civil, control.  Also, fusion research requires IT professionals. Fusion research needs […]

Compare the use of fission and fusion as sources of energy

Using nuclear fission and fusion for generating electricity requires very different technologies and engineering. With fission, the splitting of heavy nuclei (uranium, plutonium) happens quite easily – and most reactions accelerate (i.e. produce more neutrons for splitting more atoms per reaction). So harnessing fission (in conventional nuclear power stations) needs […]

What is fission and fusion?

Fission is the splitting of heavy nuclei (such as uranium) – in two smaller nuclei. This process needs less energy to ‘bind’ them together – so energy is released. Fission happens quite easily – and is used to generate electricity in conventional nuclear power stations. Fusion on the other hand, […]

What are the main methods used to heat the fuel to the temperatures necessary for fusion to occur?

In tokamaks, there are three main heating methods 1. Passing a current through the plasma accelerates the charged nuclei and electrons and also creates a confining field around the plasma (plasma is just a name for a very hot gas which has become electrically chanrged) 2. We also use powerful […]

How are alpha particles produced and how dangerous are they?

An alpha particle is produced by the alpha decay of a radioactive nucleus. Because the nucleus is unstable a piece of it is ejected, allowing the nucleus to reach a more stable state. The piece that is ejected is the alpha particle, which is made up of a two protons […]

If a superconductor were discovered that could operate at room temperature, without having to be cooled cryogenically, what would the potential economic savings be in the production and maintenance of tokamaks?

Of course the details would depend on the properties of the superconductor. If it had just the same properties as Niobium Tin, then you might save around 100 million dollars in plant costs (this is just a round number of course) and about 10 million a year on running costs, which […]

With the work that has been done since 1997, what do you estimate would be the Q value if you did use full power?

Firstly we do use full power, in terms of input power. We have recently upgraded our beam power, and injected a record 26 MW late last 2012. This should be pushed at least another 4 MW during 2013 after maintenance shutdown. What we do not do often is to use […]

How far does alpha radiation travel and what material will absorb it?

The range of alpha’s in air depends upon their energy but in any case the vast majority are stopped by very thin layers of materials such as paper or even people’s skin! The question on precautions for handling sources is far too general to be answered simply. Generally the principles […]

What was the cost of construction of JET?

198.8 M European Units of Account (EUA – predecessor to the Euro). JET was completed on time and on budget in 1983.

What is the Q-value for JET?

Most of the time we do not use the full-power fuel, deuterium/tritium mixture, however in our high power experiments in 1997 with this mixture the maximum output was 16.1 MW, from about 24 MW input power, giving a Q value of about 0.65.

How much energy from the 14.1 MeV neutrons is used to split the lithium? Doesn’t this energy requirement diminish the reactor’s actual gross power output?

The Li-7 transmutation reaction does have a threshold energy, that the neutron needs to have for the reaction to occur, but the Li-6 reaction can occur at any neutron energy. However in both reactions energy is released, the exact amount depending on the nature (energy, velocity, etc) of the incident […]

What isotopes of lithium are best to use in the blanket for generating tritium?

There are transmutation reactions from both Li-6 and Li-7 to tritium however the Li-6 reaction is the dominant pathway.

Where does the plasma colour come from?

The colour comes from the fuel, which is basically hydrogen. Hydrogen gives out two different colours, a strong red and aqua-blue, which combine to give the pink colour that shows up in most pictures. The two colours come from specific transitions of the hydrogen atom’s electron between different energy levels […]

When will fusion power be used in ships and how much of a reduction in size would it take?

As fusion power generation is still in the research phase it is hard to say whether it will ever be feasible for ships. At this stage plans to achieve significant output power from fusion hinge on making the vessel larger, to overcome the energy losses from plasma: we expect that […]

Would it be possible to produce power, using He-3 and today’s fusion reactors, that could be put into the grid?

The first thing to note is that fusion reactors – producing commercial electricity – are not ready yet.  We are still researching how to make this technology work in an economically and efficient way.  The first true fusion power stations are probably 30 years away. All our work is focussed […]

Question who was the general contractor responsible for the construction of the JET facility?

There was not one general contractor for the construction of JET in the early 1980s.  As a European project, the project team placed orders with many contractors all over Europe to build parts of the device (vacuum vessel, magnetic coils etc).

As the current is driven by transformer action, it can only be driven in pulses. In between pulses, when there is no current and so no poloidal field, what happens to the plasma?

At present, the current in the plasma, which is essential for plasma heating and providing poloidal field for confinement, is provided by the discharge of a transformer. The pulsed nature of the discharge is due to the fact that the transformer can only operate in one polarity. If it operated […]

Ninety square metres seems like a very large volume for the plasma torus. I had expected far greater constriction would be necessary to achieve the Lawson criterion plasma density.

The Lawson criteria deal with the temperature, density and confinement time required to achieve energy gain from fusion. There is no limit to the volume; for example, the sun is a fusion reactor with a very large volume! In fact a larger volume is an advantage as it means a […]

Are members of the public allowed to visit any of the facilities?

We run a series of open evenings through the year, approximately monthly, which enable the public (individuals or groups) to come and visit the JET and MAST fusion experiments. They are very popular, so book early!

What temperatures have been recorded in the walls of the vessel during operation?

In JET, the vessel walls are maintained at a high temperature of 325 degrees Celsius all the time. The main increase in temperature during plasma operations is noted in the lower (divertor) region where the wall tiles are in contact with the plasma. Typically, temperatures here would rise to 1000 […]

What is the thickness of the lithium blanket in JET and in ITER?

JET does not have a lithium blanket. It is an experimental facility, and not a power reactor, so it is focussed on exploring the behaviour of plasma, rather than producing a long stable output. Most of the time it does not even run with tritium, as deuterium only plasma is […]

Is the plasma chamber evacuated? To what pressure? Do the tiny amounts of deuterium and tritium alter the pressure?

The plasma chamber in a tokamak like JET has to be pumped down to a very good vacuum before decent plasma can be created. Any impurities, for example, atmospheric gases such as oxygen or nitrogen, need to be removed to keep the plasma stable. A typical base pressure inside JET […]

If a tokamak had been working for several years are there issues with radiation and closing the site down?

Fusion processes do involve radioactive materials. A device like ITER, or the fusion powerplants that will follow, will become radioactive through two mechanisms. One of the fuels – tritium – which is a heavy isotope of hydrogen, is radioactive. Inevitably, some tritium gets stored in the infrastructure of the tokamak, […]

If ITER or JET were fired up and someone was standing nearby, what effects in respect of electromagnetic and other radiation are there on the person?

There are reasons we do not let anyone near a device like JET or ITER when it is operating. The plasma ejects significant amounts of X-rays  that would be harmful to anyone standing close to it. Also, very high voltage (10,000s of volts) circuits are used to feed the powerful […]

How much time did you spend by changing all the wall to the ITER-Like Wall.

We have just finished a major refurbishment of the JET machine, where all the old carbon tiles have been removed and replaced with new beryllium and tungsten tiles, of the type planned for use in ITER. This was mostly done by our advanced handling robotic system, and took around 18 […]

Will we need any complement to fusion power?

Fusion has many advantages over existing power generation methods. Firstly it has widely abundant and cheap fuels, which could supply us for millions of years. Secondly it has the ability to operate in a base load capacity, which is not easy for generation methods based on infrequent sources, such as […]

Assuming economically viable fusion can be achieved, could this technology be harnessed for use in spaceflight? If so, what could it mean in terms of flight speed?

We are entirely focussed here at JET on developing fusion as a source of electricity here on earth – and that is certainly challenging in its own right! As for the potential of using fusion power in spaceflight, it is certainly envisaged in many science fiction books, films etc. In […]

Have there been any experiments in using a rotating magnetic field to induce a twist to the plasma flow, i.e. inducing turbulence into the toroidal flow? The induced turbulence may make the whole system more stable.

One of the hot topics in plasma physics is how increased turbulent flows can improve plasma stability. Indeed on the MAST experiment here at Culham, we have an active series of experiments studying how increased plasma flow (up to supersonic speeds) in toroidal and poloidal directions affects plasma stability and […]

How long is the time between pulses at JET? Is this time typically longer than the limit imposed by the plasma physics?

The time between pulses is normally more than 20 minutes and is usually determined by data collection and analysis and preparation for the next pulse. The main reason that JET has to operate in pulsed mode is because of the operation of the electromagnets that provide the magnetic field. To […]

What is the time limit to a pulse imposed by the heating of the copper coils?

The operation of a tokamak relies on the hot plasma being confined within a magnetic bottle, created by large electromagnets. At JET, the electromagnets are made of copper, and carry currents of many thousands of amperes, which generate large amounts of heat because of their resistive losses – this heat […]

How much of the toroidal coils resistive loss (during a pulse) is removed by the water cooling system, if any? Or is the cooling used only to shorten the time needed to cool the coils enough for the next pulse?

All of the resistive loss is removed by the cooling system, which runs continuously. The pulse lasts about 30 seconds and the cooling time is about 20 minutes so about 2% of the loss is removed during the pulse.

What is the resistive loss (power and total for each pulse) in the toroidal coil magnet coils?

The total power required to run the coils at JET is about 700 MW, of which 400 MW is consumed by the toroidal magnets. The losses in these coils are about 280 MW, which totals to energy losses of 5.5 GJ per pulse. Future fusion facilities such as ITER will […]

How much copper do the toroidal coils contain?

The toroidal coils weigh about 380 tonnes, about the weight of a Jumbo Jet

How is the plasma initially formed from the cool material?

The gaseous fuel – either deuterium or a deuterium/tritium mix – are released into the JET vessel at room temperature. A very large voltage is applied by the toroidal coil, which causes the atoms to break down, as happens in lightning: the energy strips the electrons from the nuclei , […]

I can’t find anything about progress of how the reactor is doing, and of major breakthroughs getting close to actually getting a real fusion reactor running?

Fusion research is a long term project, with a target of working fusion reactors putting electricity on the grid in about 30 years. JET is not a power station, it is an experimental device which is playing a key role in answering technical and engineering questions, such as how best […]

To what temperature does the ohmic heating get the plasma?

There are several ways that we use to heat the plasma – first passing a large current through it (ohmic heating) and then microwave and neutral beam heating methods. Ohmic heating schemes typically get the plasma to 40-50 million degrees Celsius. However they cannot go much further as the effectiveness […]

Circa 1997 I machined 150 components from graphite for JET. Could you tell me what they would have been used for?

The graphite components you worked on would almost certainly have been used to line the inner walls of the JET vessel. These walls are the first contact point with the very hot fusion plasma in JET, and need to be made from tough heat-resistant materials. Hence graphite and CFC tiles […]

Why do you try fusion in a vacuum when, as you all say, fusion happens in the sun not in the vacuum of space. Should you not try fusion under pressure as that is how it takes place in the sun?

You are correct that fusion takes place at high pressure in the core of the Sun, and not actually in the surrounding vacuum; gravity is what holds the plasma together. Strangely enough, the sun is a very inefficient fusion reactor, producing only 1 watt per cubic metre – luckily it […]

How much will constructing a plant that creates fusion power cost?

The next step for fusion research is the construction of the ITER, a large international fusion experiment in the south of France, ITER will test the materials, engineering and science which will enable the first commercial fusion plants to be built. The first of these is expected to cost in […]

About 35 years ago I read a book about atomic energy. It said that human beings will need 30 years to benefit from fusion energy. It proved to be wrong. How long is the estimate now?

We have taken enormous strides in the last 30 years, but on the way discovered fresh challenges; for example, we have made incredibly hot plasma – over 100 million degrees, ten times hotter than the sun – only to discover it’s incredibly difficult to confine it! We now have created […]

What is the temperature generated in a tokamak reactor? How can the inner wall material resist that temperature?

In order for fusion to occur in the very hot gas – or plasma – we create inside JET, the plasma must be heated to temperatures in excess of 150 million degrees Celsius. In order to achieve this, the plasma is actively held away from the walls of the tokamak […]

On a future fusion device a lithium-6 blanket will be used to collect neutrons and remove heat. This heat exchanger will then heat water to steam, but what chemical is used in this process? (as water and lithium is not a good mix for pipework)

The next step fusion device, ITER, which is being constructed in France, will test blanket modules . As well as absorbing the heat from the reaction, the idea is to also wqithin the blanket breed tritium, which is rare and expensive, but is formed when neutrons bombard lithium. The design […]

I am interested to know how the internals of the machine are not damaged from the immense heat of the plasma. I am aware that there is magnetic confinement of the plasma, but does it not radiate heat?

You are correct that the very hot (150 million degrees Celsius) plasma in JET is held away from the walls of the container using very powerful magnetic fields. However, if the plasma becomes unstable it can break free from this confinement and hit the walls of the container, in the […]

What is the annual electricity consumption of the JET facility?

Annual consumption is very dependent on whether JET is operational or in shutdown. The peak of consumption here is during a 300s JET pulse – where over 300 megawatts of electrical power is pulled from the grid, and up to 400 megawatts is supplied from two large flywheels located here […]

How is the plasma heated, are lasers now used or are the magnetic fields in a transformer like set up still how it works?

There are a number of ways that we heat the plasma. One of the main ways is using a transformer to induce a large current in the plasma (termed Ohmic heating). We also use powerful microwave systems (using the same principles as a microwave oven) and intense beams of fast […]

How is the plasma contained in the ‘cage’, is it via superimposed magnetic fields?

Yes. In tokamak devices such as JET, we do use magnetic fields to confine and contain the plasma away for the walls of the vessel. These are a combination of fields that the plasma creates itself and external ones we apply. We have 32 D-shaped copper coils around the vessel, […]

a) What would be the best undergraduate degree to be on CCFE’s Graduate Schemes? b) If I achieve a MSci Physics, what opportunities would there be for me if I wish to seek employment at CCFE? c) The CCFE’s Graduate Schemes imply that you are required to have an engineering degree. Why aren’t there schemes by CCFE that require a Physics degree?

The CCFE Graduate Scheme concentrates on recruitment of engineers at present  – as that is where our most acute staff shortages are at present.  Of course, most of the scientists here are physicists – with physics degrees, MScs and PhDs – so your thoughts are along the right lines. It is hard […]

I am a chemistry student and I’m investigating the options available for my future career. I am hoping to pursue a career in the nuclear/quantum sciences, like those available at Culham, but I am finding that most vacancies in these fields require a background in either maths or physics. Could you offer any advice for those in my position?

You are correct that most careers here require a physics background – or some kind of engineering.  It is also worth pointing out that vacancies are few and far between at present – as we go through a bit of a financial squeeze. However, there are in principle areas of […]

Has there been any conclusion/theories why the power generated by this process is less than the power required to create the nuclear reaction?

We definitely achieve fusion reactions here at JET, it’s just that so far we have needed more power to get it going than we have created. The power generated in JET (best so far = 16 megawatts) is limited to a level much lower than it could be by the […]

Is there a point in the circulation of deuterium and tritium where the stream is shock pinched such as in a magnetic venturi?

The plasma is certainly magnetically squeezed somewhat inside JET. However the magnetic field, and therefore the plasma, is more or less symmetric around the torus, there are no pinch points. If the flow of nuclei becomes really constricted, the plasma stability can start to become adversely affected.

What is the most specific figure that makes the machine in your institution different from the rest of the tokamaks?

The most obvious thing is that it is the biggest fusion tokamak in the world that is currently operational. It is also the only one which can actually observe thermal fusion reactions, as it is the only existing device able to run with tritium – all others are deuterium only. […]

What is the budget per year for the JET research programme?

It is of the order £60 million per year.  This is contributed in various amounts by the European Commission, and through EURATOM each of the fusion programmes in EU member countries including Switzerland as an associated member to EFDA.

I am thinking of doing an extended research project on Fusion, including confinement techniques like magnetic and inertial. Could you point me in the direction of some books (or other) for further, detailed reading?

There is a lot of information on our websites : EFDA and JET, in particular the Focus On section) and CCFE. Also ITER has an extensive website. In terms of more detailed books, there is a book all about tokamaks – Tokamaks by John Wesson.  This goes into real detail about […]

How much power is needed to start the reactor and to keep it working?

JET consumes large amounts of power – for fusion to occur we need to create and maintain plasma at extremely high temperatures. Additionally we need to contain the plasma by energising large magnetic coils. In total, when JET runs, it consumes 700 – 800 MW of electrical power (the equivalent […]

You state that a fusion reactor would generate about 1500 Megawatts but what is the time span in which that amount is produced?

A fusion powerplant will indeed produce about 1500 megawatts of power (similar to an average conventional fossil fuel power station) and will produce this amount of power all the time it is operational. Watts are a measure of energy per second – in other words, this powerplant will produce 1500 […]

How much electricity could be produced in the best scenario?

We have scientists and engineers here working on possible future fusion reactor designs and the largest capacity considered so far is about 3 gigawatts (this compares to typical current coal-fired stations at 1 – 2 gigawatts). In theory, the larger the reactor, the more efficiently it would operate, and the […]

Even if you could sustain fusion for prolonged periods, how do you extract power from the reactor?

A nuclear fusion power plant would be no different from a conventional power plant in the sense that there would be a heat exchanger connected to a steam generator to turbines. The heat would be extracted from the lithium “blanket” inside the reactor wall which would absorb the neutrons created […]

How large might fusion reactors become once the technology has been proven?

It is true to say that the bigger the plasma, the better the confinement and the bigger the fusion gain factor. However, increasing the plasma temperature and density also achieve an increase in gain factor. It is envisaged that future fusion powerplants would occupy buildings no bigger than presently house […]

If the lithium blanket reacts to form deuterium and tritium will it eventually get used up and need replacement and might the lithium melt?

There would be enough lithium in a typical blanket to last the lifetime of a powerplant (the blanket is large, completely surrounding the plasma). However, a blanket would have to be replaced in a powerplant about every 5-10 years as they will be gradually damaged from the intense neutron bombardment […]

What is a lithium blanket and how does it work? What happens to the neutrons after they’re absorbed by the lithium blanket?

The blanket is a layer surrounding the vessel in a fusion powerplant. It will absorb the energy from the fusion neutrons produced in the plasma, boiling water via a heat exchanger, which will be used to drive a steam turbine and produce electricity. The proposal is to embed lithium in […]

What would be the soonest that fusion power could be operable in Europe if funding were increased, and energy funding diverted from fossil fuel energy research? And if the fusion research projects of the USA, EU, and Japan were combined, what is the soonest fusion power could be efficiently operated?

The next step from JET (and the other tokamak research being undertaken around the world) is a device called ITER, an international tokamak project, 2-3 times bigger than JET, costing several billion pounds and capable of producing significantly more fusion power for longer periods. This will demonstrate the feasibility of […]

When are we going to use fusion as a source of energy? I remember 50 years ago they were talking about it, and so far I have not seen any of the present nuclear reactors replaced by fusion reactors. What is the problem?

The problem was the unrealistic expectations regarding our abilities to control the extreme temperatures in which fusion can burn (hundreds of millions of degrees Celsius). As it turns out it was easier to create the high temperatures than it was to control the plasma we had created. However we have […]

How do you plan on making ITER’s coils superconducting?

The magnetic field coils planned for use on ITER and potential fusion powerplants will use superconducting materials, such as alloys of niobium and tin, or niobium and titanium, which become superconductors below -264 degrees Celsius. The idea is that the ITER vessel and its coils will be surrounded (in fact […]

Since ITER is expected to produce 10 times the power consumed, does this not mean that the substance produced and reused will by further extrapolation reduce the power needed by a reduction of 10? And this reduction lead to a further reduction of 10 and so on until almost no power is used?

ITER will generate fusion power that is ten times more than the power used to directly heat the plasma. Additional power is required for the magnetic field coils, although this will be much reduced at ITER as they will be superconducting. Nonetheless, as you suggest, in the fusion process there […]

The projected time for a fully operational reactor is 30-50 years; by this point renewables (solar PV, wind etc) and hydrogen fuel (with its use in fuel cells) are predicted to be completely commercially viable and have large market shares. How do you see fusion’s ability to compete with these inherently ‘clean’ technologies when at that point in time they will be cost-effective and a large part of the power infrastructure? Whilst being a revolutionary technology, will fusion be too late and too expensive when more ‘environmentally friendly’ solutions are already in place?

It is true that fusion power plants are 30-40 years in the future and, by that time, renewable energy sources will probably have a greater share of the energy market. It is difficult to say, however, whether they will be providing the majority of the electrical power in most countries. […]

Is there any possible way that we can prove the feasibility of fusion by not building this large ITER reactor?

The feasibility, in terms of the way the plasma behaves, is pretty well understood (from experiments on JET and other tokamaks) and scientists are confident that larger, hotter plasmas (such as ITER) will not only produce much more fusion power, but will remain stable for long periods of time. There […]

Where is ITER being built?

ITER is being built in Cadarache in southern France. Cadarache is one of the major sites of the France’s Commissariat a l’Energie Atomique, and includes the French tokamak, Tore Supra.

What is ITER and how is it supposed to work?

ITER is a fusion experiment like JET – a tokamak – being built in the south of France. It will be 2 – 3 times larger than JET, and is planned to commence operation in 2019. The research in tokamaks, and JET especially, has given us confidence that fusion power […]

Is there a connection between nuclear fusion research and atomic bombs?

Firstly, we do not endorse the research, development or production of nuclear weapons in any form. The reaction that we seek to make use of for fusion is between the nuclei of atoms, and its large energy release can be used for weapons, however, that is where the connection ends, […]

Is fusion less or more expensive than fission?

Studies have concluded that the cost of producing fusion power will be roughly the same as clean coal or fission, as the overall process is similar – a reaction heats water which turns a turbine to generate electricity. Fusion does differ slightly from fission in that the reaction requires more […]

Does fusion give off radiation?

The fusion reaction releases neutrons, the energy of which will be used in future power stations to heat water to heat drive the power plant. The neutrons would be quite dangerous to humans, but when the plant is turned off the production of neutrons ceases within milliseconds. The neutron bombardment […]

Is more power currently generated by fusion or by fission?

Fusion is in the research stage, with the first power plant demonstration planned for construction around 2030. The current and immediate future fusion facilities, such as JET and ITER, are experiments, and do not have the infrastructure for generating power. Design and planning indicates that fusion power plants will be […]

Could you please explain some of the safety measures that assure against accidents that may occur during a fusion reaction?

Unlike nuclear fission, the nuclear fusion reaction in a tokamak is an inherently safe reaction. The reasons that have made fusion so difficult to achieve to date are the same ones that make it safe: it is a finely balanced reaction which is very sensitive to the conditions – the […]

Since plasma is a super heated substance, will it cause the burning of the reactor and, if so, how far will the burning reach if the magnetic confinement or one of the control or safety systems fails?

The answer is one of the key advantages of fusion as a potential energy source over nuclear fission power stations – its inherent safety. Although the plasma in a tokamak is extremely hot, it is at low pressure, and so its total heat energy is not large – there is […]

Is EFDA conducting the only serious research into fusion power? I read somewhere that the USA’s program was shutdown during the Reagan administration. Has the USA (other than its physicists) lost interest in fusion power?

Europe has for a long time been the leader in fusion research. EFDA laboratories all across Europe are very active in magnetic confinement fusion research both in their domestic programmes and via the EFDA-JET collaboration. The EU has been investing almost twice as much into fusion research as Japan or […]

Why aren’t governments funding this research a lot more? Nearly free limitless power coupled with little environmental impact would be a great boon to our world. Clearly the science is sound – we can look up into the sky and see that it works, that large glowing orb is powered by the same method. Could it be that governments are afraid that the loss of dependence upon fossil fuels could hurt the global economy as they collect huge sums of money from taxing oil companies and end users (we the people) of fossil fuels?

This is difficult to answer. The conversion to a power generation infrastructure based on fusion would require a large investment, which is perhaps why governments are waiting for more solid proof that fusion will work. We believe this will come from ITER (the successor to JET, currently built in Cadarache […]

Why, if we have fission, do we need fusion?

Energy demands will increase even more dramatically over the next fifty years as the developing world comes to expect the same standard of living as the industrialised countries. Nuclear fission is a possible energy source, which has the advantage of having a negligible carbon footprint. However nuclear fusion, is even […]

Who will use fusion power? What precautions will be taken to ensure that one group of people can’t control global fusion energy?

All developments in fusion technology are published in scientific journals, and therefore are in the public domain. Thus it should be commercially available to any country as an alternative to conventional forms of energy production. Indeed ITER, the next generation of fusion experiment is funded by seven countries (EU, USA, […]

But aren’t there any real downsides to fusion power? It can’t be all great, can it?

There are downsides to fusion power but we believe the potential advantages (almost limitless fuel supply, no greenhouse gas emission, no dangerous waste products or possibility of explosion) heavily outweigh them. The main downside is that it is difficult to achieve – hence we are still researching the concept rather […]

Would it be best to devote a majority of resources to the Tokamak projects instead of Z pinch machines or laser type fast igniter approaches? Besides the technical spin-offs that the other approaches contribute, is the Tokamak more efficient design toward power plant production?

The tokamak is probably the most advanced fusion technology at the moment, however it has also probably had the most investment in it. All fusion approaches have their advantages and drawbacks, so it would be unwise to put all our eggs in one basket. Other possible fusion methods, inertial confinement, […]

I would think that ITER would require a substantial amount more power to produce the plasma than JET. If you were to create a smaller reactor you would need less energy to run it, thus allowing for it to run longer which should allow you to study it better. If you make it smaller you can exert more magnetic force to contain and heat the plasma and possibly make it self sustaining. Shouldn’t we be looking at smaller tokamaks?

It is true that ITER will require more power to heat the plasma than JET as the plasma is bigger and will need to be hotter. However, the confinement is key: ITER, as it is hotter and bigger, will lose proportionately less energy than JET and so will produce a […]

How does plasma heat if all the particles are travelling in the same direction?

The basic heating system in a fusion reactor is electromagnetic: Huge coils are electrified, which create a magnetic field that drives the plasma around the donut-shaped tokamak, known as the plasma current. However this plasma current is not every charged particle marching in step. The plasma is at an extremely […]

Would a Tokamak work better in zero/low gravity conditions?

Gravity has very little effect on the dynamics and/or stability of the plasma so operation of a tokamak in zero gravity would make little difference. The particles are moving at such high speeds, because of their heat, that they experience much stronger magnetic forces than gravitational.

How much more energy will it take a Tokamak over the “breakeven point” to actually produce power due to loss of energy in the processes of electricity production?

Breakeven is achieved when the energy from fusion reactions is larger than the energy required to sustain the plasma. So far JET has reached about 60 percent of this level, but in ITER we expect to exceed breakeven by a factor of ten. In the process of converting the energy […]

What are the minor and major radii of the plasma?

The major radius of a tokamak plasma is the radius of the ring of the tokamak, measured from the centre of the “donut hole” down the centre of the device to the centre of the plasma. The minor radius is the radius of the cross section of the chamber – […]

Are there any other tokamaks in operation around the world?

There are many tokamaks in operation around the world, all contributing to international efforts to realise commercial fusion power. As well as JET, there are many other tokamaks in Europe, which are part of the EFDA agreement. There are also tokamaks operating in the USA and Japan, and smaller tokamak […]

How is it that both fission and fusion produce power? If splitting a large atom into two smaller atoms releases energy, it seems that combining two smaller atoms into one larger atom would require energy, not release it.

Yes, at first sight it doesn’t make much sense. The key is in how tightly the protons and neutrons are held together. If a nuclear reaction produces nuclei that are more tightly bound than the originals then energy will be produced, if not you will need to put energy in […]

How do fission and fusion reactions compare?

In fission, energy is gained by splitting apart heavy atoms (uranium), into smaller atoms (such as iodine, caesium, strontium, xenon and barium, to name just a few) whereas fusion is combining light atoms, (in current experiments two isotopes of hydrogen, deuterium and tritium), which forms a heavier one (helium). Both […]

How are only the impurities (particularly helium ash) removed, when they are all charged? Wouldn’t any sort of flow also take some of the plasma into the divertor?

There is not a perfect confinement of the plasma; all plasma components (including the fuel – deuterium and tritium) diffuse across the magnetic field. This means that the divertor actually is receiving flow of all plasma components, ie fuel, helium ash, and impurities. Also, only a very tiny percentage of […]

At what point during the fusion process do the helium nuclei stop adding to plasma heating and become an impurity to be removed?

About 20% of the net energy gained from the fusion reaction is carried by the newly-created helium nucleus – the remaining 80% is carried by the neutron which, because it is not charged can escape the confining magnetic field. The net energy gained by the helium ions will remain within […]

I read somewhere that the energy released by the tritium-deuterium fusion reaction is given by the strong force. Could you explain this more clearly?

Physicists have worked out that all the interactions in the universe are governed by only four different forces, only two of which we see in every day life: gravity and electromagnetism (sometimes called the coulomb force). The other two, imaginatively named the “strong” force and the “weak” force come into […]

Incredibly high temperatures and pressures to produce “random” collisions resulting in fusion seems difficult to sustain, and to have limitations. Has there been much research into more controlled methods of bringing nuclei together in fusion? For example, head on ion beam collision?

It is true that the fusion collisions in the plasma in a tokamak are essentially random, although due to the high plasma ion temperatures, these collision are quite frequent. The big challenge is to maintain the high temperature in these plasmas for a long enough confinement time (i.e. the time […]

Could you please specify the temperature required for a Fission (not Fusion) reaction of Deuterium and Tritium?

FIssion is splitting the nucleus – an effective energy source for very large elements, such as uranium, especially if they have unstable nuclei. Deuterium and tritium (which are very light nuclei) would be almost impossible to split. No energy would be released, instead you would have to inject energy. This […]

Tell me about the ways to heat plasmas.

In magnetically confined plasmas that we study in JET, there are three main ways of heating the plasma. The first is to use the strong electric current that is generated in the plasma (to help its stability and control) – this is known as Ohmic heating and heats the plasma […]

How does fusion work?

Fusion releases energy when the nuclei of two forms of hydrogen (in our case, we use deuterium and tritium) are collided together at such high velocities that they stick together or fuse. Shortly after this, they break apart, forming a neutron and a helium nucleus. In this conversion a small […]

Is research at JET still aimed at the ultimate goal of commercial energy production?

Yes. Results from JET and other tokamaks around the world have given scientists tremendous confidence that they can control and confine the plasma sufficiently that ITER will deliver significant fusion power output. ITER will nonetheless still be an experimental facility. Plans are already afoot to begin work on the first […]

How is JET funded?

The funding for EFDA-JET is spread across the whole of Europe. This supports the operation and maintenance of the tokamak (undertaken by CCFE on behalf of Europe) and the undertaking of experiments by groups of scientists from EFDA laboratories all over Europe.

If the plasma is 100 million degrees, how do you get all those pictures?

There are many ports into the vessel that allow heating, cooling, fuel, vacuum or diagnostic systems access to the chamber. The pictures of the plasma are taken through ports with transparent glass, by fast framing CCD cameras (the latest ones digitally) positioned outside the vessel. It is worth noting that […]

Tell me about the temperatures achieved at JET and in fusion reactors.

In the JET tokamak plasma is contained in a doughnut shaped vessel and is heated up by (amongst other methods) passing a current through it. Temperatures around 100 million degrees C have been achieved and fusion (albeit at a relatively low level) has been observed. An eventual fusion power plant […]

When using neutral beams to heat up the plasma do they not pollute the plasma and cause it to disrupt and how do you accelerate these neutral atoms?

Neutral beams atoms do not pollute the plasma – they will be Deuterium atoms that will actually fuel the fusion reaction and increase it by making the background fusion ions hotter and increase their density (via collisions and ionisation). The energetic neutral atoms are created by first accelerating a beam […]

I recently heard a sort-of scientific urban myth that at some point during its operation the plasma inside the torus touched the top and the whole thing jumped up in the air. Is there any truth to this story?

Normally in JET, the plasma is controlled (by powerful magnetic fields) so that it stays away from the walls of the vessel. In this way the plasma can be sustained and heated to fusion temperatures. However,if the magnetic field system is unable to control the movement of the plasma for […]

What do the central solenoid, TF, PF and divertor coils do?

The hot plasma created in the tokamak (such as JET) needs to be confined and controlled in order for sustained fusion to occur. The solenoid, which is positioned around the plasma, induces a powerful electric current in the plasma, thus heating the plasma up (much as a wire is heated […]

Could you tell me how the magnetic fields contain the plasma and how these fields are set up and powered?

As the ions in the plasma are charged (the plasma is so hot all the electrons are stripped off the atoms, leaving them with a positive charge) they respond to magnetic fields. By setting up magnetic field lines toroidally around the interior of the tokamak, the ions and electrons in […]

How much electricity has been consumed by JET to this point?

I cannot put a number on the amount of electricity consumed by JET I am afraid, although, suffice to say it is a lot!! Each JET pulse uses ~700MW of electricity (used to directly heat the plasma and also to provide the magnetic fields required to keep the plasma confined).

I’ve read that 10 MW of power could be sustained for only .5 seconds. What is the limitation preventing a longer maintaining of power, and how does the output of power compare to the amount of power invested necessary to produce the 10MW?

In fusion power demonstrations there are usually two different goals. One is to produce a steady, sustainable level of power, the other is to reach as high a power as possible, even if this is only possible for a short time. In the 1997 JET experiments, for instance, a steady […]

How long is the longest sustained fusion reaction achieved by JET and elsewhere?

Most of the experiments that are carried out in fusion research use only deuterium, rather than a combination of deuterium and tritium (D-T). This is because tritium, as a radioactive gas, is more expensive and has significantly more complicated handling requirements than deuterium. Deuterium-only plasma is sufficient for most of […]

What is plasma current and what is a JET pulse?

Plasma current is the flow of charged particles around the tokamak’s donut-shaped vessel (as opposed to the random movement of the hot plasma particles). It is induced in the same way that a transformer works. The primary coil is a large electromagnetic coil in the centre of the donut (its […]

Where is the JET Tokamak located?

The JET machine is at the Culham Science Centre near Abingdon, about 9 miles south from Oxford in the UK.

What output fusion power has been achieved by JET and for what containment time?

Most of JET’s experimental campaigns use deuterium only plasma; deuterium is almost identical to tritium and so the plasma is very similar and is perfect for researching the behaviour and stability of fusion experiments, without the expense and complications of handling tritium, which is radioactive. We have however run three […]

I am wondering how fusion reactions can reach their break even points. How does fusion manage to release energy out of nowhere? I know it’s not out of nowhere since energy doesn’t work that way, but where does it come from?

In fusion, energy is released when deuterium and tritium nuclei fuse together to make a helium nucleus and a neutron.  This energy release is all to do with something called binding energy – the fundamental energy which binds any nucleus together.  Essentially the deuterium and tritium nuclei require more binding […]





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