How does nuclear fusion work

This was a joint effort between fusion science researchers from the United States, Soviet Union, European Union, and Japan, as fusion energy researchers had quickly discovered that no one nation had the resources to develop a powerful enough tokamak fusion reactor on their own.

JET is one of the only facilities in the world that makes more neutrons than us! Currently, while advances in plasma science and materials science are still needed to make fusion reactors that can output more fusion energy than it takes in, tokamak reactors are still regarded as the most promising path in fusion research to one day creating power plants for clean fusion energy production.

Inertial confinement fusion relies on shooting high-energy laser beams at a fuel pellet target containing deuterium and tritium fuel for the reaction. The impact of the high-energy beam causes shockwaves to travel through the fuel pellet target, heating and compressing it to induce fusion reactions.

This method of inducing nuclear fusion reactions was first suggested in the s, and in the s, high-energy ICF inertial confinement fusion research suggested that it could be a more promising path to fusion energy than tokamak and stellarator fusion reactors.

However, over the next two decades, researchers gradually discovered more and more hurdles that needed to be overcome in order to reach ignition within such a fusion reactor, and estimations regarding how much energy the laser beams needed to induce fusion doubled on a yearly basis. Completed in , as of this system has only been able to reach one-third of the conditions needed for ignition. The NIF is currently used mainly for materials science and weapon research rather than fusion power research.

There are also fusion research facilities exploring fusion projects such as colliding beam fusion, which involves accelerating a beam of ions into a stationary target or another beam to induce a nuclear fusion reaction, similar to inertial confinement fusion.

Neutron radiation is a byproduct of all nuclear processes, including fission and fusion, and since the s, industrial and research applications such as neutron radiography and medical isotope production have depended on fission reactors for their high neutron yield. But recent developments in colliding beam fusion, or accelerator fusion, is making fusion a more convenient way to produce neutrons than fission.

On the largest scale of colliding beam fusion are enormous particle accelerators such as the Spallation Neutron Source at Oak Ridge National Laboratory, which produce massive neutron yields and are primarily used for neutron scattering research.

Scientists use neutron scattering to better understand the molecular composition of materials such as metals, polymers, biological samples, and superconductors. On the smallest scale of colliding beam fusion are sealed-tube neutron sources, which are very small accelerators—small enough to fit on a table or workbench, and often small enough to be used for fieldwork—that work by shooting a beam of deuterium or tritium ions at a deuterium or tritium target to make fusion start.

The smaller the neutron source, the lower its yield, and these tiny sealed-tube sources tend to be used mostly for work which only needs a low neutron yield from a portable source, such as oil well logging, coal analysis, and most applications of neutron activation analysis. These sealed-tube sources are widely used in the petroleum industry. These high-flux neutron generators work under the same basic principles as sealed-tube sources, except massively scaled up from tabletop-sized neutron emitters so that they can be used in the same high-yield industrial and research niches as fission reactors.

To make fusion power a reality, we need stronger materials to use in a fusion system and reactor, such as superconducting magnets and shielding material that can withstand the intense operating conditions, and through techniques such as neutron scattering and radiation hardening , we can further fusion research to design and develop the reactor for the fusion power plant of tomorrow. Phoenix, LLC. All Rights Reserved.

Hit enter to search or ESC to close. The Physics of a Nuclear Fusion Reaction Nuclear fusion is one of the simplest, and yet most powerful, physical processes in the universe. Nuclear Fusion in the Sun In the sun, the nuclear fusion process occurs mainly between hydrogen and helium, since that is the bulk of its composition. How Do Nuclear Reactors Work? Fusion vs. Use of energy. Energy and the environment. Also in What is energy? Forms of energy Sources of energy Laws of energy.

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Normally, fusion is not possible because the strongly repulsive electrostatic forces between the positively charged nuclei prevent them from getting close enough together to collide and for fusion to occur.

However, if the conditions are such that the nuclei can overcome the electrostatic forces to the extent that they can come within a very close range of each other, then the attractive nuclear force which binds protons and neutrons together in atomic nuclei between the nuclei will outweigh the repulsive electrostatic force, allowing the nuclei to fuse together. Such conditions can occur when the temperature increases, causing the ions to move faster and eventually reach speeds high enough to bring the ions close enough together.

The nuclei can then fuse, causing a release of energy. In the Sun, massive gravitational forces create the right conditions for fusion, but on Earth they are much harder to achieve.

Fusion fuel — different isotopes of hydrogen — must be heated to extreme temperatures of the order of 50 million degrees Celsius, and must be kept stable under intense pressure, hence dense enough and confined for long enough to allow the nuclei to fuse.

The aim of the controlled fusion research program is to achieve 'ignition', which occurs when enough fusion reactions take place for the process to become self-sustaining, with fresh fuel then being added to continue it. Once ignition is achieved, there is net energy yield — about four times as much as with nuclear fission.

According to the Massachusetts Institute of Technology MIT , the amount of power produced increases with the square of the pressure, so doubling the pressure leads to a fourfold increase in energy production. With current technology, the reaction most readily feasible is between the nuclei of the two heavy forms isotopes of hydrogen — deuterium D and tritium T. Each D-T fusion event releases Deuterium occurs naturally in seawater 30 grams per cubic metre , which makes it very abundant relative to other energy resources.

Tritium occurs naturally only in trace quantities produced by cosmic rays and is radioactive, with a half-life of around 12 years. Usable quantities can be made in a conventional nuclear reactor, or in the present context, bred in a fusion system from lithium. In a fusion reactor, the concept is that neutrons generated from the D-T fusion reaction will be absorbed in a blanket containing lithium which surrounds the core.

The lithium is then transformed into tritium which is used to fuel the reactor and helium. The blanket must be thick enough about 1 metre to slow down the high-energy 14 MeV neutrons. The kinetic energy of the neutrons is absorbed by the blanket, causing it to heat up. The heat energy is collected by the coolant water, helium or Li-Pb eutectic flowing through the blanket and, in a fusion power plant, this energy will be used to generate electricity by conventional methods.

If insufficient tritium is produced, some supplementary source must be employed such as using a fission reactor to irradiate heavy water or lithium with neutrons, and extraneous tritium creates difficulties with handling, storage and transport. The difficulty has been to develop a device that can heat the D-T fuel to a high enough temperature and confine it long enough so that more energy is released through fusion reactions than is used to get the reaction going.

While the D-T reaction is the main focus of attention, long-term hopes are for a D-D reaction, but this requires much higher temperatures. In any case, the challenge is to apply the heat to human needs, primarily generating electricity. The energy density of fusion reactions in gas is very much less than for fission reactions in solid fuel, and as noted the heat yield per reaction is 70 times less.

Hence thermonuclear fusion will always have a much lower power density than nuclear fission, which means that any fusion reactor needs to be larger and therefore more costly, than a fission reactor of the same power output.

In addition, nuclear fission reactors use solid fuel which is denser than a thermonuclear plasma, so the energy released is more concentrated. Also the neutron energy from fusion is higher than from fission — At present, two main experimental approaches are being studied: magnetic confinement and inertial confinement.

The first method uses strong magnetic fields to contain the hot plasma. The second involves compressing a small pellet containing fusion fuel to extremely high densities using strong lasers or particle beams. In magnetic confinement fusion MCF , hundreds of cubic metres of D-T plasma at a density of less than a milligram per cubic metre are confined by a magnetic field at a few atmospheres pressure and heated to fusion temperature.

Magnetic fields are ideal for confining a plasma because the electrical charges on the separated ions and electrons mean that they follow the magnetic field lines.

The aim is to prevent the particles from coming into contact with the reactor walls as this will dissipate their heat and slow them down. The most effective magnetic configuration is toroidal, shaped like a doughnut, in which the magnetic field is curved around to form a closed loop. For proper confinement, this toroidal field must have superimposed upon it a perpendicular field component a poloidal field.

The result is a magnetic field with force lines following spiral helical paths that confine and control the plasma. There are several types of toroidal confinement system, the most important being tokamaks, stellarators and reversed field pinch RFP devices.

In a tokamak, the toroidal field is created by a series of coils evenly spaced around the torus-shaped reactor, and the poloidal field is created by a system of horizontal coils outside the toroidal magnet structure. A strong electric current is induced in the plasma using a central solenoid, and this induced current also contributes to the poloidal field.

In a stellarator, the helical lines of force are produced by a series of coils which may themselves be helical in shape. Unlike tokamaks, stellarators do not require a toroidal current to be induced in the plasma. RFP devices have the same toroidal and poloidal components as a tokamak, but the current flowing through the plasma is much stronger and the direction of the toroidal field within the plasma is reversed. In tokamaks and RFP devices, the current flowing through the plasma also serves to heat it to a temperature of about 10 million degrees Celsius.

Beyond that, additional heating systems are needed to achieve the temperatures necessary for fusion. In stellarators, these heating systems have to supply all the energy needed. The tokamak toroidalnya kamera ee magnetnaya katushka — torus-shaped magnetic chamber was designed in by Soviet physicists Andrei Sakharov and Igor Tamm.

Tokamaks operate within limited parameters outside which sudden losses of energy confinement disruptions can occur, causing major thermal and mechanical stresses to the structure and walls. Nevertheless, it is considered the most promising design, and research is continuing on various tokamaks around the world.

Research is also being carried out on several types of stellarator. Lyman Spitzer devised and began work on the first fusion device — a stellarator — at the Princeton Plasma Physics Laboratory in Due to the difficulty in confining plasmas, stellarators fell out of favour until computer modelling techniques allowed accurate geometries to be calculated.

Because stellarators have no toroidal plasma current, plasma stability is increased compared with tokamaks. Since the burning plasma can be more easily controlled and monitored, stellerators have an intrinsic potential for steady-state, continuous operation. The disadvantage is that, due to their more complex shape, stellarators are much more complex than tokamaks to design and build. RFP devices differ from tokamaks mainly in the spatial distribution of the toroidal magnetic field, which changes sign at the edge of the plasma.

The RFX machine in Padua, Italy is used to study the physical problems arising from the spontaneous reorganisation of the magnetic field, which is an intrinsic feature of this configuration. In inertial confinement fusion, which is a newer line of research, laser or ion beams are focused very precisely onto the surface of a target, which is a pellet of D-T fuel, a few millimetres in diameter.

This heats the outer layer of the material, which explodes outwards generating an inward-moving compression front or implosion that compresses and heats the inner layers of material. The core of the fuel may be compressed to one thousand times its liquid density, resulting in conditions where fusion can occur. The energy released then would heat the surrounding fuel, which may also undergo fusion leading to a chain reaction known as ignition as the reaction spreads outwards through the fuel.

The time required for these reactions to occur is limited by the inertia of the fuel hence the name , but is less than a microsecond. So far, most inertial confinement work has involved lasers. Recent work at Osaka University's Institute of Laser Engineering in Japan suggests that ignition may be achieved at lower temperature with a second very intense laser pulse guided through a millimetre-high gold cone into the compressed fuel, and timed to coincide with the peak compression.

This technique, known as 'fast ignition', means that fuel compression is separated from hot spot generation with ignition, making the process more practical.

In the UK First Light Fusion based near Oxford is researching inertial fusion energy IFE with a focus on power driver technology using an asymmetric implosion approach. As well as power generation, the company envisages material processing and chemical manufacturing applications. It focuses powerful laser beams into a small target in a few billionths of a second, delivering more than 2 MJ of ultraviolet energy and TW of peak power.

A completely different concept, the 'Z-pinch' or 'zeta pinch' , uses a strong electrical current in a plasma to generate X-rays, which compress a tiny D-T fuel cylinder. Magnetized target fusion MTF , also referred to as magneto-inertial fusion MIF , is a pulsed approach to fusion that combines the compressional heating of inertial confinement fusion with the magnetically reduced thermal transport and magnetically enhanced alpha heating of magnetic confinement fusion.

Conceptually, harnessing nuclear fusion in a reactor is a no-brainer. But it has been extremely difficult for scientists to come up with a controllable, nondestructive way of doing it.

To understand why, we need to look at the necessary conditions for nuclear fusion. Isotopes are atoms of the same element that have the same number of protons and electrons but a different number of neutrons. Some common isotopes in fusion are:. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Prev NEXT.