Nuclear fusion how long

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Their idea involves firing a projectile at a target that contains hydrogen atoms. The shockwave from the impact of the projectile creates a shockwave that crushes the fuel and briefly this reaction will produce plasma that is hotter than the sun and denser than lead.

It is focusing on developing a Tokamak system but its key innovation is in superconducting magnets. They hope to build powerful enough magnets so they can build smaller and cheaper Tokomaks to contain the plasmas required to generate fusion. TAE Technologies: With backing from Google and other high tech investors, this California-based company is using a different mix of fuel to develop smaller, cheaper reactors. They want to use hydrogen and boron as both elements are readily available and non-radioactive.

Their prototype is a cylindrical colliding beam fusion reactor CBFR that heats hydrogen gas to form two rings of plasma. These are merged and held together with beams of neutral particles to make it hotter and last longer. US Navy : Worried about how to power their ships in the future, the US Navy has filed a patent for a "plasma compression fusion device".

The idea would be to make fusion power reactors small enough to be portable. There's a lot of scepticism that this approach will work. One of the main challengers with ambitions to make fusion work is a company based in British Columbia, Canada called General Fusion. Their approach, which has gathered a lot of attention and backing from the likes of Amazon's Jeff Bezos, combines cutting edge physics with off the shelf technology.

They call their system "magnetised target fusion". This approach sees a hot gas plasma injected into a ball of liquid metal inside a steel sphere. It is then compressed by pistons, much like in a diesel engine.

General Fusion say they hope to have a working model within five years. Despite the hopes, no one to date has managed to get more energy out of a fusion experiment than they have put in. Most experts are confident the idea will work, but many believe that it is a matter of scale. To make it work, you have to go large. 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.

A range of MTF systems are currently being experimented with, and commonly use a magnetic field to confine a plasma with compressional heating provided by laser, electromagnetic or mechanical liner implosion.

As a result of this combined approach, shorter plasma confinement times are required than for magnetic confinement from ns to 1 ms, depending on the MIF approach , reducing the requirement to stabilize the plasma for long periods. Conversely, compression can be achieved over timescales longer than those typical for inertial confinement, making it possible to achieve compression through mechanical, magnetic, chemical, or relatively low-powered laser drivers.

Due to the reduced demands on confinement time and compression velocities, MTF has been pursued as a lower-cost and simpler approach to investigating these challenges than conventional fusion projects.

Fusion can also be combined with fission in what is referred to as hybrid nuclear fusion where the blanket surrounding the core is a subcritical fission reactor. The fusion reaction acts as a source of neutrons for the surrounding blanket, where these neutrons are captured, resulting in fission reactions taking place.

This confinement time needs to be long enough to allow sufficient plasma energy to circulate in the confined region so that confined ions are kept hot enough to maintain an appropriate level of fusion. Current devices have managed confinement times of about 0. Recent studies have identified confinement quality as the most important factor for reducing capital costs, because it has a direct impact on the necessary size of the tokamak as well as other critical elements of the plant, such as the handling of heat and particle loads.

Further research is necessary to develop higher-quality confinement solutions that would reduce these costs. Though high-temperature superconducting materials, which can generate much stronger magnetic fields, have created some excitement in the fusion community, it is not yet known how well these will perform in operation, and studies have suggested that the choice of magnet technology may have relatively little impact on cost-effectiveness. Tokamak Materials. The neutron radiation produced by DT fusion is an order of magnitude more energetic than that produced by nuclear fission.

In addition, the helium generated by the reaction, as well as excess heat and other impurities in the plasma, must be removed on an ongoing basis during operation.

This exhaust path will be subject to extremely high temperatures and particle bombardment. No materials currently exist that can be confidently relied upon to survive these conditions over the life of a commercial power plant.

Developing them is an active area of research, with work exploring new alloys, better materials, and even liquid surfaces and candidate solutions.

Better understanding of how these materials behave in the reactor environment and their interaction with fusion performance is necessary. Breeding Tritium. Deuterium is relatively abundant in nature, and sufficient supplies can be extracted from seawater. Tritium, however, is a radioactive isotope with a half-life of only Though it exists naturally, it is far too rare to recover usefully from natural sources, and useable amounts must be manufactured.

Current methods rely on extraction from the coolant in heavy-water reactors or bombardment of lithium targets in light-water reactors. A single MW fusion power plant is expected to require about 50 kilograms kg of tritium fuel per year.

Thus, fusion power plants will need a method to breed tritium in situ. Fortunately, the fusion reaction itself offers a potential means to do so. Placing a lithium blanket around the tokamak would generate tritium and further heat as the fusion neutrons are captured by the lithium nuclei and spontaneously transition to tritium. Technology solutions to capture this tritium during operation are in development. Power Generation. To be useful as a power plant, a fusion reactor obviously must generate electricity.

Fusion researchers generally envision that heat from the tokamak will be used to drive turbine generators, but exactly how the heat off-take will function is still a matter requiring considerable engineering. While in a sense this is the most conventional part of the power plant design, the technological challenges remain significant, as for high efficiency, the device must operate at high temperatures. Most current designs envision a helium loop that would extract heat from the lithium blanket, and either drive a turbine directly or generate steam in a secondary loop.

Fusion scientists realized some time ago that existing tokamaks are simply not large or powerful enough to reach burning plasma conditions. In order to resolve the design of a power plant, research at power-plant scale is necessary. Thus, a long-term goal has been building a facility that would have the necessary capabilities. Under the agreement, all members have equal access to the technology developed, though each member funds only a portion of the cost.

The U. Although initial work began in , it took until before an engineering design was agreed upon. This brought the coalition to seven groups comprising 35 nations, making ITER the largest multinational science project in history. The current ITER agreement was signed in , and a location near Aix-en-Provence in southern France was selected as the site of the facility.

However, there were considerable challenges in getting such a large project with so many members off the ground. Construction proceeded somewhat fitfully for several years and fell badly behind schedule. The delays and budget overruns drew concern from several quarters, particularly the appropriations committees in Congress. This February fish-eye view above the ITER tokamak chamber under construction gives an idea of the impressive scale of the device. When complete, the tokamak will be nearly 13 meters across.

In , Bernard Bigot, the former director of the French Atomic Energy Commission, was brought in to assume oversight of the project. Bigot was successful in establishing a professional project culture, and construction is now two-thirds complete. ITER will have many capabilities that go well beyond current tokamaks. It will be the first device that can generate a burning plasma and explore the fundamentals of how a tokamak contains the fusion reaction and the process of self-heating.

This cutaway schematic of the ITER facility shows the tokamak in the center with a simulation of the fusion plasma inside the tokamak. The entire device is about five stories tall.