He said the organization does not believe there is any public misunderstanding of the Q ratio, nor does it believe its representation of Q was vague or incorrect. Coblentz said that ITER has made efforts in the past to reach out to publications and journalists when it felt the Q ratio was misrepresented, and that despite simplifications made by congressional representatives during hearings, ITER is confident lawmakers correctly understand the goals of the project.
In the meantime, Steven Krivit has reached out to the organizations who had published the Q ratio without an explanation of what it meant. Go on an adventure into unexpected corners of the health and science world each week with award-winning host Maiken Scott.
Exploring the space-time-stench continuum, where no nose has gone before. Why NASA is creating — and then sniffing out — some of the foulest smells known in the universe. For decades, slavery created challenges for Black Americans trying to trace their roots. DNA ancestry tests might reveal new answers. Sign up for our weekly newsletter. Skip to content Science Energy Technology. Those latter ingredients, he added, can be harder to come by. But Krivit is skeptical. What did all that mean for ITER, and its claim to be able to produce 10 times the power it used?
Subscribe to The Pulse Stories about the people and places at the heart of health and science. Ways to Listen. Will ITER actually produce 10 times more energy than it consumes? Mark Henderson said the answer depends on what you mean by energy. According to Henderson, physicists and non-physicists think of Q differently. Share this Facebook Twitter Email. Brought to you by The Pulse. The Pulse Go on an adventure into unexpected corners of the health and science world each week with award-winning host Maiken Scott.
More segments from The Magic of Energy Listen. You may also like. However, the challenges involved in handling radioactive tritium and dealing with the copious amounts of energy and fusion products produced, means most present fusion experiments study the fusion of deuterium to deuterium which has a lower fusion reaction rate and then extrapolate the results to DT. DT fusion produces an extremely energetic The reaction also generates a helium nucleus that carries away about one-fifth of the reaction energy 3.
In a fusion reactor, this nucleus shares its energy with the surrounding ions, keeping them hot and sustaining the fusion process.
Though there are a number of methods by which fusion can be induced, consensus research into practical fusion energy has settled on magnetic confinement as the most promising for electricity generation. Most fusion research employs a magnetic confinement device known as a tokamak. First developed by Russian physicists Andrei Sakharov and Igor Tamm during the s, a tokamak is a toroidal that is, torus- or donut-shaped vacuum vessel that uses powerful electromagnets to confine and shape the plasma.
A tokamak consists of a vacuum chamber surrounded by an array of electromagnetic coils that work together to confine the plasma inside strong magnetic fields left. Courtesy: General Atomics. Creating and maintaining the confining magnetic fields in a tokamak requires three arrays of magnets Figure 3. External coils around the ring of the tokamak produce the toroidal magnetic field, parallel to the circumference of the torus.
The central solenoid uses a powerful pulse of energy that generates a toroidal current within the plasma. The movement of ions with this current in turn creates a second poloidal parallel to the poles magnetic field. Finally, poloidal coils around the circumference of the torus are used to control the position and shape of the plasma. Rather than a single magnetic field, the arrangement results in an array of nested flux surfaces that confine the ionized particles in a variety of orbits in and around the tokamak.
Because the particles in the plasma are tied to the magnetic fields, this field structure keeps the hottest parts of the plasma away from the walls, creating an insulating effect that allows very high temperatures to be achieved. The induced plasma current provides a critical element of the magnetic confinement as well as a certain amount of heating, but this alone is not enough to induce fusion.
Additional heating is typically provided by microwaves and particle beams. Several dozen tokamaks are now in operation around the world. A similar device in Japan is being upgraded to study techniques for future facilities and plasma sustainment. Some fusion research employs a device similar to a tokamak known as a stellarator. Rather than having a large plasma current, a stellarator uses a twisted array of helical windings around the torus to create the poloidal field externally.
As a result, it does not need to generate a plasma current, which means it is capable of steady-state operation rather than needing a pulse of energy from the central solenoid. However, stellarators have more complicated geometry and are more difficult to build because of these additional windings.
The approach is thought to offer considerable promise, and though past stellarators have encountered more problems with plasma confinement than tokamaks, the technology continues to draw research attention. The Wendelstein 7-X, an advanced stellarator that went online in Germany in also the largest so far is studying how well stellarators can contain energy and reach fusion conditions.
No current device has been able to generate more fusion power than the heating energy required to start the reaction. Scientists measure this assessment with a value known as fusion gain expressed as the symbol Q , which is the ratio of fusion power to the input power required to maintain the reaction.
Fusion power plants will need to achieve Q values well above 10 to be economic. The many potential benefits of fusion as an energy source are the reason it has long been viewed as an ideal method of generation. The fuel—isotopes of hydrogen—is readily available, and the only by-product is helium. Like a gas, coal, or fission plant, a fusion plant could operate around the clock, yet without producing any harmful emissions or long-lived radioisotopes. The risk of accidents with a fusion plant is very limited—if containment is lost, the fusion reaction simply stops.
Though fusion is not risk-free, no explosions or wide-scale releases of energy are possible. Getting to practical generation has been the key challenge. After more than 60 years of research in magnetic confinement fusion, most of the remaining impediments to fusion energy are those of engineering rather than science, though there are still important physics questions being investigated.
Plasma Confinement. Confining a fusion plasma inside a magnetic field is a bit like squeezing water inside a balloon. Differences in pressure, temperature, and density can cause the fields to balloon outward or spring a leak.
Researchers have been able to confine fusion plasmas long enough to generate fusion reactions for many years. However, the quality of plasma confinement—defined as the time required to lose energy to the vessel walls—is a key element in the cost-effectiveness of a hypothetical fusion power plant. 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. The magnetic confinement approach promises better development prospects and is thus the preferred route for energy production so far.
The vast majority of research focuses on tokamaks , fusion reactors invented in the USSR in the s, where the plasma is confined by a strong magnetic field.
ITER , a demonstration reactor under construction in the south of France involving 35 countries, uses the tokamak configuration. The first plasma is now officially expected by the end of , with a demonstration of fusion expected in the late s.
China is also pursuing an ambitious programme to produce tritium isotopes and electricity in the s. Though stellarator performances are lower than what a tokamak can achieve, its intrinsic stability and promising recent results make it a serious alternative.
Meanwhile, private nuclear fusion projects have been booming in recent years. While these initiatives use other innovative technologies to reach fusion and could thus very well deliver operational reactors fast, deploying a fleet of reactors throughout the world is bound to take time. This article was originally published in French. Portsmouth Climate Festival — Portsmouth, Portsmouth. Edition: Available editions United Kingdom.
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