• Exterior view of the Ignitor fusion reactor, whose core will be built in Italy and external housing built outside Moscow, where it will be installed.

    Image courtesy of Bruno Coppi

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  • Internal cutaway view of the reactor, showing the donut-shaped cavity that houses the hot plasma where fusion will take place.

    Image courtesy of Bruno Coppi

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New project aims for fusion ignition

MIT-led Ignitor reactor could be the world’s first to reach major milestone, perhaps paving the way for eventual power production.


Russia and Italy have entered into an agreement to build a new fusion reactor outside Moscow that could become the first such reactor to achieve ignition, the point where a fusion reaction becomes self-sustaining instead of requiring a constant input of energy. The design for the reactor, called Ignitor, originated with MIT physics professor Bruno Coppi, who will be the project’s principal investigator.

The concept for the new reactor builds on decades of experience with MIT’s Alcator fusion research program, also initiated by Coppi, which in its present version (called Alcator C-Mod) has the highest magnetic field and highest plasma pressure (two of the most important measures of performance in magnetic fusion) of any fusion reactor, and is the largest university-based fusion reactor in the world.

The key ingredient in all fusion experiments is plasma, a kind of hot gas made up of charged particles such as atomic nuclei and electrons. In fusion reactors, atomic nuclei — usually of isotopes of hydrogen called deuterium and tritium — are forced together through a combination of heat and pressure to overcome their natural electrostatic repulsion. When the nuclei join together, or fuse, they release prodigious amounts of energy.

Ignitor would be about twice the size of Alcator C-Mod, with a main donut-shaped chamber 1.3 meters across, and have an even stronger magnetic field. It will be much smaller and less expensive than the major international fusion project called ITER (with a chamber 6.2 meters across), currently under construction in France. Though originally designed to achieve ignition, the ITER reactor has been scaled back and is now not expected to reach that milestone.

The Ignitor reactor, Coppi says, will be “a very compact, inexpensive type of machine,” and unlike the larger ITER could be ready to begin operations within a few years. Its design is based on a particularly effective combination of factors that researchers  unexpectedly discovered during the many years of running the Alcator program, and that were later confirmed in experiments at other reactors. Together, these factors produce especially good confinement of the plasma and a high degree of purity (impurities in the hot gases can be a major source of inefficiency). The new design aims to preserve these features to produce the highest plasma current densities — the amount of electric current in a given area of plasma. The design also has additional structures needed to produce and confine burning fusion plasmas in order to create the conditions needed for ignition, Coppi says.

A project at Lawrence Livermore National Laboratory in California, called the National Ignition Facility, uses a completely different approach to fusion, bombarding a tiny pellet of fuel with laser beams to create the heat and pressure needed for fusion. But some physicists disagree on the exact meaning of fusion ignition, and whether the results of the planned experiments at NIF can truly be considered ignition. ”I don’t understand how they define ignition,” Coppi says of what is being planned at NIF.

Coppi plans to work with the Italian ministry of research and Evgeny Velikhov, president of the Kurchatov Institute in Moscow, to finalize the distribution of tasks for the machine, the core of which is to be built in Italy and then installed in Troitsk, near Moscow, on the site of that institute’s present Triniti reactor. Velikhov, as it happens, is also the chair of the ITER council. Coppi says of these two different programs,  “there’s no competition, we are complementary.”

Although seen as a possible significant contributor to the world’s energy needs because it would be free of greenhouse-gas emissions, practical fusion power remains at least two decades away, most scientists in the field agree. But the initial impetus for setting up the Alcator reactor in the 1970s had more to do with pure science: “It was set up to simulate the X-ray stars that we knew at that time,” says Coppi, whose research work has as much to do with astrophysics as with energy. Stars are themselves made of plasma and powered by fusion, and the only way to study their atomic-level behavior in detail is through experiments inside fusion reactors.

Once the reactor was in operation, he says, “we found we were producing plasmas with unusual properties,” and realized this might represent a path to the long-sought goal of fusion ignition.

Roscoe White, a distinguished research fellow at the Princeton Plasma Physics Laboratory, says that “the whole point of Ignitor is to find out how a burning plasma behaves, and there could be pleasant or unpleasant results coming from it. Whatever is learned is a gain.  Nobody knows exactly how it will perform, that is the point of the experiment.” But while its exact results are unknown, White says it is important to pursue this project in addition to other approaches to fusion. “With our present knowledge it is very risky to commit the program to a single track reactor development — our knowledge is still in flux,” he says.

In addition, he says, “the completion of ITER, the only currently projected burning plasma experiment, is decades off. Experimental data concerning a burning plasma would be very welcome, and could lead to important results helping the cause of practical fusion power.” Furthermore, the Ignitor approach, if all goes well, could lead to more compact and economical future reactors: Some recent results from existing reactors, plus new information to be gained from Ignitor, “could lead to reactor designs much smaller and simpler than ITER,” he says.

Coppi remains especially interested in the potential of the new reactor to make new discoveries about fundamental physics. Quoting the late MIT physicist and Institute Professor Bruno Rossi, Coppi says, “whenever you do experiments in an unknown regime, you will find something new.” The new machine’s findings, he suggests, “will have a strong impact on astrophysics.”


Topics: Energy, Fusion, Nuclear science and engineering, Physics, Plasma, Plasma Science and Fusion Center

Comments

I applaud the decision to finally build Ignitor, and lots of very important science will come out of the device for the magnetic confinement fusion community. However the article is misleading in stating that Ignitor will be the first device to achieve fusion ignition. The National Ignition Facility (NIF) at Lawrence Livermore National Lab in California is currently gearing up for ignition experiments in inertial confinement fusion. We expect the NIF to demonstrate the first ignited laboratory plasma in the next 1-2 years. Ignitor may well be the first tokamak to demonstrate ignition; but ignition will most likely have been achieved at NIF before Ignitor is first turned on. <strong><em>Editor's note:</em> In response to this comment, the following paragraph has been added to the story: A project at Lawrence Livermore National Laboratory in California, called the National Ignition Facility, uses a completely different approach to fusion, bombarding a tiny pellet of fuel with laser beams to create the heat and pressure needed for fusion. But some physicists disagree on the exact meaning of fusion ignition, and whether the results of the planned experiments at NIF can truly be considered ignition. ”I don’t understand how they define ignition,” Coppi says of what is being planned at NIF.</strong>
This is a great milestone, hope everything goes well!
While this is a good article, I also disagree with the statement: Though originally designed to achieve ignition, the ITER reactor has been scaled back and is now not expected to reach that milestone. Not because it is technically wrong, but it spreads confusion. Ignition is defined to be, " [when] the applied heating can then be removed and the plasma temperature is sustained by internal heating." from Tokamaks (Wesson, 10) In the plasma physics world we care about Q: the ratio of the thermonuclear power to the applied power. ITER is expected to reach a Q of 10, so 10 times more power out than we put in. It is undesirable from an engineering point of view to not put any power into the reactor because then you will lose control of it. Wesson explains this sentiment well, "It is seen that although an ignited plasma has the desirable feature that no applied heating is required, it is quite possible to obtain a large Q without ignition" (12) A fusion reactor, such as DEMO, will likely have a Q of 30 to 40.
It would be good to put sizing information into the picture, for width, height, etc.
The ALCATOR mentioned in the article stands for Alto Campo Torus - high field torus. Built on the principle that high plasma pressure, not large plasma size, was the route to long plasma confinement time, each of the ALCATOR tokamaks set world records for plasma confinement. As the scaled up successor to the venerable ALCATOR Tokamak line, I have no doubt that Ignitor will continue the ALCATOR tradition. On a personal note, when I was a grad student at ALCATOR A and C in the 80s, Bruno Coppi was a droll, colorful, and brilliant fellow. (The Russians dont know what they're getting into.) It's great to see that Bruno is still pushing the envelope!
In the cutaway drawing, the vacuum chamber major radius is 132 cm (i.e., from the donut centerline to the center of the D-shaped vacuum chamber). In the external drawing, a six foot (183 cm) tall grad student would almost be able to stand up straight under the machine.
In response to Professor Coppi's comment about ignition at NIF: The definition of ignition in an inertial confinement fusion facility such as NIF is straightforward: "ignition is defined as the ratio of fusion energy released to laser energy absorbed in the hohlraum" (from "Plasma Science: Advancing Knowledge in the National Interest" :Plasma 2010 Committee, Plasma Science Committee,National Research Council). In the early ignition campaigns planned for NIF in 2011-2012, NIF will generate roughly 10 to 20 times more energy than the laser energy delivered on the target – the scientific definition of ignition and net fusion target energy gain – not the wallplug energy required to power the lasers. NIF’s goal is to demonstrate the physics of laser-driven inertial confinement fusion; the next generation of ICF facilities, such as the Laser Inertial Fusion Energy (LIFE) engine now being designed at Lawrence Livermore National Laboratory, will be designed to generate net energy.
I was an undergradute when Alcator was built and I was there for the early experiments The earliest purpose of Alcator was to study heating of very low density plasma where the heating was enhanced over Ohmic heating At the time everyone building a Tokamak had to have a gimic to get funded. Alcator's was high fields which could permit very high current density -- it was assumed that this high current concentrated in a small cross section would lead to strong Ohmic heating in plasmas with typical (for the time electron density) -- it didn't The next idea was to lower the electron densiy and then depend on a form of turbulent heating -- due to slide-away electrons in the tail of the electron distribution interacting with the bulk and creating "catalytic resistivity" We made slide-away electrons and a lot of x-rays but there was no significant heating Alcator finally started to make progress after its first rebuild when the idea was to bost the density through puffing extra hydrogen. It worked and the era of high density in Alcator and the overall CTR Tokamak comunity began. Later came Miklos POorkolab and electron and ion cyclotron resonance heating. Still later the whole C-Mod, etc. I would give Bruno, Ben Lax and several others the credit for the original Alcator based on the Francis Bitter National Magnet Lab's expertise with Bitter Magnets and the availability of the original High Current Motor-Generator Power Supply. Note however that the original low density stuff -- which didn't wok -- was due to Bruno's theoretical work. What actually worked (i.e. high density plasma with high plasma currents and external heating souces) and which ultimately led to the current Alcator C-Mod was essentially the antithesis of Bruno's ideas for operation of Alcator.
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