MIT’s experimental fusion reactor, Alcator C-Mod, breaks the plasma pressure record on its last day of operation.

The previous plasma pressure record, 1.77 atmospheres, was set by this same reactor in 2005. Although the reactor has improved the pressure record by nearly 15%, lack of government funding has led to its shutdown.

Before closing down the Tokamak (doughnut-shaped) reactor forever, the MIT team, which had nothing to lose, decided to push the device to its limits. According to Earl Marmar, the team lead, new things were discovered from the experiment without damaging the reactor.

 

Researcher Ted Golfinopoulos performs maintenance in MIT’s Alcator C-Mod. Image courtesy of Computerworld.

 

The record-breaking experiment achieved the plasma pressure of 2.05 atmospheres at 35 million degrees Celsius. Sinking 1.4 million amps, the reactor experienced 300 trillion fusion reactions per second.

Dale Meade, the former deputy director of the Princeton Plasma Physics Laboratory, noted that MIT’s reactor has been highly successful and the new record is quite remarkable. He added that the recent record validates that magnetic confinement would be a good direction to follow for future fusion research.

 

The Challenges of Fusion Energy

Fusion energy is what powers the stars. However, replicating this process on Earth is not easy at all. The principle of fusion energy is that energy and matter are interchangeable and, according to Einstein’s equation, $$E=mc^{2}$$, a tiny bit of matter can produce a vast amount of energy.

There are a number of ways to fuse atoms which cannot be employed in a practical fusion reactor. For example, a fusion bomb is triggered by a small fission bomb; however, this uncontrollable process is not a sustainable option for a fusion reactor.

An alternative method is to use a particle accelerator to fuse individual atoms into one. Unfortunately, this will not produce enough energy for general energy consumption purposes.

Scientists have been experimenting for more than fifty years in attempts to build a practical fusion reactor. And yet, a big payoff does not seem to be achievable for several more decades.

Simply put, a fusion reactor heats atoms to a very high temperature (up to a hundred million degrees) while keeping them contained. Consequently, a state called plasma can be achieved which is a free-flowing mass of protons and electrons.

High temperature, sufficient density, and confinement—as specified by the Lawson criterion—are the key elements of the fusion reaction. Under these conditions, atoms are forced toward each other and, with a mighty release of energy, the two atoms become one. The energy is released in the form of heat and can be used in a way similar to how the heat from fossil fuels is used.

It is necessary to put in some energy to form the plasma and start the reaction. All the modern research reactors have already created fusion. However, there is one major problem: the energy we input to start and keep the reaction going is more than the power we get out of it. How much power does a reactor need? MIT’s experiment consumed a staggering 4 megawatts to initiate the reaction.

A positive energy fusion source requires self-sustaining plasma. In other words, we need the plasma to retain its state by consuming only a small amount of energy. One way to achieve this is by confining the plasma and reaching a certain pressure. According to MIT, pressure is two-thirds of what we need to do to arrive at a practical fusion source. This is mainly due to the fact that the power we get from the reactor increases proportionally with the square of the plasma pressure.

Thanks to its advanced superconductor technology, MIT’s reactor could produce half the power it consumed. Other fusion reactors the same size as the Alcator C-Mod could never come close to producing this much power.

 

The exterior of the Alcator C-Mod. Image courtesy of Computerworld.

 

There are two potential methods to confining the plasma: inertial and magnetic confinement. Here we will have a brief review of these two methods.

 

Inertial Confinement

Inertial confinement fusion is one of the two main potential solutions for building a fusion reactor. This method uses high-energy laser beams to heat the fuel of the nuclear fusion reactions. The heat explodes the outer layer of the fuel, which is a pellet of a few milligrams of Deuterium and Tritium, which accelerates the remainder of the fuel inward. The acceleration and the achieved compression can be strong enough to initiate the fusion reactions.

When the technique was invented in the 1970s, people thought that it would be soon the practical way of achieving fusion power. However, later experiments showed that the power consumed is more than the power achieved. In October 2013, a fusion reactor from the National Ignition Facility could perform a positive-energy experiment.

 

The density and temperature achieved in the inertial confinement implosion can rival those found at the center of the Sun. Image courtesy of Wikipedia.

 

Magnetic Confinement

Plasma is extremely hot and needs to be confined; otherwise, it will rapidly cool down. Due to the very high temperature of the plasma, it is impossible to use any solid material to confine it. To circumvent this problem, researchers use magnetic fields to contain the atoms. Inputting further and further energy in the form of heat, the confined atoms may trigger fusion reactions.

A Tokamak, invented in the 1950s by Soviet physicists, is a fusion reactor which employs two orthogonal magnetic fields to confine the plasma. A Tokamak is based on the conductivity of the plasma and passes a current through it to form a magnetic field called the poloidal field. This field further confines the plasma.

The magnetic confinement seems more promising than the inertial confinement technique, especially after the recent plasma pressure record set by the MIT’s reactor.

 

International Thermonuclear Experimental Reactor (ITER)

The Department of Energy has channeled its financial support to a $30 billion superconducting reactor in France called ITER. This left MIT’s reactor with no further support and shut it down after 23 years of operation.

ITER, which is nearly 800 times larger than MIT’s reactor, is the world’s largest Tokomak with expected heat generation of 500MW. Seven nations, including the U.S., are collaborating to build ITER. ITER’s construction, which is estimated to cost $40 to $50 billion, started in France in 2007 and it will not come online until 2027.

 

An aerial view of ITER. Image courtesy of Computerworld.

 

A fusion reactor can offer a number of advantages over a fission power source. The fuels for the fusion power are the isotopes of hydrogen which are plentiful on the Earth. And the reaction does not produce atmospheric contaminants or long-lived toxic by-products. In addition, the fusion power produces little radioactive waste in comparison with the fission reactors.

 


 

The unlimited clean energy of fusion source must one day be achievable; however, we need to give the researchers enough time and resources. Otherwise, we cannot expect them to work hard and be innovative while being constantly worried about their financial support.

The results of the last experiment of the MIT’s decommissioned reactor were presented at the IAEA’s Fusion Energy Conference in Kyoto on October 17.

 

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