The plasma used in fusion reactors holds great potential in terms of bringing down costs of this energy source. Over the past few years, researchers have been exploring ways to contain and stabilize this plasma.
During the International Atomic Energy Association’s 24th annual Fusion Energy Conference, held in San Diego this week, the team led by Thomas Jarboe, Proffesor of aeronautics and astronautics at University of Washington, presented a method that uses around 1% of the energy required by existing methods, to contain the material.
The shape of the new tool resembles a handles on a coffee mug. It is attached to a vessel filled with plasma heated to 1 million degrees. The process of nuclear fission, where nuclear power is generated from splitting of an atom, is known to many, however nuclear fusion, where two atoms are smashed together, is still under research. It is established that during this process, energy is released without generating radioactive waste, or using rare elements.
Most people know about nuclear fission, the commercial type of nuclear power generated from splitting large atoms in two. Still under research is nuclear fusion, which smashes two small atoms together, releasing energy without requiring rare elements or generating radioactive waste.
The main limitation of this process is the amount of energy needed in order to bring the atoms together. The focus of current studies is directed towards finding a way to produce more energy that the amount put in.
Jarboe commented on the method used in a big international project, based in France, where the teams are constructing a huge fusion reactor in order to generate fusion power. This reactor is designed to inject high-frequency electromagnetic waves, together with high-speed hydrogen ions to sustain the plasma. These two components should keep the operation temperature at a million degrees and enclose it with magnetic fields.
According to the Professor from Washington University, however, the method is inefficient and too expensive. Therefore, together with his team, he has worked on finding better alternatives. They have investigated helicity injection, where spirals in the plasma produce asymmetric currents. These produce electric and magnetic fields that do similar job in heating and preserving the contents.
The high temperature of the plasma causes electrons to separate from the nuclei and keep it away from any contact with the walls, allowing it to be contained by a magnetic bottle.
The team found that although the required input energy is still high, it is a lot less than what is used in other existing methods. The system, however, was still vulnerable and any small twist in the plasma could disturb the equilibrium of the system and shutdown the reactor.
This presented a major challenge. The team’s initial concern was leakage during a distortion of the bottle. They wanted to stabilize the equilibrium, so small shifts would go back to their original state. To do this, they imposed the asymmetric field, which stabilized the plasma and driving of the current was possible, allowing the bottle to hold more plasma.
The equipment that they developed has two coils in the shape of handles. They follow the so-called method of imposed dynamo current drive, where the “handles” generate currents on either side of the central core alternately. The plasma remains stable, the method is energy-efficient, however the reactor used in their study is too small to contain all plasma and gas still manages to escape. Whether a larger reactor would be able to maintain a sufficiently tight magnetic bottle, we will find out from the team’s next publication.