Fusion is the way the sun and stars produce energy. On the sun, extreme pressure and temperature conditions cause hydrogen atoms to collide and fuse. Here on Earth, we can create the conditions for fusion, in part with magnetic fields.
Electromagnets and superconducting magnets
An electromagnet is a coil of wire wrapped around a mechanical form. When electricity flows through the wire, it creates a magnetic field inside and around the coil. The magnetic field from a single loop of wire is not strong by itself. If the wire is wrapped several times, the strength of the field is multiplied by the number of loops of wire used. Using this technique, very strong magnetic fields can be created inside an electromagnet. In many applications, wires made of a standard metal, like copper, are efficient enough to use. However, a copper coil will have some resistance to the flow of electricity, and it will dissipate energy by heating up. The resistive heating is acceptable if the coil is turned on briefly and then allowed to cool down.
Superconducting magnets are made from special materials like niobium-titanium. These materials have no resistance to electricity when they are kept cold. This allows the coil of wire to carry large electrical currents for a long time without dissipating energy as heat. However, these materials only have superconducting properties at low temperatures – near absolute zero. As a result, superconducting magnets require large and expensive cryogenic cooling systems to operate. In addition, superconductive alloys are more costly to produce and fabricate into wires and coil structures than standard materials like copper.
Why does Magnetized Target Fusion avoid using superconducting magnets?
There are different plasma confinement methods, and General Fusion uses Magnetized Target Fusion (MTF). It is a technology that does not require huge and expensive superconducting magnets used by other fusion technologies. Instead, we use simple electromagnets.
MTF operates on a pulsed basis where fusion conditions are reached briefly but in a repeated cycle. The system relies on the magnetic field to provide thermal confinement during the compression pulse that generates fusion. Because the magnetic field required in MTF is relatively small, we can use readily available copper electromagnets to create the magnetic confinement field. This unique approach also allows our fusion machine to be significantly smaller than other approaches.
General Fusion’s Dr. Stephen Howard talks about how our MTF technology provides a way for several actions required for fusion to all be accomplished by a single physical system: the liquid metal compression system.
A closer look at electromagnets in action in MTF
In MTF, electromagnets are used in the plasma injector that creates a doughnut-shaped plasma. The plasma injector forms a ring of plasma that has a magnetic field embedded within it. Initially, this field is linked back to the electromagnets that created it. The plasma injector also uses a large pulse of current through the plasma that forces the plasma ring forward into the centre of the liquid metal cavity. As it moves forward, it drags the magnetic field forward with it. The plasma and magnetic fields change shape as they disconnect from the field in the injector. This results in a closed doughnut-shaped bubble of plasma with a strong magnetic field wrapping around it and passing through it.
Plasma particles flow along the magnetic field lines, which now circulate without ever touching the wall. In this way, the magnetic field prevents the hot fusion plasma from touching the liquid metal and cooling off. The magnetic field works as an excellent thermal insulator as we heat the core of the plasma, making it hotter than the sun. During the process, the walls of the tank stay cool enough to operate as part of a power plant.
This animation illustrates the effect of electromagnets on plasma in the plasma injector.
How is MTF’s use of magnets different from other fusion concepts?
The integrated design of MTF allows us to use simple and easy to manufacture electromagnets. This is one of the key advantages that keep General Fusion on the fastest path to powering homes, businesses, and industry with clean fusion energy.
