US Scientists Develop an Innovative Magnet to Increase Efficiency of Nuclear Power Plants

A tokamak is a machine used to enclose plasma through doughnut shape magnetic fields called a torus. Plasma is a superheated matter that contains a large amount of charged particles such as ions, atomic nuclei and free electrons. It undergoes nuclear fusion to generate energy. Nuclear fusion is a reaction in which two or more atomic nuclei combine to form two or more subatomic particles (protons and neutrons) or atomic nuclei. Examples of plasma include natural phenomena such as lightning, aurorae, solar storm, star lightning.

In a tokamak, electric and magnetic fields are generated by a central electromagnet called Solenoid. It creates a twisted movement of electric and magnetic fields to confine the plasma. After being exposed to the plasma’s subatomic particles, neutrons, the insulating wire across the electromagnet (Solenoid) degrades. This reduces the efficiency of tokamak to generate nuclear fusion energy.

The PPPL developed magnet contains metal that acts as insulation and prevents the electromagnet from damaging. It can be used at higher temperatures than present superconducting electromagnets and is easily maintained. Further, scientists are seeking to use nuclear fusion to generate inexhaustible electric energy.

“Our innovation both simplifies the fabrication process and makes the magnet more tolerant of the radiation produced by the fusion reactions,” said Yuhu Zhai, an engineer at PPPL and lead author of the study.

“If we are designing a power plant that will run continuously for hours or days, then we can’t use current magnets,” said Zhai. “Those facilities will produce more high-energy particles than current experimental facilities do. The magnets in production today would not last long enough for future facilities like commercial fusion power plants.”

Electromagnets are different from simple permanent magnets. They contain electric current carrying insulated wire that generates a magnetic field as the current flows. They are used in several devices, including tokamaks, cranes, MRI machines, etc.

Zhai and his team have built a prototype magnet and got positive results. “During our tests, our magnet produced about 83 percent of the maximum amount of electrical current the wires can carry, a very good amount,” he said. “Scientists typically only use 70 percent of the superconducting wire electrical current capacity when designing and building high-power magnets. And large-scale magnets like those used in ITER, the international fusion facility being constructed in France, often use only 50 percent.”

The new magnets have wires of metals such as niobium and tin. When the wires are heated, these elements become superconductors and allow the electric current to pass through them at low temperatures with no resistance. Hence, the need for insulation decreases to prevent current leakage.

“This new concept is interesting because it allows the magnet to carry a lot of electrical current in a little space, reducing the amount of volume the magnet occupies in a tokamak,” said Robert Ellis, chief engineer at PPPL. “This magnet could also operate at higher current densities and stronger magnetic fields than magnets can today. Both qualities are important and could lead to lower costs.”

Overall, the new magnet could help to develop nuclear fusion energy. “This is a revolutionary change in how you make electromagnets,” said Michael Zarnstorff, Chief Science Officer at PPPL. “By creating a magnet with just metal and removing the need to use insulation, you get rid of a lot of costly steps and reduce the number of opportunities for the coil to malfunction. This is really important stuff.”

The study results have been published in the journal Superconductor Science and Technology.

Contributed by: Simran Dolwani