Fusion magnets could lead to improved microchip production

Written by
Raphael Rosen
Nov. 13, 2023

Swooping magnetic fields that confine plasma in doughnut-shaped fusion facilities known as tokamaks could help improve the efficiency of complex machines that produce microchips. This innovation could lead to more powerful computers and smartphones, near-essential devices that make modern society possible.

Engineers use high-energy light emitted by plasma, the electrically charged fourth state of matter, to create small structures on the surfaces of silicon wafers during their transformation into microchips. These tiny components enable a range of devices, including consumer electronics, video games, medical machinery and telecommunications. Improving the generation of this light could extend the life of vital parts within the machines and make the manufacture of microchips more efficient.

“These findings could change the microchip industry,” said Ben Israeli, lead author of the paper publishing the results in Applied Physics Letters. Israeli is a graduate student in the Princeton Program in Plasma Physics, based at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), which Princeton University manages.

Cleaning out the debris

The researchers performed computer simulations showing how to create opposing magnetic fields in chambers holding plasma within the machines that fashion the crucial silicon parts. The magnetic fields push at each other and fan out like river deltas, leaving a central region known as a “magnetic null” that does not experience any magnetic force.

The simulations demonstrate that the outwardly pointing magnetic field lines could carry away unwanted fast plasma particles. If not removed, the particles, called “ions,” could damage the crucial mirror that gathers and focuses the plasma light, and the machine would have to be shut down for extra cleaning.

This technique improves upon other magnetic field configurations that trap the ions but don’t remove them entirely from the surrounding environment. “That’s a problem because when a laser shines into the chamber to ionize the droplets, which are made of tin, there will already be a background plasma composed of trapped ions from previous molten tin droplets ablated by previous laser pulses,” said Marien Simeni, a Richard and Barbara Nelson Assistant Professor of Mechanical Engineering at the University of Minnesota and another member of the team.

ion flight
A computer simulation showing a charged particle moving along magnetic field lines. (Ben Israeli / Princeton Plasma Physics Laboratory)

“Ideally, you want a plasma consisting only of electrons and ions from tin droplets you are currently injecting into the machine, but because of trapped ions from previous sessions, you get an entirely different plasma,” Simeni said. “We don’t have full control over this plasma and don’t yet know the effects of the trapped ions.”

The team plans to study how the magnetic null configuration might interact with a common gas used to fill the chamber during the plasma’s creation. The gas, made of hydrogen molecules, slows the tin plasma particles before they can crash into the mirror and damage it. How background gas might affect the design of the magnetic null configuration and how that configuration might affect the gas remains a mystery.

The power of collaboration

The research shows how collaboration and communication can lead to significant scientific advances. “These results were exciting because they show that to solve complicated problems, it’s good to have people with different scientific backgrounds,” Simeni said. “We used knowledge about plasma in fusion applications to answer questions about a completely different field.”

This research was supported by PPPL’s Laboratory Directed Research and Development (LDRD) program.

PPPL, on Princeton University's Forrestal Campus in Plainsboro, New Jersey, is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. The University manages the Laboratory for the U.S. Department of Energy’s Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science