Small shear flow stabilized Z-pinch fusion device sets electronic temperature record

In the nine decades since humans first produced a fusion reaction, only a handful of fusion technologies have demonstrated the ability to create thermal fusion plasmas with electron temperatures above 10 million degrees Celsius, roughly equivalent to the core temperature of the sun. Zap Energy’s unique approach, shear-flow stabilized Z-pinch, has now joined these rarefied ranks by far exceeding this plasma temperature milestone in a device that is only a fraction of the size of other fusion systems.

A new research paper was published in Physical Review Letters, Details of Zap Energy’s Fusion Z-Pinch Experiment (FuZE) measurements of electron temperatures in 1-3 keV plasmas, equivalent to approximately 11 to 37 million degrees Celsius (20 to 66 million degrees Fahrenheit).

This feat is a key hurdle in fusion systems due to the ability of electrons to rapidly cool plasma, and FuZE is the simplest, smallest and cheapest device to achieve this feat. Zap’s technology provides a shorter, more practical path to commercial products capable of producing abundant, on-demand, carbon-free energy for the world.

“These measurements are detailed and well-defined, but were made on a device of extremely limited scale by traditional fusion standards,” said Ben Levitt, vice president of research and development at Zap. “We still have a lot of work to do, but so far our results Performance has advanced to the point where it stands alongside some of the world’s outstanding fusion devices, while being highly efficient and at a fraction of the complexity and cost.”

“In decades of controlled fusion research, only a few fusion concepts have reached the 1 keV electron temperature,” said Scott Hsu, chief fusion coordinator at the U.S. Department of Energy and former ARPA-E project director. “What this team has accomplished here is remarkable and strengthens ARPA-E’s efforts to accelerate the development of commercial fusion energy.”

hot soup

The first step in creating the conditions for fusion is to create plasma—the high-energy “fourth state of matter” in which nuclei and electrons are not bound together to form atoms, but flow freely in a subatomic soup. Compressing and heating a plasma composed of two forms of hydrogen, called deuterium and tritium, causes their nuclei to collide and fuse. When this happens, the fusion reaction releases about 10 million times more energy per ounce than burning the same amount of coal.

This fusion reaction has been observed in relatively small quantities in the laboratory for decades. However, the big challenge is to generate more output fusion energy from these reactions than the input energy required to start them.

Zap Energy’s technology is based on a simple plasma confinement scheme called Z-pinch, in which a large current is directed through a plasma filament. The conductive plasma generates its own electromagnetic field, which heats and compresses it. Although Z-pinch fusion has been experimentally performed since the 1950s, the method has been largely hampered by the short plasma lifetime, which Zap achieved by applying dynamic flow in the plasma, known as shear flow stabilization. process) solved the problem.

“This dynamic is a beautiful balancing act of plasma physics,” Levitt explains. “As we climbed to higher and higher plasma currents, we optimized the sweet spot of temperature, density and lifetime of the Z-pinch to form a stable, high-performance molten plasma.”

healthy pinch

Fusion researchers measure plasma temperature in electron volts and can measure the temperatures of the plasma ions (nuclei) and electrons separately. Because ions are more than a thousand times heavier than electrons, the two components of the plasma can heat and cool at different rates.

Because ions eventually need to be heated to fusion temperatures, plasma physicists often worry about cold electrons limiting ion heating, like ice cubes in hot soup. However, the electrons in the FuZE plasma are as hot as the ions, showing that the plasma is in a healthy thermal equilibrium.

Furthermore, Zap’s detailed measurements showed that electron temperature and fusion neutron production peaked at the same time. Since neutrons are the main product of fusion ions, these observations support the idea that fusion plasmas are in thermal equilibrium.

“The results of this paper and the further tests we have done since then paint a good overall picture of fusion plasmas, with room to expand energy gains,” said Uri Shumlak, co-founder and chief scientist at Zap Energy. “At higher currents Working together, we still see that shear flow extends the Z-pinch lifetime enough to produce the very high temperatures and associated neutron yields we predict through modeling.”

gold standard measurement

The temperatures reported in the paper were measured by a team of outside collaborators from LLNL and UCSD who are skilled in a plasma measurement technique called Thomson scattering. To perform Thomson scattering, scientists use a very bright, very fast laser to fire pulses of green light into a plasma, which scatters off the electrons and provides information about their temperature and density.

“We are particularly grateful for the work of the collaborative team in helping us collect this data and refine key measurement techniques,” Levitt noted. Through measurements of hundreds of plasmas carried out through this collaboration, Zap now regularly collects Thomson scattering data on its latest generation equipment, FuZE-Q.

No external magnets, compression or heating required

Unlike the two mainstream fusion methods that have been the focus of most fusion research in recent decades, Zap’s technology does not require expensive and complex superconducting magnets or powerful lasers.

“Zap technology is orders of magnitude cheaper and faster to build than other devices, allowing us to quickly iterate and produce the cheapest thermal fusion neutrons. Compelling innovation economics are critical to launching commercial fusion products on time, ” said Benj Conway, CEO and co-founder of Zap.

In 2022, while collecting these results from FuZE, Zap commissioned its next generation device, FuZE-Q. While early results from FuZE-Q are not yet available, the device’s power bank can store ten times more energy than FuZE and is capable of scaling to higher temperatures and densities. At the same time, parallel development of power plant systems is also underway.

“We knew when we started Zap that we had a technology that was unique and beyond the status quo, so clearly crossing this high electron temperature mark and seeing these results in a top physics journal was significant validation,” Conway said. “We do face huge challenges, but we have all the ingredients to address them.”