A new study published this month in Physical Review Letters reports on measurements taken from Zap Energy's Fusion Z-pinch Experiment (FuZE), indicating plasma electron temperatures between 1-3 keV - equivalent to about 11 to 37 million degrees Celsius (20 to 66 million degrees Fahrenheit). Achieving these temperatures is crucial for fusion systems, and FuZE represents the simplest, smallest, and least expensive device to accomplish this feat. Zap's technology may lead to a significantly shorter and more feasible route to a commercial product that can provide plentiful, on-demand, carbon-free energy worldwide.
"These are meticulous, unequivocal measurements, yet made on a device of incredibly modest scale by traditional fusion standards," said Ben Levitt, VP of R and D at Zap. "We've still got a lot of work ahead of us, but our performance to date has advanced to a point that we can now stand shoulder to shoulder with some of the world's pre-eminent fusion devices, but with great efficiency, and at a fraction of the complexity and cost."
The FuZE project initially received funding for research at the University of Washington from the U.S. Department of Energy's Advanced Research Projects Agency - Energy (ARPA-E). The device was later moved to Zap Energy's dedicated R and D facilities in 2020, shortly after the company's inception. The data presented in the study were collected in 2022 during an ARPA-E supported collaboration with researchers from Lawrence Livermore National Laboratory (LLNL) and the University of California, San Diego, who played a key role in developing the measurement system.
"Over many decades of controlled-fusion research, only a handful of fusion concepts have reached 1-keV electron temperature," noted Scott Hsu, Lead Fusion Coordinator at the DOE and former ARPA-E Program Director. "What this team has achieved here is remarkable and reinforces ARPA-E's efforts to accelerate the development of commercial fusion energy."
The first step to initiating fusion involves generating a plasma - an energetic "fourth state of matter" where nuclei and electrons are unbound and flow freely. By compressing and heating a plasma comprised of hydrogen isotopes deuterium and tritium, their nuclei collide and fuse, releasing approximately 10 million times more energy per ounce than burning an equivalent amount of coal.
Although fusion reactions have been demonstrated in the laboratory for decades, the challenge remains to produce more output energy from these reactions than the energy input required to initiate them.
Zap Energy's approach, utilizing a Z pinch where large electric currents are passed through a plasma, creates its own electromagnetic fields that heat and compress the plasma. While Z-pinch fusion has been experimented with since the 1950s, its potential has been limited by the brief lifespans of its plasmas. However, Zap has overcome this challenge by implementing a dynamic flow through the plasma, a technique called sheared-flow stabilization.
"The dynamics are a wonderful balancing act of plasma physics," Levitt explained. "As we climb to higher and higher plasma currents, we optimize the sweet spot where the temperature, density, and lifetime of the Z pinch align to form a stable, high-performance fusing plasma."
Zap's detailed measurements show that electron temperatures and fusion neutron production peak simultaneously, supporting the idea of a thermally balanced fusing plasma, according to the company.
"The results in this paper and further tests we've done since, all paint a good overall picture of a fusion plasma with room to scale toward energy gain," said Uri Shumlak, co-founder and Chief Scientist at Zap Energy. "Working at higher currents we're still seeing sheared flow extending the Z-pinch lifetimes long enough to produce very high temperatures and the associated neutron yields we'd predict from modeling."
The temperatures in the study were measured using a technique known as Thomson scattering, where a high-intensity, fast laser pulse of green light is fired into the plasma, scattering off the electrons and providing data about their temperature and density.
"We're especially grateful to the collaboration team for the work they did to help gather this data and refine a critical measurement technique for us," Levitt noted.
In contrast to other mainstream fusion approaches that rely on costly superconducting magnets or powerful lasers, Zap's technology requires neither, making it significantly less expensive and faster to build. "Zap tech is orders of magnitude less expensive and quicker to build than other
devices, allowing us to iterate rapidly and produce the cheapest thermal fusion neutrons out there. Compelling innovation economics are vital to launching a commercial fusion product on a timescale that matters," commented Benj Conway, CEO and co-founder of Zap.
In 2022, the same year these results were collected, Zap commissioned its next-generation device, FuZE-Q. While preliminary results from FuZE-Q are still forthcoming, the device features a power bank with ten times the stored energy of FuZE and the capacity to achieve much higher temperatures and densities. Parallel development of power plant systems is also in progress.
"We started Zap knowing we had a technology that was unique and outside the status quo, so definitively crossing this high electron temperature mark and seeing these results in a premier physics journal is major validation," Conway stated. "We've certainly got big challenges ahead, but we have all the ingredients to solve them."
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