A newly published Zap Energy paper in Nuclear Fusion describes the most thorough neutron energy isotropy measurements yet from the FuZE device. This breakthrough strengthens evidence that the sheared-flow-stabilized Z pinch method used by Zap Energy produces a stable, thermal fusion environment and shows potential for expanding to higher energy outputs on the FuZE-Q platform.
"Essentially, this measurement indicates that the plasma is in a thermodynamic equilibrium," says Zap's Chief Scientist and Co-Founder, Uri Shumlak. "That means we can double the size of the plasma and expect the same sort of equilibrium to exist."
In the FuZE core, hydrogen nuclei fuse into helium, sending out high-energy neutrons that contain most of the reaction's power. More neutrons typically mean more fusion energy. Thermal fusion - created by intense heat and pressure - is Zap's target because its neutron output rises exponentially with increasing plasma current. On the other hand, beam-target fusion occurs when a fast-moving hydrogen nucleus hits a stationary target, indicating an out-of-equilibrium plasma that does not scale as effectively toward net power production.
"If we saw neutrons primarily from a beam-target source, it would mean that our machine wouldn't be scalable. We couldn't get to net energy production," explains Rachel Ryan, a senior scientist at Zap Energy and lead author of the paper. To test for neutron isotropy, the team used multiple detectors around FuZE and analyzed 433 identical shots. Almost all the measurements showed highly uniform neutron energies.
Historically, Z pinch devices date back to the 1950s. Early experiments on the Zero Energy Thermonuclear Assembly (ZETA) appeared successful, but the resulting fusion came mostly from beam-target interactions caused by plasma instabilities. That meant the system could not generate net energy. Since then, skepticism has followed pinch approaches. Other devices like the dense plasma focus also face challenges because their primary neutrons often emerge from beam-target collisions.
Zap Energy remains vigilant about ensuring its fusion stems from thermal processes. The company first detected thermal fusion in 2018. These new isotropy tests, performed at higher precision and energy, further confirm that sheared flows help postpone the instabilities that foiled earlier Z pinch methods. "This is why we put so much effort into making these precise measurements," Shumlak notes.
Ryan, who joined Zap in 2023, oversees neutron instrumentation and testing, building on foundational work by collaborators at Lawrence Livermore National Lab. The next step is to conduct similar isotropy tests under higher-energy conditions on FuZE-Q, where initial observations are encouraging. The paper also notes that near the end of each shot, the neutrons showed reduced isotropy, likely reflecting a breakdown phase where the pinch becomes unstable. Understanding this terminal phase could point the way toward preventing premature plasma disruption and boosting both the duration and performance of fusion operations.
Research Report:Time-resolved measurement of neutron energy isotropy in a sheared-flow-stabilized Z pinch
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