Zap Energy Hits First DoE Milestone

In May of 2023, Zap Energy was announced as a participant in the U.S. Department of Energy’s Milestone-Based Fusion Development Program. Last week, Zap Energy officially met its first major technology milestone under the program, with results validated by a panel of independent experts. 

While many of the startups participating in the DoE program are exploring designs that require high-powered magnets or lasers, Zap Energy is taking a different approach. They’re advancing the Z-pinch concept, using pulsed electric currents to generate a magnetic field that compresses plasma to fusion conditions. Z-pinches are inherently unstable, but Zap solves for this by introducing velocity shear (moving plasma layers at different speeds), which suppresses plasma instabilities and allows for more stable confinement.

To meet the first milestone outlined in the program, Zap Energy’s test system, named Century, operated continuously for three hours and produced a series of 1,080 plasma shots, with each shot powered by at least 100 kA of input current. The reactions occurred inside a chamber with flowing liquid bismuth walls, using a cathode with a liquid metal tip designed to withstand the repeated high-energy discharges.

This achievement comes on the heels of Zap Energy’s prototype Z-pinch fusion core demonstrating nearly perfect neutron isotropy (a measure of how uniformly neutrons are emitted from the device). This development, published in the journal Nuclear Fusion, offers strong evidence that the sheared-flow-stabilized Z-pinch approach produces stable conditions for fusion, and implies that the system could potentially maintain stability as it's scaled up.

Where do they go from here?

Despite the recent wins, Zap Energy has yet to achieve scientific breakeven, and commercial viability is a long way off. During last month’s milestone demonstration, Century operated at a rate of one shot every 10 seconds. At power plant scale, the team plans to increase the firing frequency to approximately 10 times per second. Another challenge is adding more electric current into the pinch itself: the more current, the more heat and density produced, and the better conditions for fusion. These conditions also impose stricter requirements on cathode design, since the plasma interacts directly with a solid surface. In parallel with these core materials engineering challenges, Zap Energy is also working on the operational challenges associated with power plant engineering.

If Zap Energy’s approach continues to scale, they could find themselves well positioned in the fusion race. Their reactor design offers a much smaller form factor compared to other approaches, effectively a 3-meter by 3-meter cylinder consisting of a metal tube surrounded by a wall of molten metal. Their design also doesn’t require the same high-temperature superconducting magnets needed for stellarator and tokamak-based approaches (nor the requirement to protect those expensive magnets from heat load and neutron flux). It’s a promising approach, and one that we’ll continue to follow closely.