Lightning strikes 12 times per minute on fusion engineering test platform

Zap Energy has advanced its Century fusion engineering test platform to operate for more than one hundred plasma shots at 0.2 Hz, or one shot every five seconds, with the resulting heat captured by surfaces coated with circulating liquid metal.

Concentrated inside a vacuum chamber about the size of a hot water heater, each plasma carried up to 500 kA of current—about 20 times stronger than a bolt of lightning—discharged into a vessel lined with flowing liquid bismuth. During the record run, Century's total input power was 57 kilowatts, with 39 kilowatts delivered directly to the cables leading to the plasma chamber.

Compared with Century's commissioning milestone in 2024, this achievement represents an increase of 20 times in sustained average power and is a major step toward developing commercial fusion power plants using repetitive pulsed power and liquid metal energy transfer.

Now Fusion Science and Technology has published a paper on Century's design and its commissioning runs between June and October 2024.

Integrating fusion plant technologies

Century replicates the commercial engineering conditions of Zap's unique approach to fusion, which doesn't rely on superconducting magnets or high-intensity lasers. Instead, Zap's sheared-flow-stabilized (SFS) Z-pinch fusion modules drive a pulse of electricity through a flowing plasma stream, generating a magnetic field that compresses the plasma, as well as stabilizing forces that sustain it.

"Prolonged operations of a fully integrated, repetitively pulsed system at 30 kilowatts gives us a much clearer picture of what a sheared-flow Z-pinch fusion power plant will actually look like," said Matthew Thompson, VP of Systems Engineering at Zap Energy. "Century's real-world tests of our engineering subsystems mean we've already begun to identify and solve many of the most difficult commercial technology challenges."

One of Century's goals is to characterize energy transfer among three key power plant subsystems: repetitive pulsed power (frequent bursts of energy); liquid metal walls (for absorbing and transferring fusion energy out of the plasma chamber); and durable electrodes (components capable of surviving extreme conditions). These technologies are essential to building a commercial fusion system that will steadily generate energy over a sustained period.

Since first operations last year, each of Century's subsystems has been upgraded with the goal of reaching the 30 kW milestone. Upgrades include:

• A liquid metal loop circulating 2,500 pounds (1,100 kilograms) of flowing bismuth. The liquid bismuth acts as an electrical conduction path, a plasma-facing protective barrier, and a heat transfer fluid.
• A liquid metal first wall using centrifugal forces to cover more exposed solid metal surfaces, improving its ability to absorb plasma heat.
• A custom-built 200-kilowatt air-cooled heat exchanger that helps maintain thermal equilibrium.
• A redesigned nose cone, tipped with liquid metal to prevent cathode erosion.
• A high-flow cathode surge cooling system that helps quickly reduce system temperature between shots.

"Century is maturing technologies that will ultimately convert energy from our fusion reactions into electricity or industrial heat—systems engineering has historically been overlooked in fusion development," said Benj Conway, CEO and co-founder of Zap Energy. "Fusion is not just a plasma problem. It's a systems integration problem."

How Century works

Each Century shot begins in its power banks: a set of large-scale capacitors pulls energy from the grid, stores it briefly, and then releases a short burst of current into the top of Century's vacuum chamber via heavy-gauge cabling. Inside the vertically-oriented plasma chamber, modeled after a Zap FuZE device, the pulse ionizes a puff of hydrogen gas into an extremely hot, dense filament of plasma.

Because its design objective is engineering validation, Century operates with plain hydrogen or helium gas, rather than fusion-grade deuterium-tritium fuel. As a result, its plasmas do not undergo fusion reactions or emit neutrons.

Finally, thermal energy from the plasma reaches the flowing liquid metal wall that coats the plasma chamber inner surface. The circulating metal absorbs the plasma's thermal energy, transfers it to an air-cooled heat exchanger, and then returns to the vacuum chamber.

Scaling up

Since its commissioning in June 2024, Century has increased its capacity from single plasma shots every 10 seconds at ~1.4 kilowatt of average power, to one shot every five seconds, at ~30 kilowatts of average power. In February 2025, the DOE certified the completion of a three-hour Century campaign producing more than one thousand consecutive plasma shots, each with at least 100 kiloamps of current. In the past year, the platform has fired more than ten thousand shots across a wide range of configurations, providing valuable lessons about how to operate high-repetition-rate Z-pinch plasmas.

Over the coming months, Zap will continue to investigate critical technical questions while gradually ramping up Century's repetition rate and power levels.