U.S. Department of Energy Approves Zap Energy’s Fusion Capacitor Design and First Prototype
Zap designs a 35-kilovolt capacitor for six billion pulses and manufactures its first capacitor in house under the Milestone-Based Fusion Development Program
Pulsed power, delivered quickly and reliably by banks of high-voltage capacitors, is a key enabling technology for many approaches to fusion energy, including Zap Energy’s sheared-flow-stabilized Z pinch. Developing capacitors capable of operating at high repetition rates over billions of pulses is an important step toward commercial fusion power plants.
The U.S. Department of Energy (DOE) has approved two Zap Energy capacitor development milestones under the Milestone-Based Fusion Development Program: a detailed design for a pulsed power capacitor built for the repetition rate and operating lifetime needed in a fusion power plant, and a first prototype capacitor designed, manufactured and tested entirely at Zap. Together, the milestones demonstrate progress in both long-life capacitor design and the U.S.-based manufacturing capabilities needed to produce these components at scale.
“Commercial fusion requires more than achieving fusion conditions. It requires the technologies around the fusion core to operate reliably, repeatedly and at power-plant scale,” said Zabrina Johal, CEO of Zap Energy. “Pulsed power is one of those critical enabling technologies. These milestones demonstrate progress toward the long-life, high-repetition-rate systems a commercial fusion plant will need, while building the manufacturing capability to produce them here in the United States.”
Pulsed power capacitors store electrical energy and release it in fraction-of-a-second bursts. In pulsed fusion approaches, these bursts help drive the fuel into extreme conditions where fusion reactions can occur and release energy. Such capacitors are supplied by a small number of vendors worldwide, and commercial units are typically rated for around 100,000 pulses. At a repetition rate of 10 pulses per second, a commercial power plant operating over a 20-year life could require individual capacitors to withstand roughly 6 billion pulses.
Zap’s detailed design is a 35-kilovolt, actively-cooled capacitor rated for 50,000 amps of peak current and projected to last 6 billion pulses. It uses self-healing metallized polypropylene film, which degrades gradually rather than failing outright, and places several capacitor sections in series inside each winding so the film sees only a small fraction of the terminal voltage. Integrated active cooling allows continuous operation at 10 pulses per second (10 Hz).
The first prototype is a compact, 2.8-pound epoxy-potted capacitor built with the same multi-section winding approach. Zap wound, arc sprayed, assembled, potted and tested the unit in house, cycling it hundreds of times at 8 kilovolts and over 7,000 amps along the way. Its capacitance held steady to within 0.25% across the full test campaign, exceeding every prototype milestone criterion.
“One goal of the DOE Milestone Program is to support parts of the fusion supply chain that enable progress across multiple fusion approaches, as well as establish new U.S.-based manufacturing,” explains Zap’s VP of Federal Programs Ryan Umstattd. “Eventually we expect long lifetime, high repetition rate capacitors to be bought off the shelf and needed by the thousands in fusion power plants, but first we need to develop the designs, manufacturing techniques and qualification standards that meet the necessary specifications.”
The approvals follow review of both milestones by an independent panel of experts convened by DOE. Zap’s next step is to test the designs to higher voltages, longer lifetimes, and with voltage reversals so that they can be implemented in future Zap fusion power banks.
About Zap
Zap Energy is building an integrated nuclear energy platform across advanced fission, fission-fusion hybrid and fusion technologies. The strategy pairs a near-term path to deployment through modular fission with differentiated hybrid technology and the long-term potential of fusion power. Fission systems provide the first path to market while building the manufacturing, operational and regulatory capabilities that support the broader platform. Hybrid systems are designed to use fusion neutrons to amplify fission power and unlock additional energy from spent nuclear fuel. Zap’s compact, sheared-flow-stabilized Z-pinch approach advances fusion without the large magnets or lasers required by other approaches. Shared capabilities in nuclear engineering, advanced materials, liquid metals and power systems allow each stage to accelerate the next, creating a foundation for scalable, reliable, carbon-free power.