Zap Energy Achieves DOE Milestones for Fusion Capacitor Development
The U.S. Department of Energy (DOE) has approved two capacitor development milestones for Zap Energy under the Milestone-Based Fusion Development Program. These approvals cover a detailed design for a pulsed power capacitor engineered for the repetition rate and operating lifetime required in a fusion power plant, and a prototype capacitor designed, manufactured, and tested by Zap Energy.
These milestones indicate advancements in long-life capacitor design and the U.S.-based manufacturing capabilities necessary for large-scale production of these components. Pulsed power, delivered by high-voltage capacitor banks, is a critical technology for various fusion energy approaches, including Zap Energy’s sheared-flow-stabilized Z pinch. Developing capacitors that can operate at high repetition rates over billions of pulses is a step toward commercial fusion power plants.
Commercial Fusion Requirements
Zabrina Johal, CEO of Zap Energy, stated that commercial fusion requires reliable, repeatable, and power-plant-scale operation of technologies surrounding the fusion core. She noted that pulsed power is a critical enabling technology, and these milestones demonstrate progress toward the long-life, high-repetition-rate systems needed for commercial fusion plants, while also building manufacturing capability within the United States.
Pulsed power capacitors store electrical energy and release it in rapid bursts. In pulsed fusion, these bursts help drive fuel into extreme conditions for fusion reactions. While commercial units are typically rated for about 100,000 pulses, a commercial power plant operating for 20 years at 10 pulses per second would require individual capacitors to withstand approximately 6 billion pulses.
Capacitor Specifications and Testing
Zap Energy's detailed design is for a 35-kilovolt, actively-cooled capacitor rated for 50,000 amps of peak current, projected to last 6 billion pulses. It incorporates self-healing metallized polypropylene film, which degrades gradually, and uses multiple capacitor sections in series to reduce the voltage seen by the film. Integrated active cooling enables continuous operation at 10 pulses per second.
The prototype is a compact, 2.8-pound epoxy-potted capacitor using the same multi-section winding approach. Zap Energy performed the winding, arc spraying, assembly, potting, and testing in-house, cycling the unit hundreds of times at 8 kilovolts and over 7,000 amps. Its capacitance remained stable within 0.25% throughout the test campaign, exceeding all prototype milestone criteria.
Supply Chain and Future Development
Ryan Umstattd, Zap’s VP of Federal Programs, explained that a goal of the DOE Milestone Program is to support the fusion supply chain across various fusion approaches and establish new U.S.-based manufacturing. He added that while long-lifetime, high-repetition-rate capacitors will eventually be needed by the thousands in fusion power plants, the initial step involves developing designs, manufacturing techniques, and qualification standards.
These approvals followed a review by an independent panel of experts convened by the DOE. Zap Energy's next steps include testing the designs to higher voltages, longer lifetimes, and with voltage reversals for implementation in future Zap fusion power banks.