Fusion Energy Cannot Scale Without Better Sensors - A Federal Report Makes the Case

Before a fusion power plant can generate electricity for the grid, it needs to do something that sounds deceptively simple: measure what is happening inside it. Plasma temperatures in a fusion reactor can reach 100 million degrees Celsius. Pressures fluctuate in microseconds. Fuel density shifts constantly. Any commercial fusion system will need sensors capable of monitoring all of this accurately, continuously, and without being destroyed by the radiation environment they operate in.

Those sensors do not yet fully exist. A report released by the U.S. Department of Energy makes the case that closing that gap is one of the most critical steps on the path to commercial fusion power - and that the federal investment required has not yet materialized at the necessary scale.

The report was produced through the DOE's 2024 Basic Research Needs Workshop on Measurement Innovation, organized under the Office of Science's Fusion Energy Sciences program. It was chaired by Luis Delgado-Aparicio, head of advanced projects at the Princeton Plasma Physics Laboratory, and co-chaired by Sean Regan, a distinguished scientist and director of the Experimental Division at the University of Rochester's Laboratory for Laser Energetics. Seventy researchers from academia, private industry, and national laboratories contributed.

Seven Physics Domains, Seven Sets of Measurement Gaps

The report covers seven areas of plasma physics funded by the DOE's Fusion Energy Sciences program: low-temperature plasma, high-energy-density plasma, plasma-material interaction, burning plasma from magnetic-confinement fusion (MCF), burning plasma from inertial-confinement fusion (ICF), MCF-based fusion pilot power plants, and ICF-based fusion power plants.

Each domain has distinct measurement challenges. Low-temperature plasma, used in semiconductor fabrication and materials processing, requires sensors that can operate in chemically reactive environments. High-energy-density plasma - the kind created by powerful lasers - produces conditions that last for billionths of a second, far faster than conventional diagnostics can resolve. Burning plasma in a magnetic confinement device such as a tokamak must be monitored without disturbing the delicate magnetic equilibrium that contains it.

Perhaps the most pressing challenge is for fusion pilot plants. Future reactors will produce intense neutron radiation that can damage or destroy the sensors embedded within them. No commercially viable radiation-hardened diagnostic system currently exists at the scale a power plant would require.

Seven Recommendations

The report's working groups identified seven priority research opportunities. First: validate and verify design modeling codes using artificial intelligence, machine learning, and digital twins to accelerate the development of new sensors. Second: establish a national network for measurement innovation - modeled after the successful LaserNetUS facility-sharing program - that the report suggests could be called CalibrationNetUS. Third: form national teams to efficiently convert new diagnostic concepts into working instruments. Fourth: standardize calibration protocols across the field, which currently lacks consistent practices. Fifth: transfer diagnostics expertise and hardware from DOE national laboratories to the growing private fusion sector. Sixth: invest heavily in workforce development, which the report describes as requiring a "momentous" effort given the complexity of the skills needed. Seventh: begin planning now for the remote operation and maintenance of future fusion plants, an area the report flags for dedicated follow-up workshops.

"Measurement innovations have led and will continue to lead to scientific and engineering breakthroughs in plasma science and technology," Delgado-Aparicio said. "This new report provides substantive findings across seven key areas. We believe it will impact both the public and private fusion communities in a meaningful way."

Private Fusion's Growing Stake

The timing of the report reflects a significant shift in the fusion landscape. Private investment in fusion companies has accelerated rapidly, with dozens of startups now pursuing commercial reactor designs on compressed timelines. Many of these companies depend on the same diagnostic technologies developed at public research facilities - and some are building fusion concepts that will require measurement capabilities beyond anything currently tested.

The report explicitly addresses the need to transfer public-sector diagnostic expertise to private facilities. Without that transfer, private fusion developers will face a bottleneck: they can build plasma devices, but they cannot fully characterize what is happening inside them.

The DOE's Fusion Science and Technology Roadmap targets actions and milestones through the mid-2030s. The measurement innovation report is designed to feed directly into that timeline, identifying the specific technical gaps that must be closed before the roadmap's goals are achievable.