SPARC positioned to demonstrate fusion power breakeven

SPARC — a compact, superconducting tokamak — uses magnetic confinement to achieve the burning plasma conditions necessary for fusion power plants.

SPARC may become the first commercial project to achieve net fusion gain — the ratio of power output to auxiliary power supplied — greater than unity (Q>1). But to ensure all the resources put into SPARC lead to a positive result, researchers using SPARC need to be confident of their measurement techniques. Raj et al. have planned three independent methods to measure SPARC’s output power.

“SPARC will make more fusion power than heating power it puts into the plasma, which has not been done so far in the magnetic confinement fusion sector,” said author Prasoon Raj.

The three techniques for measuring SPARC’s fusion power all complement one another. The first measures the global flux of neutrons from plasma, which requires careful in-vessel calibration and modeling of the neutron counters. The second looks at neutrons’ spectrum and spatial map to measure the device’s fusion rate, and the third calculates the fusion rate from the profiles of plasma temperature, density, and fuel. By relying on different physics, the combination of measurements avoids systematic errors that can arise from single instruments.

“That rigor matters for SPARC. Its Q>1 result will set a major scientific milestone and guide decisions across a multi-billion-dollar industry worldwide, so the number must hold up to scrutiny from physicists, investors, and the public alike,” Raj said. “When all three agree, no single hidden error can explain the result.”

SPARC is being constructed by commercial fusion energy company Commonwealth Fusion Systems in Massachusetts. The company has begun SPARC commissioning work and plans to turn the machine on in 2027 to begin the campaign for the Q>1 mission.

“SPARC carries the hopes of many fusion scientists around the world, and the speed and grit with which the team and wider community are pursuing it are already inspiring,” Raj said.

Source: “Measurements for fusion power to demonstrate Q_fus>1 on SPARC,” by P. Raj, I. Abramovic, J. L. Ball, D. J. Battaglia, J. Carmichael, A. Celora, M. Dalla Rosa, N. G. Duarte, E. Fox-Widdows, B. Frandeen, J. Frenje, Z. Ghani, R. Gocht, G. Gorini, M. Haken, J. N. Hawke, A. Hoffmann, I. Holmes, D. Kelley, R. Kennedy, M. LaCapra, R. Z. Lupo, B. C. Lyons, S. Mackie, S. McKanas, C. E. Myers, V. Nikolaeva, M. Nocente, E. Panontin, J. Pentecost, M. Quinn, M. Rebai, J. Rice, D. Rigamonti, K. Rohan, A. Rosenthal, A. A. Saltos, S. Scully, M. Silva Sa, P. B. Snyder, I. Song, A. A. Teplukhina, R. A. Tinguely, M. Tardocchi, D. Vezinet, X. Wang, C. Woodall, and M. L. Reinke, Review of Scientific Instruments (2026). The article can be accessed at https://doi.org/10.1063/5.0349670 .

This paper is part of the Proceedings of the 26th Topical Conference on High-Temperature Plasma Diagnostics Collection, learn more here .