Spin Polarized Fuel Evaluation Project 

The Stellar Energy Foundation announced in January 2025 its funding of a groundbreaking research project to evaluate the use of spin-polarized fuel in magnetic confinement fusion devices.

Spin-polarized fuel could transform fusion reactor development by enabling more compact plant designs, easing the requirements to reach high plasma gain, and optimizing the distribution of emitted fusion neutrons. These advantages could significantly reduce capital costs and technical risks while improving tritium breeding efficiency in commercial fusion power plants.

Using modern computational tools, the research will analyze depolarization rates of spin-polarized fusion fuel in fusion power plants—a crucial step in determining whether spin-polarized fuel can be practically implemented at scale.

This initiative comes amid renewed interest in spin-polarized fusion fuel across the fusion energy sector. The Department of Energy’s ARPA-E recently convened a workshop on the topic, while the Office of Fusion Energy Sciences has launched an experimental program at DIII-D to measure spin-polarized fuel effects in magnetic fusion devices.

The project is advised by leading plasma physics experts from the Princeton Plasma Physics Laboratory: Principal Research Physicist Dr. Ahmed Diallo and Staff Research Physicists Dr. Jason Parisi and Dr. Jacob Schwartz. The project also includes Marathon Fusion researcher Hina Ali and Chief Technology Officer Adam Rutkowski, along with plasma physics expert Dr. James Cook.

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Background Information: Spin Polarized Fuel for fusion reactions

The idea of polarizing the nuclear spins in a deuterium-tritium (D-T) fusion reaction is based on the quantum mechanical properties of nuclear interactions.  Polarization of the “fuel” in a fusion energy system enhances the efficiency of the fusion reaction:

Spin Alignment and Cross-Section Enhancement

  • In nuclear fusion, the reaction cross-section (which determines the probability of fusion occurring) depends on the relative spin states of the reacting nuclei.
  • Deuterium (D) and tritium (T) each have a nuclear spin of 1 and ½, respectively, and they can be either aligned (parallel) or anti-aligned (antiparallel).
  • It’s well known that the probability of deuterium-tritium fusion can be increased by preparing the fuel with certain spin alignments, because a specific reaction can occur for only some combinations of reactant spin.
  • Theoretical studies have indicated that spin-polarized fusion can increase the reaction rate by 1.5x under certain conditions.
  • Experimental efforts (e.g., spin-polarized targets in nuclear physics) support the feasibility of achieving polarized fusion plasmas, provided technical challenges can be overcome.

Directional Emission of Fusion Products

  • In a conventional D-T reaction, the fusion products (a 14.1 MeV neutron and a 3.5 MeV alpha particle) are emitted isotropically (in random directions).
  • If the nuclear spins are aligned, the reaction products may become anisotropically distributed (favoring certain directions), which could be useful for controlling energy deposition in a fusion system.

For example, if the fast neutrons are preferentially emitted in a particular direction, the fusion system‘s blanket design could be optimized to capture their energy more efficiently and potentially reduce the system’s capital cost.