Spin-Polarized Fuels for Enhanced Tritium Burn Efficiency in Fusion Energy Systems

Magnetic confinement fusion power plants face a fundamental challenge in efficiently utilizing tritium fuel, a critical and limited resource. While increasing tritium burn efficiency (TBE)—the fraction of injected tritium that fuses—is desirable for fuel self-sufficiency and reducing inventory, existing approaches encounter an inherent trade-off: higher TBE leads to increased helium ash concentration in the core plasma. This ash dilutes the fuel, significantly reducing fusion power density and demanding higher energy confinement, thereby limiting overall plant performance. Consequently, achieving high TBE without compromising fusion output remains a major hurdle, requiring advanced divertor designs and selective helium pumping technologies that are still under development. Furthermore, low TBE necessitates impractical tritium breeding ratios and large, costly start-up inventories, complicating the design and operation of the complex tritium fuel cycle.

The invention utilizes spin-polarized deuterium-tritium (D-T) fusion fuel, where the nuclei are spin-aligned before injection into a fusion plasma. This process, which requires a dedicated fuel polarization device, aims to increase the D-T fusion cross-section by approximately 50%. The core technical feature is enabling an order-of-magnitude improvement in tritium burn efficiency (TBE) without reducing fusion power density, a limitation of previous methods. By enhancing the burn fraction, the invention allows for a higher deuterium-to-tritium ratio in the fuel mix, which in turn significantly reduces the required tritium inventory for fusion power plants, both for initial startup and ongoing operation. While the concept is theoretically sound, the survivability of nuclear spin polarization within a hot, fusion-relevant plasma environment remains to be experimentally demonstrated.        

Applications

1. Fusion Energy Production: The invention directly enhances the economics, safety, and performance of D-T magnetic fusion power plants by significantly increasing tritium burn efficiency and reducing tritium inventory. 
2. Specialized Fusion Fuel Technology and Equipment: The invention necessitates the development, manufacturing, and supply of specialized equipment for spin-polarized fuel production, injection, and in-plasma diagnostics. 
3. Fusion Reactor Design and Engineering: The invention enables the design of more compact, cost-effective, and higher-performing fusion reactors due to increased power density and reduced tritium requirements.

Advantages

1. Overcoming the TBE-Power Density Trade-off: Unlike existing approaches where increasing tritium burn efficiency (TBE) leads to increased helium ash and fuel dilution, thereby reducing fusion power density in tokamaks (e.g., DIII-D, JT-60U, JET), this invention uniquely increases TBE by an order of magnitude *without* sacrificing fusion power output, and can even enhance it.
2. Reduced Tritium Inventory Requirements: Compared to current fusion fuel cycle models for ARC- and STEP-class tokamaks that require large tritium startup and operational inventories (e.g., 2-8 kg for STEP), this invention can reduce these amounts by an order of magnitude, addressing critical supply, safety, and cost challenges associated with tritium.
3. Improved Fusion Plant Economics: By significantly reducing the required tritium inventory and potentially enabling more compact reactor designs due to enhanced power density and burn efficiency, the invention lowers capital and operational costs compared to conventional D-T fusion approaches.
4. Enhanced Fusion Power Output: Spin polarization of D-T fuel can increase the fusion cross-section by ~50%, leading to a potential ~90% increase in net electric power output for a given reactor design, allowing for more power from the same size plant or a smaller plant for the same power, unlike unpolarized fuel.
5. Enhanced Safety: A direct consequence of the order-of-magnitude reduction in on-site tritium inventory is a significant improvement in the safety profile of fusion power plants, mitigating risks associated with handling and storing large quantities of radioactive tritium compared to current plant designs.