In the quest to harness fusion energy, understanding the behavior of fast ions is crucial. These charged particles, born from processes like neutral beam injection (NBI), play a pivotal role in sustaining the fusion reaction. However, measuring their distribution in 3D or 4D phase-space is a complex endeavor, often likened to solving an ill-conditioned inverse problem. Enter O. Hyvärinen from the Department of Mathematics and Statistics at the University of Helsinki, who has developed a novel method to tackle this challenge.
Hyvärinen’s approach, detailed in a recent study published in the journal *Nuclear Fusion* (formerly known as *Fusion Energy*), leverages the ASCOT orbit-following code to encode the correlations between phase-space elements caused by neoclassical transport due to Coulomb collisions. This physics-informed prior information is then used to reconstruct the fast-ion distribution function.
“By using ASCOT, we can compute neoclassical anisotropic slowing-down distributions for a JET equilibrium as basis functions,” Hyvärinen explains. “This allows us to reconstruct the fast-ion distribution in a 4D phase-space with a high degree of accuracy.”
The method involves dividing the fast-ion distribution at each injection energy into separate basis functions based on flux surfaces of the ionized neutrals. Detailed data from the NBI geometry was used to compute basis functions at full, half, and one-third injection energies. Reconstructions based on synthetic data were then computed by solving for basis function coefficients with Tikhonov regularization.
While the reconstructions from one NBI matched well with the true solution, the addition of another NBI reduced the quality of the reconstructions significantly. This finding underscores the complexity of the problem and the need for further refinement of the method.
The implications of this research are profound for the energy sector. Accurate reconstruction of fast-ion distribution functions is essential for optimizing fusion reactions and improving the efficiency of fusion devices. By providing a more precise understanding of fast-ion behavior, Hyvärinen’s method could pave the way for advancements in fusion energy technology.
“Our method offers a promising approach to encoding neoclassical collisional physics as prior information in fast-ion distribution reconstructions,” Hyvärinen notes. “This could significantly enhance our ability to model and control fusion reactions, bringing us one step closer to realizing the full potential of fusion energy.”
As the world continues to seek sustainable and clean energy sources, research like Hyvärinen’s plays a vital role in shaping the future of the energy sector. By pushing the boundaries of what is possible, scientists and engineers are inching closer to making fusion energy a practical reality.