Lifeboat Foundation

Physicists have been trying to design fusion reactors, technologies that can generate energy via nuclear fusion processes, for decades. The successful realization of fusion reactors relies on the ability to effectively confine charged particles with magnetic fields, as this in turn enables the control of high-energy plasma.

It turns out that the evolution of the most violent collisions between nuclei, as they are studied at the Large Hadron Collider at CERN, depends on the initial conditions, namely the geometry and shape of the colliding nuclei, which are in their ground state. More surprisingly, this insight also allows us to determine properties of the colliding nuclei that cannot easily be studied by other methods.

The researchers have predicted how the shape changes and fluctuations of the colliding nuclei will influence the outcome of extreme high-energy conditions. This paves the way for further studies which will yield a better understanding of the dynamic behavior of nuclei. An article on the results has been published in Physical Review Letters.

The predictions are theoretical but based on an experiment at the world’s leading physics research center, CERN, Switzerland.

Can theory and computation methods help the search for the best divertor material and thus contribute to making fusion energy a reality?

Exploring nuclear fusion as a clean energy source reveals a critical need for advanced plasma-facing materials. MARVEL lab researchers identified materials that might withstand fusion’s extreme conditions and proposed alternatives to tungsten, the current choice.

Nuclear fusion and the material challenge.

Nuclear fission has powered our world and medical advancements for decades, yet some of its secrets have remained elusive.

One of the biggest puzzles? What exactly happens when an atom’s nucleus splits apart at its “neck rupture” point.

Aurel Bulgac, a physics professor at the University of Washington, has been delving into this very question. He and his team set out to simulate the intricate particle dance during this critical moment of fission.

Breaking the problem into pieces makes it easier to design a fusion reactor’s coils for optimum energy confinement.

In magnetic-confinement fusion, different reactor designs pose different trade-offs. Stellarators use external magnetic fields to confine plasma in the shape of a twisted donut. Such fields are relatively easy to maintain in a steady state, but optimizing their geometry to minimize energy loss is much more difficult. Tokamaks, in contrast, confine plasma in an axisymmetric geometry using magnetic fields partially generated via currents induced in the plasma. This geometry provides near-perfect confinement at the expense of stability and operational simplicity. José Luis Velasco of Spain’s Center for Energy, Environmental and Technological Research (CIEMAT) and his colleagues now present a new family of stellarator magnetic-field configurations that benefit from tokamak-like energy confinement [1].

Magnetic fusion designs achieve confinement using nested magnetic-flux surfaces. Ideally, each charged particle remains tied to a given surface contour and the plasma as a whole exhibits near-zero radial drift. Such a condition results in perfect confinement, aside from losses due to collisions among particles on the same contour. Tokamaks inherently avoid radial drift, but to achieve the same level of confinement in a stellarator means imposing constraints on each magnetic surface’s topology, sometimes requiring infeasible coil designs.

Nuclear fusion could be an ideal solution to mankind’s energy problem, guaranteeing a virtually limitless source of power without greenhouse gas emissions. But there are still huge technological challenges to overcome before getting there, and some of them have to do with materials.

“In low-energy experiments, it’s like taking a long-exposure picture,” said Chun Shen, a theorist at Wayne State University whose calculations were used in the new analysis.

Because the exposure time is long, the low-energy methods do not capture all the subtle variations in the arrangement of protons that can occur inside a nucleus at very fast timescales. And because most of these methods use electromagnetic interactions, they can’t directly “see” the uncharged neutrons in the nucleus.

“You only get an average of the whole system,” said Dean Lee, a low-energy theorist at the Facility for Rare Isotope Beams, a DOE Office of Science user facility at Michigan State University. Though Lee and Shen are not co-authors on the study, they and other theorists have contributed to developing this new nuclear imaging method.

By 2027, Germany will be drawing clean energy from a renewable source in Lingen that provides 300 MW electricity capacity generated from green hydrogen.

Researchers have been performing these experiments for nearly 30 years but they always encounter the same problem: the bottle technique yields an average neutron survival time of 880 s, while the beam method produces a lifetime of 888 s. Importantly, this eight-second difference is larger than the uncertainties of the measurements, meaning that known sources of error cannot explain it.

A mix of different neutron states?

A team led by Benjamin Koch and Felix Hummel of TU Wien’s Institute of Theoretical Physics is now suggesting that the discrepancy could be caused by nuclear decay producing free neutrons in a mix of different states. Some neutrons might be in the ground state, for example, while others could be in a higher-energy excited state. This would alter the neutrons’ lifetimes, they say, because elements in the so-called transition matrix that describes how neutrons decay into protons would be different for neutrons in excited states and neutrons in ground states.