Advancing nuclear fusion: Understanding vortex rings to improve fuel compression and energy efficiency

A recent study conducted by researchers at the University of Michigan has shed light on the formation of vortex rings, which are swirling, ring-shaped disturbances. Understanding the formation of these vortex rings could greatly benefit nuclear fusion researchers in their quest to achieve more efficient fuel compression, bringing us closer to harnessing fusion as a viable energy source.

The model developed by the researchers has implications beyond nuclear fusion. It could aid engineers in designing fuel capsules that minimize energy loss during the ignition of the fusion reaction, an essential process in creating the conditions found in stars. Additionally, the model could assist engineers working on supersonic jet engines, as well as physicists seeking to comprehend phenomena like supernovae and the mixing of fluids after shock waves pass through.

Vortex rings play a crucial role in both the formation of celestial bodies and fusion implosions. As collapsing stars emit vortex rings, they disperse materials that eventually give rise to nebulae, planets, and even new stars. Conversely, during fusion implosions, inward-moving vortex rings disrupt the stability of the burning fusion fuel, reducing the efficiency of the reaction.

By elucidating the formation process of vortex rings, this research offers valuable insights into extreme events occurring in the universe. Moreover, it brings us closer to harnessing the power of nuclear fusion as a sustainable energy source.

Nuclear fusion involves the merging of atoms, resulting in the release of significantly more energy than atomic fission, which powers current nuclear plants. While scientists have been able to create fusion reactions, a significant amount of energy is wasted in the process.

One of the challenges lies in effectively compressing the fuel. Instabilities cause the formation of jets that penetrate the fusion hotspot, leading to fuel leakage between them. To illustrate this, imagine trying to squeeze an orange with your hands, and how the juice would escape between your fingers.

The researchers have demonstrated that vortex rings forming at the forefront of these jets share mathematical similarities with smoke rings, eddies trailing behind jellyfish, and plasma rings emanating from the surface of supernovae.

In conclusion, this research on vortex ring formation not only has implications for nuclear fusion but also provides insights into various natural and engineered processes. By better understanding vortex rings, we can enhance fuel compression and improve the efficiency of fusion reactions, potentially unlocking the vast energy potential of nuclear fusion.

One of the most well-known approaches to nuclear fusion involves a setup using a spherical array of lasers aimed at a spherical fuel capsule. This configuration is utilized in experiments conducted at the National Ignition Facility, where they have achieved record-breaking energy outputs in recent years.

In this setup, the lasers vaporize the material surrounding the fuel, which is typically a precisely manufactured diamond shell in the most recent breakthrough in December 2022. As the shell vaporizes, it drives the fuel inwards while the carbon atoms are propelled outward, generating a shockwave. This intense compression results in the fusion of hydrogen atoms.

Although the fuel pellets used in these experiments are exceptionally round, they deliberately include a fill tube through which the fuel is injected. Similar to a straw inserted into a crushed orange, this fill tube is the most likely location for a jet formed by vortex rings during the compression phase.

Eric Johnsen, an associate professor of mechanical engineering at U-M who supervised the study, explained that in fusion experiments, the formation of the jet only needs to be delayed by a few nanoseconds, as the process unfolds rapidly.

The research project involved a collaboration between experts in fluid mechanics, such as Michael Wadas and Eric Johnsen, and specialists in nuclear and plasma physics, including Carolyn Kuranz, an associate professor of nuclear engineering and radiological sciences.

While the existence of these structures in fusion experiments and astrophysical observations has been noted in previous high-energy-density physics studies, they have not been explicitly identified as vortex rings until now, according to Wadas.

Drawing on the extensive body of research on these structures in fusion experiments and astrophysics, Wadas and Johnsen were able to build upon and expand existing knowledge, rather than treating them as entirely novel features.

Johnsen’s interest extends to the possibility that vortex rings play a role in driving the mixing of heavier and lighter elements during stellar explosions, which is necessary to account for the composition of planets like Earth.

The model developed in this study can also assist researchers in understanding the energy limits of vortex rings and how much fluid can be displaced before the flow becomes turbulent, making it more challenging to model accurately. Ongoing work by the team involves validating the vortex ring model through experimental verification.

The findings of this research have been published in the journal Physical Review Letters.

Source: University of Michigan

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