Nuclear fusion is a widely studied process by which atomic nuclei of low atomic number fuse to form a heavier nucleus, while releasing a large amount of energy. Nuclear fusion reactions can be produced using a method known as inertial confinement fusion, which involves the use of powerful lasers to implode a fuel capsule and produce plasma.
Researchers from Massachusetts Institute of Technology (MIT), University of Delaware, University of Rochester, Lawrence Livermore National Laboratory, Imperial College London and University of Rome La Sapienza recently showed what happens to this implosion when a strong magnetic field is applied to the fuel capsule used for inertial confinement fusion. Their article, published in Physical examination lettersdemonstrates that strong magnetic fields flatten the shape of inertial fusion implosions.
“In inertial confinement fusion, a millimeter-sized spherical capsule is imploded using high-power lasers for nuclear fusion,” Arijit Bose, one of the researchers who conducted the study, told Phys .org. “Applying a magnetic field to implosions can attach charged plasma particles to the B-field and improve their chances of fusion. However, since the magnetic field can restrict plasma particle motion only in the direction across the field lines and not in the direction along the applied field lines, this may introduce differences between the two directions which affect the shape of the implosion.”
Over the past decade, several physicists have studied the possible effects of magnetizing fusion implosions. Most of their studies, however, were numerical in nature and did not test hypotheses in an experimental setting.
Bose and his colleagues therefore decided to conduct a series of tests to empirically determine what happens to the shape of inertial fusion implosions under strong magnetization. Their experiments were specifically designed to explore the properties of highly magnetized plasmas, producing unique plasma conditions. Under these conditions, both ions and electrons in the plasma are magnetized.
“It should be noted that the magnetization of plasma ions is very difficult to achieve and has not been studied with high-powered lasers,” Bose explained. “To conduct our tests, we used an extremely high magnetic field of 50T, far superior to those used in previous experiments, and used shocks to conduct the implosion experiments at the OMEGA laser facility. We found, for the first time, that this field flattened the shape of the implosion, so that it became more oblate.”
The researchers performed their experiments at the OMEGA Laser Facility, located at the Laser Energy Laboratory in Rochester, New York. Specifically, they applied high B-fields (i.e. with forces 1000 times greater than typical bar magnets) to a millimeter-sized spherical capsule, which was heated to over 100 million K using a laser shock.
“The shock heating and applied B-field produced unique plasma conditions with strongly magnetized electrons and ions that were important for the experiments,” Bose said. “Through simulations, we then determined that this oblate shape is caused by the suppression of heat flux (perpendicular to the direction of the magnetic field) in the highly magnetized plasma.”
Recent work by this team of researchers provides valuable new insights into inertial meltdown implosions and the effects that magnetic fields can have on them. In the future, the method they described could be used by other teams to produce highly magnetized electrons and ions in experimental environments, using high-powered lasers.
“Specifically, we were the first to observe that the applied magnetic field flattened the shape of the implosion,” Bose added. “In our next studies, we plan to use the “recipe” described in our paper to conduct more experiments to produce strongly magnetized electrons and ions to study the effect of magnetization on the properties of transportation.”
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A. Bose et al, Effect of strongly magnetized electrons and ions on heat flux and symmetry of inertial fusion implosions, Physical examination letters (2022). DOI: 10.1103/PhysRevLett.128.195002
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