Specifically, the discovery could improve the design of donut-shaped fusion reactors known as tokamaks.
Nuclear fusion is the process of joining two atomic nuclei together to form one larger nucleus with energy released in the process. It’s the same process that powers our sun, where hydrogen atoms fuse together to form helium.
Scientists have worked on nuclear fusion reactors for decades since fusion promised to be a clean, safe, nearly unlimited source of energy. However, scientists have yet to achieve a stable reaction that gives more energy than it consumes.
Tokamex works by forming a substance known as a plasma, in which an element – usually hydrogen – is heated so much that it becomes an electrically charged soup of electrons and atomic nuclei. The powerful magnets then contain this plasma in a safe and stable flow, creating conditions where fusion is possible.
In order to perfect the tokamak designs, scientists use computer models to predict how the plasma will function under certain conditions. Now, scientists at the Princeton Plasma Physics Laboratory (PPPL), a US Department of Energy laboratory operated by Princeton University, have found that the equations used to create these computer models are missing an important detail — the resistance.
Resistance refers to the ability of a substance or material to block the flow of electricity. Just as rocks move more easily through air than water, electricity moves through some objects more easily than others.
In a study, PPPL scientists found that resistance is an important property of plasmas because it can cause instability known as local edge modes (ELMs), which are essentially small revolutions of the plasma. If left unchecked, these explosions can damage the fusion reactors which means they will need to be disconnected more times for repairs.
“We need to have confidence that the plasma at these future facilities will be stable without having to build full-scale prototypes, which is very expensive and time-consuming,” PPPL researcher Nathaniel Ferraro said in a press release. “In the case of edge setting modes and some other phenomena, failure to stabilize the plasma can damage or reduce the life of components in these facilities, so it is very important to correct it.”
This is where computer models come in. By modifying the models to include resistive resistance, Ferraro and colleagues, including study lead author and PPPL researcher Andreas Kleiner, found that the models predicted the observations more accurately.
Having accurate computer models is important, because it means that scientists can use time and money as efficiently as possible to build a reactor they know will likely run well, rather than wasting resources on a trial and error approach.
“You want a model that is simple enough to compute but complete enough to capture the phenomenon you’re interested in,” Ferraro said. “Andreas found that resistance is one of the physical effects that we should include in our models.”
The PPPL study was published in the journal nuclear fusion in May.
Future research will investigate the specific properties of the tokamak that cause resistive plasma eruptions, which may lead to improved designs.
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