Scientists at a US government plasma lab have discovered a missing component in nuclear fusion equations that could speed the development of a working reactor.
Specifically, the discovery could improve the design of doughnut-shaped fusion reactors known as tokamaks.
Nuclear fusion is the process of fusing two atomic nuclei together to form a single larger nucleus while releasing energy in the process. It’s the same process that powers our sun, where hydrogen atoms are fused together to form helium.
Scientists have been working on nuclear fusion reactors for decades because fusion promises to be a clean, safe and virtually limitless source of energy. However, scientists have yet to arrive at a stable reaction that gives out more energy than it consumes.
Tokamaks work by creating a material called plasma, in which an element – usually hydrogen – is heated so much that it becomes an electrically charged soup of electrons and atomic nuclei. Powerful magnets then contain this plasma in a safe and stable flux, creating conditions where fusion should be possible.
In order to perfect tokamak designs, scientists use computer models to predict how plasma will act under certain conditions. Today, scientists at the Princeton Plasma Physics Laboratory (PPPL), a US Department of Energy lab run by Princeton University, discovered that the equations used to create these computer models were missing an important detail: the resistivity.
Resistivity refers to the ability of any material or substance to prevent the flow of electricity. Just as a rock moves more easily through air than through water, electricity moves more easily through some things than others.
In one study, PPPL scientists found that resistivity is an important property of plasma because it can cause instabilities known as edge-localized modes (ELMs), which are essentially small flares of plasma. If left unchecked, these eruptions could damage fusion reactors, meaning they would have to be taken offline more often for repairs.
“We need to trust that the plasma from these future facilities will be stable without having to build large-scale prototypes, which is prohibitively expensive and time-consuming,” PPPL researcher Nathaniel Ferraro said in a press release. “In the case of edge-localized modes and certain other phenomena, failure to stabilize the plasma could lead to damage or reduced component life in these installations, so getting it right is very important. .”
This is where computer models come in. By adjusting the models to incorporate resistivity, Ferraro and his colleagues, including the study’s lead author and PPPL researcher Andreas Kleiner, found that the models more accurately predicted observations.
Having accurate computer models is important because it means scientists can use time and money as efficiently as possible to build a reactor that they know is likely to perform well, rather than wasting resources on a trial and error approach.
“You want a model that’s simple enough to calculate but comprehensive enough to capture the phenomenon you’re interested in,” Ferraro said. “Andreas discovered that resistivity 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 which specific tokamak properties cause these resistive plasma flares, which could lead to improved designs.
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