Improving the design of doughnut-shaped fusion facilities could be done with the help of researchers at the U.S. Department of Energy.
Nathaniel Ferraro, one of the collaborating researchers, said that resistance is the property of any substance that impedes the flow of electricity. It's similar to the viscosity of a fluid, which makes it hard for things to move through it. A stone will move slower through molasses than it will through water.
A new way that resistivity can cause instabilities has been found. Predicting the behavior of the soup of electrons and atomic nuclei that makes up 99% of the visible universe can be done with the help of Resistivity.
"We want to use this knowledge to figure out how to develop a model that allows us to plug in certain plasma characteristics and predict whether the plasma will be stable before we actually do an experiment," said the lead author of the paper. He said that the research showed that resistivity mattered and that models should include it.
The sun and stars are powered by fusion, which combines light elements in the form of a charged state of matter. Scientists want to harness fusion on Earth for a very long time.
Scientists want the tokamak to be stable because instabilities can cause eruptions known as edge-localized modes that can damage internal components of the tokamak. Future fusion reactor will have to run for months at a time.
"We need to be confident that the future facilities will be stable without having to build full-scale prototypes, which is expensive and time- consuming," Ferraro said. It's important to get it right in the case of edge-localized modes and other phenomena because they can lead to damage or reduced component lifetimes.
The predictions made by the code for a variety of spherical tokamaks are not always correct. The National Spherical Tokamak Experiment-Upgrade (NSTX-U), a facility that looks like cored apples, is being studied by physicists as a potential design for a fusion pilot plant.
Kleiner and the team used the high-powered computers in the National Energy Research Scientific Computing Center, a DOE Office of Science user facility at Lawrence Berkeley National Laboratory in Berkeley, California, to try and add resistivity to the model.
The head of the Tokamak Experimental Sciences Department said that the data from previous discharges was very important. Experiments showed that the effects were to blame. The improved model could show us how to get rid of the ELMs.
Physicists can use these types of computer models to make fusion machines behave in a way that makes it more likely. A model is a set of mathematical equations.
All models use assumptions. The research uses a model that describes the plasma as a fluid. It's not possible to have a model with all of the physics in it. It would be difficult to figure it out. To capture the phenomenon you are interested in, you need a model that is easy to calculate and complete. One of the physical effects that should be included in our models is resistivity.
Past computations were done by Kleiner and others. It adds to those findings by looking at more discharges produced by the machine preceding the NSTX-U. The research helped the scientists figure out that instabilities are not caused by pressure.
Future research will look at why these types of instabilities happen. We don't know which property causes the mode to appear. Kleiner said that it could be a result of the spherical torus geometry or the plasma's shape. Further simulations are needed to confirm this.
More information: A. Kleiner et al, Critical role of current-driven instabilities for ELMs in NSTX, Nuclear Fusion (2022). DOI: 10.1088/1741-4326/ac64b3
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