Of Popular Mechanics
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New Research Explores What Causes a Wave Wave Called “Squeak” in Plasma tokamaks.
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The same laboratory is studying ways to combat the effects of squeaks, such as radio waves.
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Squeaks are caused by changes in the frequency of the waves when the particles rotate outside the plasma center.
Researchers from the Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have released a new document documenting a way to help enable nuclear fusion reactors. They describe the scientific reasons for a phenomenon within the tokamak reactors called screeching in Alfvén mode.
Let’s review some terms here. A tokamak is the great donut-shaped hope of nuclear fusion. (Its cousin, the stellarator, has great potential, but is less developed so far.) Inside, an unfathomably hot plasma stream, as hot or even much hotter than our sun, is contained by a powerful magnetic field that must be fully effective for the reactor to remain at productive melting temperatures.
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There is a constant pressure between the plasma stream and the magnetic field, and the nature of burning hot matter means that the plasma rotates and circulates even within the stream. This is where and why the “chirp” occurs. Researcher Vinicius Duarte explains it in a PPPL statement:
“For any fusion device to work, you need to make sure that the highly energetic particles inside it are very well confined within the plasma core. If those particles move to the edge of the plasma, you can’t keep combustion in the plasma steady state. necessary to make fusion-powered electricity a reality. “
Think of the plasma stream using an analogy that feels outlandish in 2020 socially distant. A stream of people walks in unison, perhaps out of a crowded commuter train and through a station. The fastest people probably follow each other in a narrow strip, and the slowest people are pushed aside.
If one of the fast people kept traveling at exactly the same speed but made a sudden left turn, it would interrupt all the other “lanes” of people who keep moving forward. And the build-up would slow down the entire flow as people started to dodge the obstacle almost immediately. (Fish and birds have an apparently supernatural ability to flow together in changing terrain, but people are surprisingly good at it.)
This is the situation in a tokamak when a chirp occurs. The most highly charged and powerful particles move out of their primary current and cause harmonic disruption to the plasma around them. To study it, the PPPL researchers performed simulations. “The simulations showed that the chirp begins when the rapidly moving particles in the nucleus interact with the waves that ripple through the plasma and spontaneously form groups that migrate to the edge of the plasma,” they report.
PPPL is also exploring ways to use radio waves to help stabilize tokamaks, because radio waves have shown signs of spreading rapidly moving “clumps” to the edge and can disrupt plasma flow or even damage the tokamak. . In this recently published research, PPPL looks at squeaks in depth, using the factors that cause squeak as a hook to continue trying to solve the clusters. Of the report:
“We found a mechanism that allows for a rapid and repeated chirp with a strong amplitude variation in each chirp. Each chirp is associated with a low magnitude shock and local manipulation of the density gradients through a phase change of mode. “
As the high-powered particles hit the plasma stream, they interrupt and reduce the waves around them, changing the general harmonics in the tokamak.
And for the first time, scientists have a simulation tool that they can use to navigate exactly what is happening. “In a sense, it’s like building a microscope,” said researcher Roscoe White.
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