NASA observations reshape basic plasma wave physics

March 31, 2017 by Mara Johnson-Groh

When NASA's Magnetospheric Multiscale—or MMS—mission was launched, the scientists knew it would answer questions fundamental to the nature of our universe—and MMS hasn't disappointed. A new finding, presented in a paper in Nature Communications, provides observational proof of a 50-year-old theory and reshapes the basic understanding of a type of wave in space known as a kinetic Alfvén wave. The results, which reveal unexpected, small-scale complexities in the wave, are also applicable to nuclear fusion techniques, which rely on minimizing the existence of such waves inside the equipment to trap heat efficiently.

Kinetic Alfvén waves have long been suspected to be transporters in plasmas—a fundamental state of matter composed of charged particles—throughout the universe. But it wasn't until now, with the help of MMS, that scientists have been able to take a closer look at the microphysics of the waves on the relatively small scales where the energy transfer actually happens.

"This is the first time we've been able to see this directly," said Dan Gershman, lead author and MMS scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland in College Park. "We're seeing a more detailed picture of Alfvén waves than anyone's been able to get before."

The waves could be studied on a small scale for the first time because of the unique design of the MMS spacecraft. MMS's four spacecraft fly in a compact 3-D pyramid formation, with just four miles between them—closer than ever achieved before and small enough to fit between two wave peaks. Having multiple spacecraft allowed the scientists to measure precise details about the wave, such as how fast it moved and in what direction it travelled.

Credit: NASA's Goddard Space Flight Center/Genna Duberstein

Previous multi-spacecraft missions flew at much larger separations, which didn't allow them to see the small scales—much like trying to measure the thickness of a piece of paper with a yardstick. MMS's tight flying formation, however, allowed the spacecraft to investigate the shorter wavelengths of kinetic Alfvén waves, instead of glossing over the small-scale effects.

"It's only at these small scales that the waves are able to transfer energy, which is why it's so important to study them," Gershman said.

As kinetic Alfvén waves move through a plasma, electrons traveling at the right speed get trapped in the weak spots of the wave's . Because the field is stronger on either side of such spots, the electrons bounce back and forth as if bordered by two walls, in what is known as a magnetic mirror in the wave. As a result, the electrons aren't distributed evenly throughout: Some areas have a higher density of electrons, and other pockets are left with fewer electrons. Other electrons, which travel too fast or too slow to ride the wave, end up passing energy back and forth with the wave as they jockey to keep up.

In a typical Alfvén wave, the particles (yellow) move freely along the magnetic field lines (blue). Credits: NASA Goddard's Scientific Visualization Studio/Tom Bridgman, data visualizer

The wave's ability to trap particles was predicted more than 50 years ago but hadn't been directly captured with such comprehensive measurements until now. The new results also showed a much higher rate of trapping than expected.

This method of trapping particles also has applications in nuclear fusion technology. Nuclear reactors use magnetic fields to confine plasma in order to extract energy. Current methods are highly inefficient as they require large amounts of energy to power the magnetic field and keep the plasma hot. The new results may offer a better understanding of one process that transports energy through a plasma.

"We can produce, with some effort, these waves in the laboratory to study, but the wave is much smaller than it is in space," said Stewart Prager, plasma scientist at the Princeton Plasma Physics Laboratory in Princeton, New Jersey. "In space, they can measure finer properties that are hard to measure in the laboratory."

In a kinetic Alfvén wave, some particles become trapped in the weak spots of the wave’s magnetic field and ride along with the wave as it moves through space. Credit: NASA Goddard's Scientific Visualization Studio/Tom Bridgman, data visualizer

This work may also teach us more about our sun. Some scientists think kinetic Alfvén waves are key to how the solar wind—the constant outpouring of solar particles that sweeps out into space—is heated to extreme temperatures. The new results provide insight on how that process might work.

Throughout the universe, kinetic Alfvén waves are ubiquitous across magnetic environments, and are even expected to be in the extra-galactic jets of quasars. By studying our near-Earth environment, NASA missions like MMS can make use of a unique, nearby laboratory to understand the physics of magnetic fields across the universe.

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9 comments

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Hat1208
4.6 / 5 (10) Mar 31, 2017
Can't wait to here from the EU crowd how this is good science and point to how if proves them correct but just this science not all the other science that disproves most of what they claim to be the absolute truth that astrophysicists can't understand because they don't understand plasma physics.
gculpex
2 / 5 (4) Mar 31, 2017
Hat, you're still stuck in the 1930's. The world is ever-changing.
cantdrive85
1 / 5 (7) Mar 31, 2017
Hat, see the following from the article;
"A new finding provides observational proof of a 50-year-old theory and reshapes the basic understanding of a type of wave in space known as a kinetic Alfvén wave. The results, which reveal unexpected, small-scale complexities in the wave..."
A 50-year-old theory (proposed by Alfvén, why it's called an Alfvén wave) based upon laboratory experiments RESHAPES THE BASIC UNDERSTANDING, 50-years later... They basically admit to ignoring Alfvén's laboratory research for 50-years in favor of their theoretical beliefs.
These "unexpected" small scale complexities, as well as plasma phenomena which are nearly completely ignored such as double layers, are of profound importance and is the reason astrophysicists are considered plasma ignoramuses. Their MHD models gloss over major fundamental properties of plasma physics. Yes, this is good observational science ILO the typical theoretical thought experiments used by the dark scientists.
Chris_Reeve
1 / 5 (5) Mar 31, 2017
I notice that the article not once directly mention electric current (or electric field) as an aspect of the electromagnetic phenomena. They seem far more interested in waves and magnetic fields -- like when mentioning the jets.

But can a plasma be understood through a process of selecting out the particular aspects which are friendly to the dominant framework?

I'm very skeptical.
691Boat
5 / 5 (9) Mar 31, 2017
I notice that the article not once directly mention electric current (or electric field) as an aspect of the electromagnetic phenomena. They seem far more interested in waves and magnetic fields -- like when mentioning the jets.

But can a plasma be understood through a process of selecting out the particular aspects which are friendly to the dominant framework?

I'm very skeptical.


It's almost like this article is about waves and electrons in magnetic fields, and not electric currents. weird, right? I really wish they would talk about things unrelated to their specific study, too. /sarc
cantdrive85
1.5 / 5 (8) Mar 31, 2017
It's almost like this article is about waves and electrons in magnetic fields, and not electric currents. weird, right? I really wish they would talk about things unrelated to their specific study, too. /sarc

It's almost like this article is about plasma physics;
"In order to understand the phenomena in a certain plasma region, it is necessary to map not only the magnetic but also the electric field and the electric currents." Hannes Alfven
Omitting such primary physics of plasmas is equivalent to describing Earth's climate without considering the atmosphere. Maybe that's why astrophysicists are missing 96% of their Universe.
TheGhostofOtto1923
not rated yet Apr 01, 2017
"are also applicable to nuclear fusion techniques, which rely on minimizing the existence of such waves inside the equipment to trap heat efficiently"

-They are also applicable to storing, manipulating, and transporting materials such as antimatter in plasma form which may well prove to be far more important in the future.
katesisco
not rated yet Apr 01, 2017
As a non-scientist it is hard to follow these 'new discoveries' as they always rename or confuse an existing concept with the 'new discovery.'
IS this the same as solitons that are particles in a quantum description? These are described as speeding up to s.o.l. before disintegrating in a crowed quantum environment. Is this the process that takes the injected energy to the rim before it can actually be used to force fusion at the center?
I realized the necessity of fusion as we have fission plants waiting to destroy life on Earth so we will continue to belabor the 'discovery' of fusion even tho it will never happen.
691Boat
5 / 5 (4) Apr 03, 2017
It's almost like this article is about plasma physics;
"In order to understand the phenomena in a certain plasma region, it is necessary to map not only the magnetic but also the electric field and the electric currents." Hannes Alfven
Omitting such primary physics of plasmas is equivalent to describing Earth's climate without considering the atmosphere. Maybe that's why astrophysicists are missing 96% of their Universe.

Then please enlighten the crowd as to the impact the electric field and electric currents have on these electrons in the article. I am assuming since you brought it up that you clearly have knowledge and evidence as to how their findings are wrong or incomplete because they didn't specifically mention the electric field. Thanks in advance!

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