Nav: Home

Table top plasma gets wind of solar turbulence

June 30, 2017

Turbulent magnetic field dynamics that explain astrophysical phenomena like the evolution of stars could thus far be obtained only through observations via telescopes and satellites. Now a team of scientists from India and Portugal have recreated such magnetic turbulence on a table top in the lab, using a high intensity ultrashort laser pulse to excite a hot, dense plasma on a solid surface and followed the extremely fast evolution of the giant magnetic field generated by the plasma dynamics. This ground-breaking study will be published in Nature Communications on 30 June.

Turbulence is everywhere- from tea cups to tokomaks and from water jets to weather systems, it is something we all see and experience. Yet, even after centuries of serious scientific study, fluid turbulence is still not properly understood and remains "Interesting. Vexing. Longstanding. Unsolved."[1]. While it is difficult to define turbulence simply, it has many recognizable features, the most common being the fluctuations in parameters like velocity and pressure, indicating randomization of the flow [2]. By the way, turbulence is not all bad and destructive as you might feel when tossed around on a flight during bad weather. One good feature is that it enables much faster mixing than possible only with normal, slow diffusion. For instance, the sugar you added in your cup of tea this morning would have taken hours and days to disperse but for your stirring which caused your tea to become turbulent. As you have surely noticed, you stirred the tea in a large circle, but the swirling spread to smaller and smaller lengths and eventually, the mixing occurred at the molecular level. The end result? Even the smallest drop of tea is as sweet as a large gulp! Turbulence also helps in mixing fuel and oxygen for efficient combustion in engines.

Much of our universe is of course not an ordinary fluid but consists of highly ionized gas known as plasma and this plasma can often be extremely hot and swirling at unimaginable speeds. Turbulence in a plasma is much more complex than that in neutral hydrodynamic fluids. In a charged plasma environment, the negatively charged, light electrons and positive heavy ions respond at vastly different length and time scales. The motion of these charged species is governed by electromagnetic forces and the current flow through the charge particle dynamics leads to magnetic field generation. Therefore the randomness of magnetic fields often mimics the fluid turbulence in plasmas.

The team of scientists leading this new study, at the Tata Institute of Fundamental Research, Mumbai, Institute of Plasma Research, Gandhinagar (both in India) and at the Instituto Superior Tecnico, Universidade de Lisboa, Portugal find that the turbulence in the magnetic field is initially driven by the electrons (at a trillionth of a second) and the ions step in and take over at longer times. This is the first time such a 'relay race' involving two different species has been glimpsed. Further, these lab observations have an uncanny resemblance to the satellite data on the magnetic field spectra measured for turbulent astrophysical plasmas in the solar wind, solar photosphere and earth's magnetosheath. Although in the laser experiment the electrons in the plasma get energised initially, the ion dominant response that kicks in at later times shows spectral features similar to those in the astro systems. These experiments thus establish clear connections between the two scenarios, even though the driver of turbulence in the lab plasma is very different from that in the astrophysical system.

Now that we have got wind of solar turbulence on a table top, can we use lab experiments to turn the tables on the intractable problem of turbulence? Well, that may still be a long way off but it is a tantalising prospect that reliable measurements in the lab might make us better and better at peeking into turbulent stellar scenarios.

And that should set off stars in our eyes!

[1] L.P. Kadanoff, Physics Today, Vol. 48, no.9, p11 (1995)
[2] K.R. Sreenivasan, McGraw-Hill Encyclopaedia of Science and Technology, 10th Edn., Vol. 18, p725.
[3] G. Chatterjee et al., Nature Communications, 10.1038/NCOMMS15970 (2017)

Tata Institute of Fundamental Research

Related Evolution Articles:

Prebiotic evolution: Hairpins help each other out
The evolution of cells and organisms is thought to have been preceded by a phase in which informational molecules like DNA could be replicated selectively.
How to be a winner in the game of evolution
A new study by University of Arizona biologists helps explain why different groups of animals differ dramatically in their number of species, and how this is related to differences in their body forms and ways of life.
The galloping evolution in seahorses
A genome project, comprising six evolutionary biologists from Professor Axel Meyer's research team from Konstanz and researchers from China and Singapore, sequenced and analyzed the genome of the tiger tail seahorse.
Fast evolution affects everyone, everywhere
Rapid evolution of other species happens all around us all the time -- and many of the most extreme examples are associated with human influences.
Landscape evolution and hazards
Landscapes are formed by a combination of uplift and erosion.
More Evolution News and Evolution Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#534 Bacteria are Coming for Your OJ
What makes breakfast, breakfast? Well, according to every movie and TV show we've ever seen, a big glass of orange juice is basically required. But our morning grapefruit might be in danger. Why? Citrus greening, a bacteria carried by a bug, has infected 90% of the citrus groves in Florida. It's coming for your OJ. We'll talk with University of Maryland plant virologist Anne Simon about ways to stop the citrus killer, and with science writer and journalist Maryn McKenna about why throwing antibiotics at the problem is probably not the solution. Related links: A Review of the Citrus Greening...