Mimicking The Swirling Of Plasma Across The Cosmos

High-intensity lasers have helped researchers recreate turbulent flows of plasma seen at a planetary scale in the lab.

AsianScientist (July 11, 2017) – Using a table-top laser, researchers have recreated turbulent magnetic fields which previously could only be observed by telescopes and satellites. Their findings, published in Nature Communications, shed light on the movement of plasma at a planetary scale.

Turbulence is everywhere—from tea cups to water jets to weather systems—and it has several recognizable features such as fluctuations in velocity and pressure, indicating randomization of flow. However, fluid turbulence is still not well understood.

Much of our universe is not an ordinary fluid but consists of highly ionized gas known as plasma. 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 positively charges heavy ions respond at vastly different length and time scales. The motion of these charged species is governed by electromagnetic forces, and the flow of current through the charge particle dynamics generates a magnetic field. Therefore the randomness of magnetic fields often mimics the fluid turbulence in plasmas.

In this study, scientists from the Tata Institute of Fundamental Research, Mumbai Institute of Plasma Research, Gandhinagar and the Universidade de Lisboa, Portugal used a high intensity ultra-short 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.

They observed that turbulence in the magnetic field is initially driven by the electrons (at a trillionth of a second), while ions drive turbulence at longer time scales. This is the first time such a ‘relay race’ involving two different species has been glimpsed.

Furthermore, these 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. In the laser experiment, although the electrons in the plasma get energized initially, the ion dominant response that kicks in at later times shows spectral features similar to those in the cosmic systems.

These experiments thus raise the tantalizing prospect that reliable measurements in the lab might make us better at peeking into turbulent stellar scenarios.

The article can be found at: Chatterjee et al. (2017) Magnetic Turbulence in a Table-top Laser-plasma Relevant to Astrophysical Scenarios.


Source: Tata Institute of Fundamental Research; Photo: Shutterstock.
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