IIT Kanpur researchers revisit 70-year-old plasma relaxation problem in outer space

Cosmological plasmas are plasmas that exist in outer space, such as in stellar envelopes, gaseous nebulae, and interstellar space. Plasmas are a state of matter that consists of charged particles, such as ions and electrons that interact with electromagnetic fields. These plasmas are often dilute, meaning they are not very dense, but they are still important because they play a crucial role in shaping the universe.

A team of researchers from the Indian Institute of Technology Kanpur has proposed a universal mechanism for turbulent relaxation, which can be applied to a wide range of fluids, including plasmas and complex fluids. 

This principle called the principle of vanishing nonlinear transfer (PVNLT), explains how a turbulent system attains a steady, stable state of relaxation when the driving force is switched off. 

The team comprised Prof. Supratik Banerjee, and researchers Arijit Halder, and Nandita Pan, from the Department of Physics, IIT Kanpur.

To illustrate this concept, the researchers use the example of mixing milk in a cup of coffee. “When we stir the coffee, we create eddies and turbulence that cause the milk to mix quickly. However, when we stop stirring, the system organizes itself via "turbulent relaxation" before it finally ceases to flow. According to PVNLT, this happens when the system gets rid of its nonlinear transfers, terminating the turbulent cascade. In this state, stability is ascertained as a scale-dependent entropy function is maximized when the correlation between different parts of the fluid tends to vanish,” said Prof. Supratik Banerjee.

"Through the principle of vanishing nonlinear transfer, we have been able to uncover a universal mechanism for understanding how turbulent systems reach a relaxed and stable state. Our research has important implications not only for the study of fluids but also for plasmas and other complex fluids. We are excited about the potential for future applications of this principle in a wide range of fields,” added Prof. Banerjee.

The PVNLT principle has been shown to give the correct pressure-balanced relaxed states for both two and three-dimensional fluids and plasmas, as previously obtained in numerical simulations. This means the current principle can correctly predict the way the turbulent relaxation happens in reality. This technique is fundamental and can easily be applied to complex fluids, including compressible fluids, plasmas, binary fluids etc.

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