New mechanism in plasma physics discovered

A paper by a team of researchers from IST published in the prestigious journal Physical Review Letters has been selected as Editor’s Suggestion, assigned to articles considered to be particularly important, interesting, and well-written. The lead author, APPLAuSE PhD student Pablo J. Bilbao, conducted the research under the supervision of Professor Luís O. Silva of the Physics Department and GoLP/IPFN. The researchers have discovered a new mechanism in plasma physics that could explain the unknown phenomena underlying radiation emission from astrophysical objects, such as Fast Radio Bursts. Furthermore, the paper suggests that other physical setups could have similar effects, leading to further research in extreme plasma physics in the laboratory.

The momentum distribution of plasma is a mathematical tool used by physicists to understand how the energy of a plasma is distributed among its particles – atoms, ions and electrons. Typically, higher energy particles are less common than lower energy ones. However, this paper shows that by applying strong magnetic fields, extremely hot plasmas will cool down and develop ring-shaped momentum distributions. In other words, the plasma's energy is now distributed differently, with more high-energy particles than low-energy ones. As a result, these plasmas can generate coherent light, similar to how a laser works. Although the existence of such plasmas was previously hypothesized, until now there was no explanation for the formation of the rings.

Classical electrodynamics textbooks tell us that when accelerated in powerful electromagnetic fields, charged particles will radiate. When the particles are relativistic and the fields are strong, the radiation is called synchrotron radiation, in the x-ray region or even higher energies of the electromagnetic spectrum, with many applications across science and technology. If the energy lost by particles via radiation becomes comparable to their kinetic energy, their motion is strongly modified, the particles slow down and are damped by radiation reaction or radiation damping – a phenomenon that has been studied since the 1890s, by Lorentz, and since then by many prominent physicists, including Abraham, von Laue, Born, Pauli, Dirac, and Landau.

Currently, scientists anticipate radiation reaction effects to play a substantial role in plasmas surrounding the magnetosphere of pulsars and magnetars. These celestial objects possess magnetic fields that can exceed 100,000 Teslas, which is over 2,200 times stronger than the most potent continuous magnets ever produced on Earth, with a strength of 45 Teslas. To put this figure in context, suppose we amplified a small fridge magnet with a magnetic field of 0.01 Teslas to the same strength as a pulsar or magnetar. In that case, the little fridge magnet would be capable of lifting 100 metric tons of iron. The latest generation of laboratory experiments with intense lasers also enables the creation of plasmas under such intense electromagnetic fields, making the study of radiation reaction effects on collective plasma dynamics increasingly relevant.

With this new finding, a new avenue of research has been opened. The research team now plans to continue to investigate this novel effect in different scenarios such as laser-plasma laboratory setups and other astrophysical objects.

 To know more:

P. J. Bilbao and L. O. Silva, 'Radiation reaction cooling as a source of anisotropic momentum distributions with inverted populations'