Magnetized plasmas with a twist

recent paper by J. T. Mendonça and J. P. Bizarro [1] was selected for the highlights section of this month’s Europhysics News, the magazine of the European Physical Society [2]. In their work, the authors explore the properties of twisted light beams inside a magnetized plasma.

Twisted waves are light waves that carry angular orbital momentum (OAM), and whose wavefront spins as the wavepropagates. In plasma physics and many other areas, the study of twisted waves in general, and twisted laser beams in particular, has received considerable attention in recent years, leading to a number of new and unexpected effects.

Mendonça and Bizarro have focused on the case of a twisted wave propagating in a magnetoplasma, finding a variety of solutions and providing a wave-kinetic description. They realized that such waves can be described as quasi-particles carrying an intrinsic OAM. They have also introduced a generalized concept of plasma turbulence, consisting of a gas of several types of such twisted quasi-particles.

As an example of an application, the authors have considered a single wave beam with no OAM propagating in a plasma, in the presence of a magnetic field, showing that shower of higher order OAM modes is generated.

This new result will allow the extension to magnetised plasmas of previously identified applications for twisted waves, such as possible new configurations for electron and positron acceleration, laser-target interactions, or the amplification of laser pulses to high intensities via Raman and Brillouin decay. 

The work also established a wave-kinetic equation, describing the exchange of orbital-angular momentum between different modes in a turbulent plasma.

1. J. T. Mendonça and J. P. S. Bizarro, 'Twisted waves in a magnetized plasma', Plasma Phys. Control. Fusion 59, 054003 (2017); doi: 10.1088/1361-6587/aa6231