New laser technique reveals how plasma instabilities can spaghettify electrons

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Transverse probe image from the experiment showing electron filaments forming.

Transverse probe image from the experiment.

JAI researchers have shown how self-generated magnetic fields in plasma systems generate string-like filaments of electrons.

Across the universe, high-energy particles often travel through a state of matter called plasma, a hot soup of ions and electrons.   Surprisingly, even when the plasma and charged particles start out evenly spread, self-generated magnetic fields turn the system into spaghetti, forcing the charged particles into string-like filaments.  This effect is called the Weibel-like current filamentation instability.  It can cause serious problems for experiments in plasma-based accelerators or some methods for fusion energy methods, but it is incredibly difficult to directly observe in a lab.  

For the first time, researchers from Imperial College London and collaborators from Stony Brook University and Brookhaven National Laboratory carefully studied this phenomenon in the laboratory with precise control over the plasma properties.  They achieved this using a unique set of lasers at the Accelerator Test Facility at Brookhaven National Laboratory.  This facility has a short pulse carbon dioxide laser which is so powerful that it can accelerate to near the speed of light over a distance smaller than the width of a human hair.  What makes this laser special is that the laser emits long-wave infrared light, which means that it gets absorbed even in relatively low-density plasmas, conditions in which the filamentation instability is likely to grow.  

They used this laser to generate electrons and then used a separate optical laser to look at what happened to the plasma that those electrons went through.  The electrons were clearly being turned into thin filaments inside the plasma.  By adjusting the density of the plasma, they saw the size of the filaments change, just as theoretical models predicted.  

This breakthrough opens up opportunities to investigate this instability in detail and allow scientists to work out how to control it when designing next-generation particle accelerators and novel fusion reactors.    

This work is published in Physical Review Letters https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.025102


Reporters

Michael Backhouse

Michael Backhouse
Department of Physics

Nicholas Dover

Nicholas Dover
Department of Physics

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Tel: +44 (0)20 7594 3791
Email: nicholas.dover08@imperial.ac.uk

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