# Synopsis: Radiation-Belt Scattering in the Lab

Experiments in a laboratory recreate an interaction between electrons and plasma waves that may be responsible for large electron-flux variability in the Earth’s radiation belts.

The flux of electrons in Earth’s radiation belts can sometimes vary by a factor of $100,000$ in a matter of hours. Space scientists assume that these rapid changes are partly due to the scattering of electrons from so-called whistler-mode waves—plasma waves in the Earth’s magnetosphere with frequencies in the kilohertz range. A first experimental observation of this scattering process, recreated in the lab, is presented in Physical Review Letters.

The Van Allen radiation belts are two donut-shaped regions, in which charged particles spiral along the Earth’s magnetic field lines. The outer belt can vary dramatically, especially during geomagnetic storms. One possible factor contributing to this variation is the resonant interaction of electrons with whistler modes whose frequency matches the electrons’ gyrofrequency. However, verifying this hypothesis has been difficult because the change in the electron trajectory is very small in a laboratory experiment.

Bart Van Compernolle and his colleagues at UCLA have managed to observe electron scattering from whistler waves for the first time. Inside the Large Plasma Device (LAPD) at UCLA, they generated a beam of $5$-kilo-electron-volt electrons, which spiraled along the machine’s magnetic field lines before reaching a detector with a small pin-hole entrance. This hole filtered the incoming electrons depending on the pitch angle of their helical trajectory. The team then induced whistler waves in the LAPD plasma with a radio antenna and observed a drop in the number of electrons making it to the detector. The drop was consistent with the expected change in pitch angle from scattering off of whistler waves. The authors expect this verification should help interpret data coming from satellites, such as the recently launched Van Allen Probes that are studying the Earth’s radiation environment. – Michael Schirber

### Announcements

More Announcements »

## Previous Synopsis

Atomic and Molecular Physics

Complex Systems

## Related Articles

Optics

### Synopsis: Sharper Vision for Infrared Telescopes

Converting infrared light to visible light might boost the sensitivity of infrared telescope arrays. Read More »

Astrophysics

### Focus: More Hints of Exotic Cosmic-Ray Origin

New Space Station data support a straightforward model of cosmic-ray propagation through the Galaxy but also add to previous signs of undiscovered cosmic-ray sources such as dark matter. Read More »

Cosmology

### Viewpoint: Connecting the Bright and Dark Sides of Galaxies

A universal law shows that the rotation of a disk galaxy is determined entirely by the visible matter it contains, even if the disk is mostly filled with dark matter. Read More »