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.
Synopsis figure
NASA

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


Features

More Features »

Announcements

More Announcements »

Subject Areas

AstrophysicsPlasma Physics

Previous Synopsis

Atomic and Molecular Physics

High-Precision Terahertz Spectroscopy

Read More »

Next Synopsis

Complex Systems

Bird Flocks Shatter on Impact

Read More »

Related Articles

Synopsis: A Reionization Filter for the Cosmic Microwave Background
Cosmology

Synopsis: A Reionization Filter for the Cosmic Microwave Background

A new method of analyzing cosmic microwave background data could isolate signatures from the so-called reionization period that occurred a few hundred million years after the big bang. Read More »

Synopsis: LIGO’s Black Hole Got the Boot
Astrophysics

Synopsis: LIGO’s Black Hole Got the Boot

An analysis of data from LIGO’s second gravitational-wave event indicates that a supernova can impart a strong kick to the black hole it creates. Read More »

Synopsis: Tackling the Small-Scale Crisis
Cosmology

Synopsis: Tackling the Small-Scale Crisis

Precise measurement of the cosmic microwave background could solve a problem of current cosmological models known as the small-scale crisis. Read More »

More Articles