Launching Alfvén waves into Earth’s magnetosphere can save satellites from nuclear catastrophe

In 1962, the United States conducted the Starfish Prime test, a megaton-scale hydrogen bomb explosion 250 miles in the sky in Earth’s magnetosphere. Megavolt-energy electrons were trapped in Earth’s radiation belt for years, bouncing back and forth between the north and south poles. In an equivalent disaster today, the particles would wipe out all low-orbit satellites, crippling the internet and many communication systems in a matter of weeks.

“If this happens, how can you sweep all the particles away?” asked Walter Gekelman, an author on a new paper by Gekelman et al. introducing an efficient way to get rid of the trapped electrons.

Previously, the researchers had shown transmitting Alfvén waves into plasmas is effective in reducing electron flux. In their paper, they created a wire loop antenna with a low oscillating current to launch these waves. By inserting a ferrite core into the device, they were able to create the waves more cheaply and efficiently, decreasing antenna energy usage by a factor of over 300 when compared to a traditional, ceramic-core antenna. Multiple antennas can be used simultaneously to modulate the Alfvén wave’s wavelength.

The researchers tested several antennas at UCLA’s Large Plasma Device. They trapped a ring of high-energy electrons in a magnetic mirror and injected Alfvén waves into the system using a rotating magnetic field antenna at higher power. They found it destroyed the electron ring.

Applications of this work are not limited to human-caused nuclear catastrophes. Coronal mass ejections can have a similar effect on Earth’s magnetosphere. The shape of the Alfvén wave is also affected by the magnetic field it is in, so the group is studying more complicated wave topologies using different antenna configurations.

Source: “Ferrite based antennae for launching Alfvén waves,” by W. Gekelman, P. Pribyl, S. Vincena, S. W. Tang, and K. Papadopoulos, Review of Scientific Instruments (2019). The article can be accessed at https://doi.org/10.1063/1.5103171 .