Physicists study Earth’s magnetosphere at UCLA’s Basic Plasma Science Facility
Physicists conducting research at the Large Plasma Device at UCLA’s Basic Plasma Science Facility have succeeded in recreating in miniature the magnetic fields that surround the Earth and other planets — research that may well provide insights into how space weather affects satellites.
A magnetosphere forms around any magnetized object, such as a planet, that is immersed within a stream of ionized gas, called plasma. Because the Earth possesses a magnetic field, the planet is surrounded by a large magnetosphere that extends out into space, blocking lethal cosmic rays and particles from the sun and stars, and allows life itself to exist.
Lead author Derek Schaeffer, a UCLA assistant project scientist and Princeton University associate research scholar, and colleagues report a method to study tiny magnetospheres — sometimes just millimeters thick — in the laboratory. The research is published in the journal Physics of Plasmas and supported by the National Science Foundation.
These mini-magnetospheres have been observed around comets and near certain regions of the moon and have been proposed to propel spacecraft. They are very useful for studying larger planet-sized magnetospheres.
Previous laboratory experiments have been carried out utilizing plasma wind tunnels or high-energy lasers to create mini-magnetospheres. However, these earlier experiments were limited and were not able to capture the full three-dimensional behavior scientists need to understand.
“To overcome these limitations, we have developed a new experimental platform to study mini-magnetospheres on the Large Plasma Device (LAPD) at UCLA,” Schaeffer said. The UCLA facility is a national collaborative research site supported jointly by the U.S. Department of Energy and National Science Foundation.
This platform combines the magnetic field of the LAPD with a fast laser-driven plasma and a current-driven “dipole magnet,” he said.
The LAPD magnetic field provides a model of the solar system’s interplanetary magnetic field, while the laser-driven plasma models the solar wind and the dipole magnet provides a model for the Earth’s inherent magnetic field. Motorized probes allow system scans in three dimensions by combining data from tens of thousands of laser shots.
One advantage to using this setup is that the magnetic field and other parameters can be carefully varied and controlled.
If the dipole magnet is switched off, all signs of a magnetosphere disappear. When the magnetic field of the dipole is switched on, a magnetopause can be detected, which is key evidence of the formation of a magnetosphere.
A magnetopause is the place in the magnetosphere where pressure from the planetary magnetic field is exactly balanced by the solar wind. The new experiments revealed that as the dipole magnetic field is increased, the magnetopause gets larger and stronger.
The effect on the magnetopause was predicted by computer simulations, which were conducted by the researchers to more fully understand and validate their experimental results. These simulations will also guide future experiments, including studies utilizing a cathode recently installed on the LAPD.
“The new cathode will enable faster plasma flows, which in turn will allow us to study the bow shocks observed around many planets,” Schaeffer said.
Other experiments will study magnetic reconnection, an important process in the Earth’s magnetosphere in which magnetic fields annihilate to release tremendous energy.
Caption for image: The Large Plasma Device at UCLA’s Basic Plasma Science Facility.
Credit: Basic Plasma Science Facility, UCLA