Science and engineering education at all levels is a strong element of the lab’s mission.

Plasma in a Jar

With the generous support of BU’s Center for Space Physics and the National Science Foundation (NSF) the team has developed a Planeterrella to show the glowing light of a plasma in a jar.  Although 99% of the observable universe is in a plasma state, it’s rarely observed visually. BU’s Planeterrella is used for demonstrations throughout campus and within the community.

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The violet glow comes from collisions of the plasma with the depleted air in the bell jar. Inside the bell jar a vacuum pump reduces the air pressure to roughly 1/10,000 that of atmospheric pressure. Inside are two metallic sphere’s containing strong permanent magnets. Once the pressure in the jar is lowered, a strong electric field is applied across the metallic spheres. This electric field causes electrons to be ripped off from one sphere (ionized) and accelerated towards the other. Although the bell jar is pumped down to vacuum, some neutral atoms from the air still remain inside, and when the electron collies with the neutral, light is emitted. The plasma interacts with the magnetic field of the sphere in a similar way as to charged particles in the Earth’s magnetic field. This ring of plasma in the jar is similar to the trapped charged particles in the Earth’s radiation belts.

This physical process is the same one that generates the aurora near the northern and southern poles. The Planeterrella at BU is based off of a design conceived by Dr. Jean Lilensten of the Planetary and Astrophysical Institute of Grenoble in France. The work is made possible by the NSF award AGS-1845151.