When: 
Friday, December 1, 2017 - 3:30pm - 4:30pm
Where: 
Hugel Science Center 100
Presenter: 
James Schroeder (University of Iowa)
Price: 
Free

Please join the Physics Department for a colloquium by Jim Schroeder, University of Iowa, on "Clear with a chance of electron precipitation."  There will be tea at 3:10 in the lobby of the Hugel Science Center, followed by the talk at 3:30.

Motivation: Auroras form only 100-400 km overhead and are the culmination of events beginning at the sun. Determining the processes that cause auroras is an important part of understanding Earth’s interaction with its space environment. While auroras have drawn the attention of humankind for millennia, the last half-century of rocket and satellite-borne experiments have revolutionized our understanding of auroral formation. The solar wind, a diffuse gas of ions and electrons in the plasma state of matter, emanates from the sun and interacts with Earth’s magnetic field. Electrons are guided along Earth’s magnetic field lines, precipitate onto the upper atmosphere, and collide with neutral atoms. These collisions cause atomic excitations that relax and give off the photons that make up auroras. However, the cause of electron precipitation is debated. A growing body of satellite data indicates that plasma waves around Earth can accelerate electrons and cause them to precipitate. One of the primary waves suspected in this process is the Alfvén wave. Even though satellites fly directly through auroras, determining definitively if Alfvén waves cause electron precipitation has not been possible because of the complexity of the environment. Laboratory experiments avoid many of these complexities and may be the best approach for testing the interaction of Alfvén waves and electrons.

My research: The extra control of a laboratory experiment is used to study electron interactions with Alfvén waves. Experiments are performed in the Large Plasma Device, a shared facility at UCLA. Alfvén waves are launched using a new high-power antenna. Alfvén wave interactions with electrons are recorded by a novel diagnostic that measures the electron velocity distribution using the absorption of gigahertz frequency waves. Recent results have shown for the first time that Alfvén waves accelerate electrons, and a solution to the Boltzmann equation accurately describes these measurements. Ongoing experiments are exploring the net transfer of energy to electrons to see if Alfvén waves are capable to producing auroras.

 

 

Sponsored by: 
Physics Department

Contact information

Name: 
David Nice
Phone: 
x5204
Email: 
niced@lafayette.edu