Physics Department Colloquia
Events on Friday, February 25th, 2022
- Magnetic Reconnection, a Celestial Phenomenon in the Laboratory
- Time: 3:30 pm
- Place: 2241 Chamberlin Hall
- Speaker: Jan Egedal and the WiPPL team , UW Madison
- Abstract: The Earth is embedded in the Sun's extended atmosphere, where the Earth's magnetic field acts as a shield against the incoming solar wind plasma. However, this shielding is not perfect. Through the process of magnetic reconnection solar particles can penetrate the magnetosphere and greatly influence the conditions in space that affect the Earth and its technological systems---magnetic reconnection controls space weather. Notable aspects of reconnection include its ability to convert magnetic energy into particle energy while changing the topology of the magnetic field lines. Although reconnection occurs in microscopic diffusion regions, it often governs the macroscopic properties and behavior of the systems. It controls the evolution of explosive events such as solar flares, coronal mass ejections and magnetic storms in the Earth's magnetotail. The latter drives the auroral phenomena.
The phenomenon is explored on the Terrestrial Reconnection Experiment (TREX) at UW-Madison, where the absolute rate of reconnection is set by an external drive. A shock interface between the supersonically driven plasma inflow and a region of magnetic flux pileup permits the normalized reconnection rate to self-regulate to a fixed value. In agreement with numerical and theoretical results, the width of the electron diffusion regions is characterized by the kinetic length scale of the electrons. While the reconnection layers are modulated by a current-driven instability, their characteristics remain consistent with a 3D simulation for which off-diagonal stress in the electron pressure tensor is responsible for fast reconnection.
- Host: Cary Forest