Kinetic modeling of magnetic reconnection in space and astrophysical systems (Chair: PH Diamond)
Seminar Room 1, Newton Institute
The large scale dynamics of magnetized plasma systems are typically modeled with the MHD equations. However, the MHD description typically breaks down at spatial scales where dissipation is required to either break magnetic field lines, allowing reconnection to occur, or to locally dissipate energy. In the case of magnetic reconnection, the Hall MHD model has been found to accurately reproduce the rates of reconnection determined by kinetic modeling, a consequence of the role of dispersive waves in reconnection. However, critical issues in space and astrophysics remain that require a kinetic description and at the same time have significant consequences for the description of the large-scale dynamics of plasma systems. After reviewing the recent kinetic model of fast reconnection, I will focus on two generic topics, electron heating and kinetic scale turbulence and its role in driving reconnection. Nearly half of the magnetic energy released in solar flares is channeled into energetic electrons and recent observations in the magnetosphere confirm that reconnection can directly drive electrons to near relativistic energies. Simulations reveal that reconnection leads to the formation of extended density cavities that map the magnetic separatrices and support a finite parallel electric field. These cavities act as electron accelerators and as a result of multiple passses through these acceleration cavities electrons quickly reach relativistic energies. In boundary layers of the magnetosphere, where large-scale parallel electric fields are expected from modeling, parallel electric fields take the form of intense, spatially-localized, bipolar structures (electron holes) and double-layers. These are manifestly kinetic nonlinear structures where electrons and ions can directly exchange energy with large scale fields. Simulations of reconnection reveal the self-consistent development of these structures, facilitating the exploration of their role in providing the dissipation required to drive reconnection.
- http://www.glue.umd.edu/~drake/ - web site with papers and other information