Nonlinear electron magnetohydrodynamics physics. III. Electron energization

Wave-particle interactions of low-frequency whistler modes with wave magnetic fields exceeding the ambient field are investigated experimentally. These highly nonlinear modes are excited with magnetic loop antennas in a large magnetized afterglow plasma. While the nonlinear wave properties are described elsewhere, the present paper focuses on the modification of the electron distribution function by the whistler waves. When the electron current flows in regions of magnetic nulls, such as in spheromak and field-reversed configurations FRCs , strong electron energization is observed. When the whistler modes are created by electron Hall currents, such as in whistler mirrors, no significant energization occurs. The electron temperature can be raised locally by an order of magnitude. Non-Maxwellian distributions with energetic tail electrons are observed. Electron energization to 10 eV produces visible light emission whose time and space dependence is mapped. The light source travels with the subthermal speed of whistler spheromaks. When counterpropagating spheromaks collide, the resultant FRC produces strong local heating and light which dissipates its free magnetic energy. © 2008 American Institute of Physics. DOI: 10.1063/1.2903070