Electron heating by nonlinear whistler waves

Nonlinear whistler-mode phenomena observed in laboratory plasmas will be addressed. Nonlinearities arise when strong waves modify the density, temperature and magnetic field, all of which affect the wave propagation. A brief review of thermal filamentation will be given. The main focus is on the magnetic nonlinearity of whistler modes whose wave magnetic fields exceed the ambient magnetic field B0. Such intense waves are launched from loop antennae with axial fields alongB0 and form in one polarity whistler spheromaks and whistler mirrors in the opposite polarity. Spheromaks propagate slower, mirrors faster than linear whistlers. Spheromaks show soliton-like properties. In a whistler vortex (spheromak), the toroidal electron current ring with J‖E converts magnetic energy into electron heat. In contrast, linear whistlers and whistler mirrors are supported by electron Hall currents and produce negligible heat (J · E = 0). The collision of counter-propagating spheromaks is inelastic, forming a stationary, helicity-free field-reversed configuration, while linear whistler modes pass through each other without interaction. These results are important for the understanding of strong whistler turbulence and reconnection.