Electromagnetic fluctuations near the electron plasma frequency from an electron/electron instability

Enhanced electromagnetic fluctuations near the electron plasma frequency om ega(e) are observed in the auroral and polar regions of the terrestrial mag netosphere; until recently, their origin has not been understood. Linear Vl asov theory and a particle-in-cell simulation with a two-dimensional fully relativistic electromagnetic code have been carried out for an electron/ele ctron instability in a homogeneous, collisionless, mag magnetized plasma mo del under the condition omega(e)/\Omega(e)\ < 1 where Omega(e) is the elect ron cyclotron frequency. At propagation parallel to the background magnetic field the instability is strictly electrostatic, but at oblique propagatio n significant electromagnetic fluctuations are also excited. The simulation reproduces the following essential features of the observed plasma frequen cy fluctuations: (1) narrowband frequencies near omega(e), (2) relatively l arge electric fields (delta E/delta B much greater than 1), and (3) episode s of both right-hand and left-hand polarization. This polarization result i s new and has not been published before. Furthermore, the present theory an d simulation show that the right-hand polarized fluctuations are on a short -wavelength beam mode and are excited by linear instability,growth; the lef t-hand fluctuations are at relatively long wavelengths and are apparently d riven by nonlinear processes.