Weakly turbulent plasma processes leading to plasma emission in the presence of a ring-beam electron population

Abstract

The time evolution of the beam-plasma instability and the ensuing emission of transverse waves is studied using a set of self-consistent equations of weak turbulence theory, considering that the electron beam is along a direction with a finite pitch angle relative to the direction of the ambient magnetic field, therefore characterizing a ring-beam electron velocity distribution. The results obtained show that the finite beam pitch angle leads to an enlarged plateau in the beam region of the electron velocity distribution, and to a more complex structure in the spectra of Langmuir and ion-sound waves than obtained with beams with zero pitch angle. The associated turbulence in the spectrum of ion-sound waves is increased in the case of beams with finite pitch angle, in comparison with the case of beams with same speed and zero pitch angle. The spectrum of transverse waves generated by nonlinear processes has similar characteristics for all values of beam pitch angle, but it is observed that the emission at harmonics of the fundamental frequency is higher for moderate values of beam pitch angle than in the case of beam traveling along the parallel direction.