Electromagnetic ion beam instabilities: Oblique pulsations

We present results of a two-dimensional hybrid simulation of the electromag netic proton beam instability. We show that for a case of cold and rather h igh density proton beam the oblique right-handed resonant modes play an imp ortant role. The interaction of these modes with the beam protons causes si gnificant beam density fluctuations. At the nonlinear stage the oblique mod es give rise to a beam filamentation. Beam filaments influence strongly the evolution of the instability. They create pulses of a strong magnetic fiel d. These pulses share some properties of the magnetic pulsations (short, la rge-amplitude magnetic structures). We suppose that the oblique modes play an important role in the structure of the quasi-parallel Earth's bow shock.