Numerical study of the upstream wave excitation mechanism. I - Nonlinear phase bunching of beam ions
By means of particle simulation, a study is conducted of the excitation mechanism of low-frequency (0.01-0.05 Hz) upstream hydromagnetic waves. Initially, excitation is observed of the right-hand polarized waves propagating parallel to the field-aligned ion beam, which is given as the free energy source. In the nonlinear stage the phase space bunching of beam ions by the excited waves is observed. This bunching effect is applied for the explanation of 'gyrophased bunched' ions observed in the foreshock region.