Transformation of space-charge wave to electromagnetic wave in active space experiments
主动空间试验中空间电荷波向电磁波的转换

We have analyzed the transformation from the space-charge wave into the electromagnetic wave when electron beams pass through the concentration step of cold anisotropic plasma along the geomagnetic field. We focus our analysis on several typical conditions such as weak magnetic field approximation, whistler wave excitation, and low frequency approximation. We first derive the dispersion relation and the wave number of the space-charge wave under small signal assumption, and then calculate the amplitude of the wave excitation in the concentration step of the plasma, using the electromagnetic component and the boundary condition of the velocity of the electron beam. We obtain the approximate solution to the coefficient of the transformation from the space-charge wave into the electromagnetic wave, and provide the Poynting vector presentation of the corresponding wave radiation. We have demonstrated the principle possibility of the Alfven wave and Whistler wave excitation in inhomogeneous plasma by the modulated electron beam with transition radiation mechanism. These results can be used to analyze experimental data collected in active plasma experiments in space.