Effects of anisotropy of beam temperature on Langmuir and transverse wave spectra generated by beam–plasma instability

Understanding the dynamics of beam–plasma interaction is key to understanding solar radio bursts of types II and III. Most of the numerical work done on the topic assumes a beam that is isotropic in temperature. As we are not aware of any fundamental reason for that assumption, in this work, we analyze the effect that beam temperature anisotropy has on the dynamics of the beam-plasma system, assuming a two-dimensional geometry. The numerical results obtained show that the increase in the beam parallel temperature leads to a decrease in the Langmuir wave emission, and are corroborated by an analytical description of the relationship between beam parallel temperature and Langmuir wave intensity. We also investigate the effect of temperature anisotropy on electromagnetic waves generated by the nonlinear dynamics, and obtain that the change of the beam parallel temperature affects the intensity for both the fundamental and harmonic emissions, with a more pronounced effect for harmonic emission.