Plasma waves near the electron cyclotron frequency in the near-Sun solar wind: implications for inner heliospheric turbulence and the structure of the solar wind

During its first solar encounters, the Parker Solar Probe mission discovered that the near-Sun solar wind is teeming with plasma waves and instabilities. One prominent plasma wave type appears Sunward of 50 solar radii, where intervals of significant plasma wave power near the electron cyclotron frequency (fce) are detected. Most of this wave power is concentrated near 0.7 fce, with strong harmonics extending above fce often observed. At least two distinct concurrent wave modes are identified (electron Bernstein waves and electrostatic whistler-mode waves). Wave intervals range in duration from a few seconds to hours. The amplitude and occurrence of these near-fce waves increases significantly with decreasing distance to the Sun, suggesting that they play an important role in the evolution of electron populations in the near-Sun plasma environment. Correlations are observed between the occurrence of these waves and properties of the population of electrons escaping the solar corona (the strahl), implying that these waves play a role in regulating the heat flux carried by these electrons. Finally, the occurrence of these near-fce waves is strongly correlated with specific solar wind magnetic field configurations and the level of magnetic turbulence at the location of the spacecraft, offering new insight into the macro-scale structure of the near-Sun solar wind.