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Data from the first two orbits of the Sun by Parker Solar Probe reveal thatthe solar wind sunward of 50 solar radii is replete with plasma waves andinstabilities. One of the most prominent plasma wave power enhancements in thisregion appears near the electron cyclotron frequency (f_ce). Most of this wavepower is concentrated in electric field fluctuations near 0.7 f_ce and f_ce,with strong harmonics of both frequencies extending above f_ce. At least twodistinct, often concurrent, wave modes are observed, preliminarily identifiedas electrostatic whistler-mode waves and electron Bernstein waves. Waveintervals range in duration from a few seconds to hours. Both the amplitudesand number of detections of these near-f_ce waves increase significantly withdecreasing distance to the Sun, suggesting that they play an important role inthe evolution of electron populations in the near-Sun solar wind. Correlationsare found between the detection of these waves and properties of solar windelectron populations, including electron core drift, implying that these wavesplay a role in regulating the heat flux carried by solar wind electrons.Observation of these near-f_ce waves is found to be strongly correlated withnear-radial solar wind magnetic field configurations with low levels ofmagnetic turbulence. A scenario for the growth of these waves is presentedwhich implies that regions of low-turbulence near-radial magnetic field are aprominent feature of solar wind structure near the Sun.

Plasma Waves near the Electron Cyclotron Frequency in the near-Sun Solar Wind