Observations of Langmuir ponderomotive effects using the Solar TErrestrial RElations Observatory spacecraft as a density probe

Langmuir ponderomotive effects are nonlinear effects that enable to couple the electron and ion dynamics in space plasmas. The main difficulty to provide observational evidence of such nonlinear coupling is to simultaneously observe both fluctuations of plasma density and electric field. We have thus developed a new method to measure and to calibrate in situ small scale density fluctuations. Density fluctuations in the solar wind are measured using the observed quasistatic fluctuations of the STEREO spacecraft floating potential in the frequency range, where the spacecraft floating potential is in quasistatic equilibrium between photoionization and electron attachment, whereas the potential of the antenna, of much longer equilibrium time scale, is blind to the density fluctuations. Density fluctuations and Langmuir waves are thus directly and simultaneously measured using a dataset of more than three years of STEREOWAVES measurements. We present here the first observational evidence for ponderomotive effects in the solar wind that nonlinearly couple density fluctuations to high energy Langmuir waves (( 0 E 2) / (nk B T) 1 0 - 4). © 2011 American Institute of Physics.