Simulation of the cometlike electrostatic noise in the plasma tail of the Space Shuttle

Summary form only given. One of the surprising observations of the STS-3 and Spacelab-2 Shuttle missions was the high degree of wave turbulence in the ambient plasma compared to what was observed from similar instruments flown on unmanned vehicles. The wave turbulence detected in Plasma Diagnostic Package (PDP) experiments is interpreted in terms of the excitation of the beam-arc plasma instability. PIC (particle-in-cell) code simulations have been used to study the instability evolution in the nonlinear regime. Various beam-arc distributions, with azimuthal dependences (in velocity space) corresponding to those expected in the various regions of the Shuttle environment are considered. The output of the simulations show that the instability excites electrostatic waves which propagate in a wide range of directions quasi-perpendicular to the magnetic field. These waves have frequencies close to but slightly above the lower hybrid frequency in the Earth´s frame and are essentially independent of wave number. This is because as the beam-arc plasma instability saturates the waves evolve from the dispersion relation given by linear theory to the dispersion relation of the lower hybrid mode in the ambient plasma. The Doppler shift of the lower hybrid waves can explain most details of the PDP broadband wave spectra.