Electric Field, Magnetic Field, and Density Measurements on the Active Plasma Experiment

摘要

High-resolution, in situ measurements of dc and wave electric fields, magnetic fields, and plasma number density have been gathered by instruments on a diagnostic payload at which a high-velocity, overdense aluminum ion beam was directed from a separate payload spaced 468 m away. The experiment, called the Active Plasma Physics Experiment, was carried out in the Earth's high-latitude ionosphere at 360-km altitude using a sounding rocket. The experimental data clearly show a large diamagnetic cavity with a 93% depletion of the Earth's magnetic field within a narrowly confined (<500-m) ion beam whose number density exceeded 10~9 cm~(-3). Associated with the release, dc electric fields with amplitudes >1.5 V/m perpendicular to the magnetic field were observed that represented both the E x B bulk plasma velocity and a magnetosonic wave, which preceded the arrival of the beam that was also evident in the ΔB magnetometer data. The electric field data also show the presence of electric fields parallel to the magnetic field, including a bipolar electric field signature presumably set up to ensure current continuity. Other plasma waves associated with the release include Alfven perturbations, intense broadband turbulence extending to frequencies beyond 1 MHz, whistler-mode electromagnetic emissions at the ambient O~+ lower hybrid frequency, and ion acoustic turbulence. The measurements provide a self-consistent picture of the electrodynamics surrounding a high-velocity, overdense ion beam released in the high-latitude ionosphere.