ELECTRIC-FIELD MEASUREMENTS DURING SUPERCHARGING EVENTS ON THE MAIMIK ROCKET EXPERIMENT

We report on the observation and analysis of quasi-DC electric fields measured during active electron emission from the MAIMIK sounding rocket. The MAIMIK mother-daughter tethered rocket consisted of two separately instrumented payload sections which were detached in-flight. The daughter payload included a variable current, 8-keV electron accelerator and instrumentation to measure the vehicle potential relative to the ionospheric plasma. The electric field detector was part of the quiescent mother payload which separated from the daughter at a constant speed. Of particular interest to the present study were the observations of impulsive electric fields measured at the initiation of the beam for emission currents which drove the daughter payload into an overcharged state. At locations well removed from the active payload the electric field signature consisted of a 1- to 2-ms, monopolar impulse field that had a rapid risetime and a more gradual decay. The components of the vector field were examined using a cylindrical coordinate system that placed the active payload at the origin and fixed the azimuthal injection angle of the beam. In general, the radial components of the field were directed out from the positively charged central body and presumed to be of electrostatic origin. The tangential components had consistent positive deflections indicating that these field components were mostly electromagnetic in nature. We suggest that the measured impulse fields were due to a shielded ion blast wave propagating away from the highly charged central body with azimuthal asymmetries created by the distribution of space charge associated with a virtual cathode and escaping beam electrons. The time-varying electrostatic fields drove transient Hall currents that were carried by cold electrons E x B drifting near the head of the blast wave.