Ion resonances and ELF wave production by an electron beam injected into the ionosphere: Echo 6

Abstract

The interaction with the ionospheric plasma of two separately controllable electron beams injected from the Echo 6 sounding rocket in the auroral zone has been studied using orthogonal electric double probes and other instruments on a separate plasma diagnostics payload. The gun pulses produced a myriad of large electric probe signals covering the entire ion gyro range between dc and 1250 Hz. In particular a signal driven at the 1‐kHz gun frequency and a naturally occurring resonance at 840 Hz near the 799‐Hz proton gyrofrequency were studied. The 1‐kHz signal decreased by a factor of 100 between 45 and 90 m from the beam field line but was detectable in the 1‐mV/m range at 120 m, confirming previous findings that pulsed electron beams may serve as ELF wave sources in space. The 840‐Hz resonance was excited by a beam injected parallel to the magnetic field but could be quenched by the addition of a transverse beam in what appears to be a case of controlled damping. The 840‐Hz and 1‐kHz signals were superposed on large‐amplitude fluctuations and were extracted using power spectral analysis. The data contain a large variety of ion gyro range frequencies which are under study. The paper discusses the interpretation of the electric probe responses and large turbulent payload floating potential effects produced by the hot plasma generated by the beams.