Laboratory generation of broadband ELF waves by inhomogeneous plasma flow

Abstract

AbstractTransversely accelerated ions and the associated heating of the high‐latitude ionosphere have been attributed to broadband extremely low frequency (BBELF) turbulence. Controlled laboratory tests of the hypotheses on the formation mechanism of BBELF waves have involved only a few examples, e.g., current‐driven and shear‐driven instabilities. In this work, electrostatic fluctuations in the ion cyclotron frequency range have been excited by inhomogeneous energy‐density‐driven instability (IEDDI). This was achieved using the interpenetrating plasma method with a much larger electric field scale size LE comparable to the ion gyroradius ρi, which was challenging earlier because of plasma conditions. The peak frequency of the IEDDI spectrum falls as low as ω≈0.3ωci, where ωci is ion cyclotron frequency. This is an interesting result because the previous attempts could not produce such low‐frequency IEDDI, although it was known theoretically to be possible. The observations made by FAST, Freja, and Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites might be explainable in terms of the reported experimental results.