Spectral characterstics of fluctuations in laboratory plasma simulating features of bottom side of equatorial spread‐F

Spectral characteristics of fluctuations in laboratory plasma under conditions similar to those obtained in equatorial F‐region plasma, are presented. Essential characteristics of the bottom side of the night time equatorial F‐region plasma, viz., density gradient antiparallel to gravity and perpendicular to the magnetic field, and magnetized electrons and ions are simulated in a toroidal laboratory plasma, where curved magnetic field produces effective gravity. Low frequency (ω < Ωi,kpi « 1) waves travelling in E × B direction are observed. The one dimensional k‐spectrum (S(k) ∝ kn) of density fluctuations exhibits two marked slopes with indices n = −2.3 ± 0.3 and −4.4 ± 0.2. Results are similar to the in‐situ measurements in F‐region and support theoretical predictions and numerical simulations based on Rayleigh‐Taylor and universal drift instabilities.