Experimental Study on the Parametric Generation of Very Low Frequency (VLF) Waves in a Scaled Ionospheric Environment

We investigate the parametric excitation of VLF waves due to the interaction of HF beat waves in a magnetized laboratory plasma environment with plasma parameters scaled to those found in the F-region ionosphere. The setup of the experimental system is guided by theoretical investigations which derive resonant conditions for two HF pump waves to efficiently generate VLF waves [1]. The temporal and spatially varying electrostatic amplitudes of these waves are measured using electrostatic probe techniques coupled with a 3D positioning system. The electrostatic VLF wave vectors will be estimates using analysis of the acquired data for confirmation of the underlying theory behind the parametric excitation. Further analysis is then performed to derive the electron distribution function in the region where the VLF waves are excited. Interaction of plasma electrons with waves excited with frequencies close to the Lower Hybrid (LH) frequency can lead to the appearance of non-Maxwellian energetic electron tails in the electron distribution function. We will examine experimentally the electron distribution function for cases both with and without the applied HF pump waves. The possibility of a generation of a secondary plasma discharge due to the appearance of energetic electron tails will be also discussed.