Langmuir wave turbulence generated by electromagnetic waves in the laboratory and the ionosphere

Summary form only given, as follows. We will present some recent results of our laboratory experiments at MIT, using a large plasma device known as the versatile toroidal facility (VTF). These experiments are aimed at cross-checking our ionospheric plasma heating experiments at Arecibo, Puerto Rico using an HF heating facility (heater). The plasma phenomenon under investigation is the spectral characteristic of Langmuir wave turbulence produced by ordinary (o-mode) electromagnetic pump waves. The Langmuir waves excited by o-mode heater waves at Arecibo have both a frequency-upshifted spectrum and a frequency-downshifted (viz., cascading) spectrum. While the cascading spectrum can be well explained in terms of the parametric decay instability (PDI), we have interpreted the frequency-upshifted Langmuir waves to be anti-Stokes Langmuir waves produced by a nonlinear scattering process as follows. Lower hybrid waves created presumably by lightning-induced whistler waves can scatter nonlinearly the PDI-excited mother Langmuir waves, yielding obliquely propagating Langmuir waves with frequencies as the summation of the mother Langmuir wave frequencies and the lower hybrid wave frequencies. This suggested process has been confirmed in our laboratory experiments, that can reproduce the characteristic spectra of Langmuir wave turbulence observed in our Arecibo experiments.