Stimulated electromagnetic emissions and anomalous HF wave absorption near electron gyroharmonics

Abstract

Simultaneous observations are presented of stimulated electromagnetic emission (SEE) spectra and the anomalous absorption of a diagnostic HF wave, caused by powerful radio waves generated by the Tromsø heating facility. The pump frequency was varied in small steps around the third, fourth, and fifth harmonic of the electron gyrofrequency. Systematic variations with pump frequency were observed in the anomalous absorption data and the entirety of SEE properties. The anomalous absorption exhibits a pronounced minimum at a certain pump frequency near (or at) the gyroharmonic in question. Of the SEE properties the strength and discreteness of the downshifted maximum and the width of the downshifted continuum minimize together with the anomalous absorption. Other SEE properties (namely the broad upshifted maximum, the downshifted peak, and the broad symmetrical structure) exist only in well‐defined narrow pump frequency ranges near the absorption minimum. Significant quantitative and qualitative differences are found between the SEE properties around the third gyroharmonic on the one hand, and the fourth and fifth gyroharmonics on the other hand.