STIMULATED ELECTROMAGNETIC EMISSIONS AND ANOMALOUS HF WAVE ABSORPTIONNEAR ELECTRON GYROHARMONICS

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 Tromphi heating facility. The pump frequency was varied in small steps around the thi rd, fourth, and fifth harmonic of the electron gyrofrequency. Systemat ic variations with pump frequency were observed in the anomalous absor ption data and the entirety of SEE properties. The anomalous absorptio n exhibits a pronounced minimum at a certain pump frequency near (or a t) the gyroharmonic in question. Of the SEE properties the strength an d discreteness of the downshifted maximum and the width of the downshi fted continuum minimize together with the anomalous absorption. Other SEE properties (namely the broad upshifted maximum, the downshifted pe ak, and the broad symmetrical structure) exist only in well-defined na rrow pump frequency ranges near the absorption minimum. Significant qu antitative and qualitative differences are found between the SEE prope rties around the third gyroharmonic on the one hand, and the fourth an d fifth gyroharmonics on the other hand.