On ion gyro-harmonic structuring in the stimulated electromagnetic emission spectrum during second electron gyro-harmonic heating

Abstract

Abstract. Recent observations show that, during ionospheric heating experiments at frequencies near the second electron gyro-harmonic, discrete spectral lines separated by harmonics of the ion-gyro frequency appear in the stimulated electromagnetic emission (SEE) spectrum within 1 kHz of the pump frequency. In addition to the ion gyro-harmonic structures, on occasion, a broadband downshifted emission is observed simultaneously with these spectral lines. Parametric decay of the pump field into upper hybrid/electron Bernstein (UH/EB) and low-frequency ion Bernstein (IB) and oblique ion acoustic (IA) modes is considered responsible for generation of these spectral features. Guided by predictions of an analytical model, a two-dimensional particle-in-cell (PIC) computational model is employed to study the nonlinear processes during such heating experiments. The critical parameters that affect the spectrum, such as whether discrete gyroharmonic on broadband structures is observed, include angle of the pump field relative to the background magnetic field, pump field strength, and proximity of the pump frequency to the gyro-harmonic. Significant electron heating along the magnetic field is observed in the parameter regimes considered.

First observations of minority ion (H+) structuring in stimulated radiation during second electron gyroharmonic heating experiments

“…The dotted grid lines are at f cO harmonics, and the dashed grid lines are at f cH . The broader SEE line is due to the oblique ion acoustic decay instability with embedded oxygen gyroharmonic structuring [Samimi et al, 2012Mahmoudian et al, 2013]. The narrow emission line at n = 1 is about 2f cO below f cH and has bandwidth less than f cO .…”

“…Figure 3 shows the beginning of relatively rapid reduction in absorption during the heating experiment which would allow development of the IA line. The IA lines are only observed during periods of negligible absorption [Samimi et al, 2012Mahmoudian et al, 2013]. It is postulated that this disturbed event is associated with proton precipitation that produced significant quantities of H + for short periods [Ebihara et al, 2010].…”

“…uh = 2 e , where ! uh is the upper hybrid frequency and [Samimi et al, 2012Mahmoudian et al, 2013]. Equation (2) has been solved numerically with different input parameters of electron and ion temperature ratio, strength of the pump field calibrated with electron oscillating velocity v osc = eE 0 /m e !…”

“…Figure 4a shows dispersion relation and growth rate against the wave number, and Figure 4b shows the growth rate against the real frequency. Samimi et al, 2012Samimi et al, , 2013 and due to energy degradation T H /T i = 1; however, the importance of variation of this parameter will be discussed shortly. The electron density is n e = 3 10 5 cm -3 , and the temperature T e = 2500K.…”

Stimulated Brillouin scattering during electron gyro-harmonic heating at EISCAT

“…During the past few years, SEE observations at HAARP have revealed a plethora of narrowband SEE lines associated with SBS and stimulated ion Bernstein scatter (SIBS) (e.g. Norin et al, 2009;Bernhardt et al, 2009Bernhardt et al, , 2010Samimi et al, 2012Samimi et al, , 2013Samimi et al, , 2014. further investigated SBS and SIBS and their interrelationship in detail over a range of aspect beam angles and frequency stepping near electron gyro-harmonics.…”