Physics of auroral phenomena : proceedings of the 38th annual seminar, Apatity, 2-6 march, 2015 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Издательство Кольского научного центра РАН, 2015. - 189 с. : ил., табл.

M.E. Viktorox et al. electromagnetic radiation appears (at the time moment t = 1 1 0 0 ц s), the plasma density is equal to 2 X 1 0 n cm 3. Under these conditions, the plasma frequency exceeds the electron gyrofrequency at the center of the trap (&v > coce0); therefore, the whistler waves at frequencies below co ce0 and plasma waves at the upper hybrid frequency have the largest growth rates [16]. time, рл time, /is Figure 6 . Calculation of the plasma decay after switching-off the ECR heating based on the balance equations for the densities of neutral and charged particles and the stored energy, which are averaged over the trap volume (in greater detail, see [15]): variation in the density Nc ( a ) and temperature TQ ( b ) of the background plasma electrons. The calculation is performed for the initial parameters Nc0 = 10 13 cm ' 3, 7’cO= 300 eV. Analysis shows that in the experiment discussed here, the unstable waves are mainly the plasma waves at the upper hybrid frequency, whose growth rates exceed those of other unstable modes by several orders of magnitude. Indeed, since the frequency of plasma waves is close to the second harmonic of electron gyrofrequency for the high- frequency component of the radiation, whose spectrum is shown in Fig. 4a, one can assume that at a certain stage of the plasma decay, the condition of double plasma resonance is fulfilled [17]: со * ^а ^+ со ^ +ЗкУт' * 2act ( 1 ) where к , is the component of the wave vector being transverse to the magnetic field B, and uT is the thermal e velocity of electrons. The fulfilment of condition (1) leads to an increase in the growth rates of plasma waves and, consequently, an increase in the energy density of these waves and the intensity of the observed radio emission. The latter occurs as a result of transformation of plasma waves to electromagnetic waves, e.g., as a result of scattering by thermal ions. Condition (1) will be fulfilled in those regions of the trap where the relation c o p e * S c o ce ( 2 ) is valid for the plasma frequency and the gyrofrequency. When condition (1) is fulfilled, the growth rate of the plasma wave is equal, in order of magnitude, to [2] Г * ( 0 . 1 + 1 ) ^ - c o ce. (3) N c The growth rate is maximum for the waves propagating across the magnetic field. The wave vector of unstable plasma waves is determined by the characteristic velocity of nonthermal resonance electrons uh and is of the order of k± « ю/и* • The group velocity of plasma waves is equal to 3 k±v$ 3uf. и « ------- * - » — *- (4) g со oh and the spatial amplification coefficient of plasma waves — + (5) ugr N c 3 v T' in this case is equal to approximately / / » 1 . 5 x ( 1 0 3 -H 0 4) cm-1. If one assumes that the instability band width Aa> is equal to approximately Aa> ~ O.lco [17], when the double plasma resonance is realized, then the integral gain for the plasma waves propagating tangentially to the magnetic- field isosurfaces can reach 3x(10 -HO4) at the plasma volume radius Rj. = 3.5 cm. This means that nonlinear effects can affect the dynamics of plasma waves significantly. Specifically, the pulse regime of plasma wave generation can 68