Vol 62, No 1 (2019)

We study the dynamics of the spectra of multiband sporadic magnetic pulsations in the Pc1 range (0.2–5.0 Hz) during the event of 5–6 March 2011 by using ground-based magnetic measurements at stations largely spaced from each other in latitude and longitude. The event is characterized by a long duration (about 16 h), the presence of several bands with varying frequencies, splitting of these bands into narrower subbands, significant variations in the amplitude and polarization of the signals on the ground, and their observation in a wide range of latitudes and longitudes. On the basis of a joint analysis of the Pc1 pulsation properties and the data of low-orbiting spacecraft detecting localized precipitations of energetic protons into the ionosphere, we infer the possible generation regions of these waves in the magnetosphere and conclude that they are multiple. The results of analysis allowed us to determine the mechanisms of broadening and splitting of Pc1 frequency bands even in the absence of direct wave observations in the magnetosphere. We also propose an explanation of the atypical (for ground-based detection) character of two-band Pc1 spectra when the signal at frequencies above the helium ion gyrofrequency has a higher amplitude than at lower frequencies. We also explain the inhomogeneous frequency profile of polarization in different frequency bands. Possible variations in the magnetospheric plasma parameters that resulted in the observed dynamics of amplitude and polarization spectra of Pc1 pulsations are revealed by using calculations of the wave cyclotron amplification by energetic protons in the magnetosphere.

We present the results of experimental studies of the oscillation regimes of the pulse signals, which are analogs of the temporal solitons, in a distributed active ring resonator with a multicavity klystron amplifier and a spin-wave transmission line. The soliton-like pulses are formed under conditions of three-wave parametric decay of a surface magnetostatic spin wave when the klystron amplifier operates in a small-signal regime. Parametric turbulence is shown to cause the chaotic nature of generated patterns, which is confirmed by the performed estimations of the senior Lyapunov exponent from experimental time series. In addition, the possibility of controlling the phase coherence, the autocorrelation time, and the noise-to-signal ratio of the generated chaotic soliton-like pulses by varying the beam current and the acceleration voltage of the klystron amplifier is demonstrated.

We study the excitation of an electromagnetic field in a compact nerve fiber by a system of given filamentary electric currents, which are aligned with the fiber. In the case of a fiber consisting of several myelinated axons, equations for the scattering coefficients of the electromagnetic waves excited by such currents are obtained. On the basis of the solution of the corresponding equations, the total field due to these sources is found in the case of their location around the fiber. An approach is proposed for determining the filamentary-current amplitudes such that it ensures the formation of the required field pattern inside the nerve fiber. Numerical results demonstrating the possibility of selective field excitation in individual axons are presented.