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.

Laboratory studies o fkinetic instabilities under double plasma resonance condition in a mirror-confined nonequilibriumplasma mirror configuration of magnetic-field lines. The magnetic field is produced by pulse coils (the current pulse duration is 7 ms), which ensure a magnetic field of 4.3 T in the trap mirrors, and a mirror ratio of 5. The working gas used in the experiments is nitrogen. The background pressure of the neutral gas is 10 ” 6 Torr, and the operating pressure at the moment of the discharge can increase up to ICf 3 Torr. F ig u r e 1. Layout of the experimental setup: gyrotron (/), dielectric lens (2), discharge chamber (J), magnetic mirror ( 4 ), pulse valve (5), receiving volume with the working gas (6), p-i-n-diode on a movable support (7), Langmuir probe (5), and antennas for detection of microwave radiation (9 and 10). The arrow shows the direction of evacuation. In this work, the main attention is given to the studies of electromagnetic plasma activity, specifically, measurements of the spectral composition of plasma emission bursts. Additionally, a set of traditional methods [9, 1 1 ] is used to measure plasma parameters and characteristics of the energetic electrons precipitating from the trap along the magnetic field. A set of silicon p-i-n diodes capable of detecting particles with energies from 10 to 180 keV and a single plane electric probe operating in the ion saturation current regime are used as detectors of electrons. The own electromagnetic radiation of the plasma is detected both along and across the magnetic field of the trap using receiving antennas located out of the vacuum volume. To detect plasma radiation, we used a horn antenna with a uniform passband in the range from 2 to 20 GHz. The signal from the antenna is sent to the wide-band Tektronix MS072004C oscilloscope with the 20 GHz passband of the analog channel and a maximum time resolution of 10 ps. Alongside the horn antenna, a low-pass filter with a boundary frequency of 18.5 GHz is used to protect the channels of the oscilloscope against the high-power radiation of the gyrotron. 3. Experimental results The use of high-power millimeter-wave radiation of the gyrotrons for heating of electrons under the cyclotron resonance conditions allows one to produce a nonequilibrium plasma with unique parameters. The plasma at the stage of a well-developed discharge is characterized by the presence of a dense cold component (the density Nc ~ 10 13 cm"3, temperature Tc~ 300 eV) with isotropic velocity distribution and a less dense hot electron fraction (the density Nh ~ 10w-40 " cm”3, the average particle energy Th ~ 100 keV) with anisotropic distribution function [11, 14]. The cold background plasma determines the dispersive properties of waves in the medium, whereas the hot electron component with a nonequilibrium velocity distribution determines the instability and generation of electromagnetic radiation under conditions where the loss-cone is empty. The used equipment allows one to study the microwave plasma radiation at frequencies of 2 to 20 GHz with time resolution exceeding 1 ns. Fig. 2 shows the oscillogram of the electric field component of the plasma electromagnetic radiation. Fig. 3 shows the dynamic spectrum of plasma radiation, which was obtained by using the windowed Fourier transform, and the corresponding oscillogram of the electron detector signal immediately after the microwave radiation of the gyrotron is turned off. Here and in what follows, the shades of gray in the spectrogram indicate the power spectral density on a logarithmic scale. Analysis of the experimental data allows one to determine characteristic parameters of the pulse-periodic instability regime. Radiation bursts occur at a frequency near 2fce0, where f a 0 = <»«</( 2л) is the electron gyrofrequency at the center of the magnetic trap, duration of flares and synchronous bursts of the current of the electrons precipitating from the trap is equal to about 50 ns, and the period of their repetition is about 200 ns. It is important to note here that the upper-hybrid radiation is observed at the moment, when the frequency / uh of the upper hybrid resonance becomes equal to the second harmonic of the electron gyrofrequency 2fCf0 (see Fig. 3). This is an experimental proof of the double plasma resonance effect. Series of quasiperiodic bursts can consist of up to a hundred pulses. An example of such a series is shown in Fig. 4 and, with a better time resolution, in Fig. 5. A few of such periodical groups can follow each other at an interval of approximately 50 /vs. 65