REMOTE DIAGNOSTICS OF EFFECTS INDUCED BY HIGH-LATITUDE HEATING FACILITIES

The results of long-term studies of the effects of the high-latitude ionosphere modification by powerful high-frequency (HF) radio waves generated by the EISCAT/Heating facility based on remote diagnostic methods are presented. The brief description of remote diagnostic instruments and methods is given. The excitation conditions and characteristics of small-scale artificial field-aligned irregularities induced by the O- and X-mode HF pumping are considered using the bi-static scatter method. The results of the spectral analysis of HF heater signals under various radiation modes are provided. It is shown that the X-mode HF pumping induces narrowband artificial radio emission of the ionosphere recorded at a distance of more than 1000 km from the heater.

Mesosphere Ozone and the Lower Ionosphere under Plasma Disturbance by Powerful High-Frequency Radio Emission

We present the results of experiments on the Earth’s lower ionosphere at mesospheric heights by creating artificial periodic irregularities (APIs) of the ionospheric plasma and simultaneous measurement of the atmospheric emission spectrum in the ozone line by ground-based microwave radiometry when the ionosphere was disturbed by powerful high-frequency radio emission from the midlatitude SURA heating facility (56.15° N; 46.11° E). The diagnostics of the ionosphere was carried out on the basis of measuring amplitudes and phases of signals scattered by periodic irregularities in the altitude range of 50–130 km. For each heating session lasting 30 min, two ozone spectra were measured. These spectra were compared with the measured spectra the periods when heating was turned off. During the heating session of the ionosphere, a decrease in the intensity of the microwave radiation of the atmosphere in the ozone line was observed. The lower ionosphere was characterized by intense dynamics. Rapid variations in the amplitude of the scattered signal and the relaxation time of artificial periodic irregularities were observed. The velocity of a regular vertical movement in the D-region of the ionosphere constantly varied direction with average minute values up to 4–5 m/s. We assume the decrease in the ozone emission spectrum at the altitude of 60 km can be explained by an increase in the coefficient of electron attachment to oxygen molecules during heating sessions. The lower boundary of the region enriched with atomic oxygen was estimated from the height profile of the API relaxation time.

Physical Optics

Physical optics (PO) is one of the fundamental and powerful high-frequency theories for electromagnetic scattering and radiation. The total field of a source (antenna) which radiates in the presence of a perfectly conducting surface may be expressed as a superposition of the incident and the scattered fields. The current fields which exist everywhere are chosen in PO to denote the electric and magnetic fields of the source, i.e., they exist as if the scatterer was “absent”; this is unlike the geometrical optics (GO) incident field, which exists in the presence of the surface of the scatterer. The scattered fields in this case can be expressed in terms of the radiation integrals over the actual currents induced on the surface of the scatterer. These currents also radiate the scattered fields in the absence of the scatterer. This chapter shows the fundamental PO formulation and calculated results, and some topics which improve the conventional PO to the extended PO such as “physical theory of diffraction (PTD)” and “PO with transition current (PTD-TC)”.

GENERATOR OF POWERFUL HIGH-FREQUENCY PACKAGE CURRENT PULSES FOR POWER SUPPLY OF ULTRASONIC ELECTROMAGNETIC-ACOUSTIC TRANSDUCERS

It is possible to increase the sensitivity of electromagnetic-acoustic transducers by three main methods: increasing the induction of a polarizing magnetic field; increase in strength of high-frequency current in the inductor of the converter; using modern methods of processing information packet pulses excited and received from the product. The increase in magnetic field induction of the converter is limited by the capabilities of modern powerful permanent magnets. In addition, there are significant difficulties in monitoring ferromagnetic control samples, due to the large pressing force between the sample and the transducer and sticking of scale to the transducer. Usage of modern processing methods significantly complicates and increases the cost of electromagnetic-acoustic testing devices. Of the selected sensitivityincreasingmethods, the most acceptable way is to increase the power of high-frequency current generators under the condition of excitation of packet pulses. Power supply process of the converter is carried out in two stages. Meander type powerful high-frequency current pulses are excited, which ensures operation of the output transistors in key mode. Isolation of a powerful sinusoidal high-frequency packet current pulse is carried out directly on the electromagnetic - acoustic transducer, the elements of which are included in the resonant circuit with low quality factor. Based on the transistors switched in the push-pull circuit in the key mode, a small-sized generator design has been created that excites a peak current of up to 800 A in the electromagnetic-acoustic transducer and a voltage of up to 3 kV in the transducer in the frequency range 0.3 ... 8 MHz. It was experimentally determined that the new design of the probe pulse generator made it possible to increase the amplitude of pulses reflected from a flat-bottom reflector with a diameter of 2 mm with respect to the interference amplitude by more than 2 times.

Investigations of Atmospheric Waves in the Earth Lower Ionosphere by Means of the Method of the Creation of the Artificial Periodic Irregularities of the Ionospheric Plasma

We present results of the studies of internal gravity waves based on altitude-time dependences of the temperature and the density of the neutral component and the velocity of the vertical plasma motion at altitudes of the lower ionosphere (60–130 km). The vertical plasma velocity, which in the specified altitude range is equal to the velocity of the neutral component, the temperature, and the density of the neutral atmosphere are determined by the method of the resonant scattering of radio waves by artificial periodic irregularities (APIs) of the ionosphere plasma. We have developed an API technique and now we are evolving it for studying the ionosphere and the neutral atmosphere using the Sura heating facility (56.1 N; 46.1 E), Nizhny Novgorod, Russia. An advantage of the API technique is the opportunity to determine the parameters of the undisturbed natural environment under a disturbance of the ionosphere by a field of powerful high frequency radio waves. Analysis of altitude-time variations of the neutral temperature, the density, and the vertical plasma velocity allows one to estimate periods of atmospheric waves propagation. Wavelike variations with a period from 5 min to 3 h and more are clearly determined.

Small High Frequency Powerful Vibrator and its Application to Underwater Sound Generator

The author has developed a small and powerful high frequency cam-type vibrator using roller thrust bearings with uneven races. The diameter of the vibrator is nearly the same as the outer diameter of the thrust bearing, and it is very small compared with other vibrators. This vibrator can be installed at the bottom end of a drill string as a high frequency vibro-hammering gear. Although the amplitude of the axial displacement is fixed, combination of two vibrators of this type can make the amplitude variable by superimposition. This variable superimposition can also be used as an On-Off switch of the vibration. The underwater sound used for seismic survey is usually a short pulse with a duration of several to several tens of milliseconds. The vibrator described in this paper is capable of generating such short sound pulses owing to the variable superimposition. Present sound generators for seismic survey are usually big and heavy and generate sound pulses with a wide frequency spectrum, centered around 100Hz. The cam-type vibrator described in this research is much smaller and lighter than present systems, making the deployment near the seafloor easy for even at great depths, which in return leads to more detailed results in stratum surveys. The emitted sound is a pure tone whose frequency can be anywhere between 100 and 1000Hz. The author has tried to develop this type of sound generator under the support of JOGMEC (Japan Oil, Gas and Metals National Corporation). In this paper, the principle of the vibration, the design of the sound generator and the result of the experiment shall be discussed.