Methodology of the Murman-2018 Experiment
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odology of the Murman-2018 Experiment M. B. Barannik* Center for Physical and Technical Problems of Energy of the North—Branch of Federal Research Center, Kola Science Center, Russian Academy of Sciences, Murmansk oblast, Apatity, 184209 Russia *e-mail: [email protected] Abstract—The methodology of the Murman-2018 experiment is considered. The technique of the study is based on the distance principle of deep sounding combined with frequency and audio magnetotelluric soundings. Two mutually orthogonal grounded transmitting lines, 1.6 km and 1.9 km in length, were powered by an Energiya-4 generator, which was used as a controllable electromagnetic field source . The main focus of the paper is the description of the self-powered 29 kW Energiya-4 generator with an output voltage up to 1200 V, developed at NERC KSC RAS. The paper discusses experience of using the generator to solve of fundamental problem of studying the nature of the deep geophysical boundaries in the Archean crust of the Murmansk block in the Murman-2018 experiment. A block diagram of the Energiya-4 generator is presented and its operating principle briefly described. Keywords: controlled current source, pulse width modulation inverter, grounded transmission line, frequency sounding, distance sounding DOI: 10.3103/S0747923920050060
INTRODUCTION The Murman-2018 experiment was performed in the territory covered by Archean basement rocks of the Murmansk block, which is part of the Fennoscandinavian Shield. The main objective of the experiment was to study the nature of deep geophysical boundaries under normal section conditions, unaffected by conductivity anomalies consisting of sulfide–carbon rocks (Zhamaletdinov et al., 2019). The studies were carried out using remote and induction deep sounding principles. The experiment employed remote sensing with direct current (RS), frequency sounding in the field of a controlled source (Control Source Audio Magnetotellurics, CSAMT), and audiomagnetotelluric sounding (AMTS) in the field of natural variations. RS and CSAMT soundings were performed with axial and equatorial devices using two mutually orthogonal grounded transmission lines with lengths of 1.9 and 1.6 km. A block diagram of these transmission lines is shown in Fig. 1. During CSAMT and AMTS, measurements were performed by a VMTU-10 broadband magnetotelluric station with IMS-007 induction sensors and two M-0N mutually orthogonal symmetrical receiving electric lines, each with a length of 2 × 50 m. RS utilized the electric channels of the VMTU-10 station and a seven-channel station KVVN-7 (Kolobov et al., 2012).
ENHANCED ENERGY-4 GENERATOR AS A CURRENT SOURCE FOR RS AND CSAMT The Murman-2018 experiment used an Energiya-4 autonomous generator with a power of up to 29 kW, developed at the Center for Physical and Technical Problems of Energy of the North, Kola Science Center of the Russian Academy of Sciences (NERC KSC RAS) in 2014 (Kolobov et al., 2018a) and upgraded in 2018 for Murman-2018 (Kolobov et al., 2018). The generator is designed to for electromag
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