Papers by Alexander Shalashov
Simple Approach to Electromagnetic Scattering by Small Radially Inhomogeneous Spheres
IEEE Transactions on Antennas and Propagation, 2016
We consider the linear mechanism of electron-cyclotron current drive (CD) in the case of quasitra... more We consider the linear mechanism of electron-cyclotron current drive (CD) in the case of quasitransverse launch of microwave power from the low-field side of a toroidal system for plasma confinement. In this specific scenario, the electromagnetic-field energy is absorbed mainly by lowenergy thermal electrons under conditions of electron-cyclotron resonance (ECR) with allowance for both the Doppler shift and the relativistic dependence of the electron mass. Under these conditions, degradation of the CD efficiency or even current reversal with respect to the direction of microwave-beam launch can occur. The kinetic equation is analyzed by the method of "adjoint" equation for the current, which allows for the accurate treatment of electron-electron collisions for an arbitrary effective charge of the ion component.
Acceleration of electrons during the magnetic compression of coronal plasmas
Attenuation of Bragg backscattering of electromagnetic waves from density fluctuations near the region of polarization degeneracy in magnetoactive plasma
Plasma Physics Reports, 2016
Formation of a Multi-Charged Plasma in the Directed Gas Flow
Radiophysics and Quantum Electronics, 2016
Radiophysics and Quantum Electronics, 2012
We consider the linear coupling of waves in the electron-cyclotron frequency range in a nonone-di... more We consider the linear coupling of waves in the electron-cyclotron frequency range in a nonone-dimensional inhomogeneous magnetized plasma in the vicinity of the plasma cutoff surface with allowance for their collisional dissipation. Model wave equations describing the normal wave interaction in the considered case are formulated and solved analytically. Effects of the absorption anisotropy typical of magnetized plasma on the linear mode coupling in two-dimensional inhomogeneous geometry are analyzed. *
Plasma Physics and Controlled Fusion, 2014
The theory of the linear coupling between the ordinary and extraordinary electron cyclotron waves... more The theory of the linear coupling between the ordinary and extraordinary electron cyclotron waves in the vicinity of the plasma cut-off has been generalized for configurations with harmonic perturbations of plasma density, which is relevant, in particular, to the magnetic flux fluctuations in a toroidal fusion experiment. It is shown that for a large aspect ratio, tokamak fluctuations result in the amplitude and phase distortion of the quasi-optical beam on its way towards the coupling region located near the cut-off layer, but have no essential influence on the efficiency of the mode interaction inside the coupling region. However, this may not be valid in a spherical tokamak, where the perturbations may be significant inside the coupling region. We find that density fluctuations cannot be fully responsible for a low efficiency of the OXB heating of the overdense plasma observed in the present-day experiments.
Plasma cyclotron maser with a magneto-compressional pumping
The capabilities of modern vacuum electronic devices with respect to accumulation of energy in an... more The capabilities of modern vacuum electronic devices with respect to accumulation of energy in an “active substance” and control of the duration of resultant electromagnetic radiation are constrained by the interaction time of an electron beam with the radiation limited by the beam transit through a resonator. Using non-equilibrium plasma as an active substance opens new possibilities for long-lasting accumulation of energy in a resonator volume with subsequent release of this energy in the form of a short pulse of electromagnetic radiation. Energy may be effectively pumped by a magnetic compression in time resulting in formation of non-equilibrium energetic tails in the electron distribution function. The energy of fast electrons may be released as coherent maser electromagnetic radiation due to development of electron cyclotron (EC) instabilities caused by the anisotropy of the electron distribution function. The radiation frequency is determined by the magnetic field strength at ...
Chirp Ionosonde-Radiodirection Finder as a New Tool for Studying the Ionosphere and Radio-Wave Propagation
Radiophysics and Quantum Electronics
ABSTRACT Hardware of a chirp ionosonde–radiodirection finder, which, along with the conventional ... more ABSTRACT Hardware of a chirp ionosonde–radiodirection finder, which, along with the conventional parameters, measures angular frequency characteristics on oblique ionospheric sounding paths, is briefly described. The results of the experimental studies of propagation of radio waves on paths of different length and orientation in the natural and artificially disturbed ionosphere are presented. Capabilities of the ionosonde–radiodirection finder for over-the-horizon HF radio detection and ranging of the Earth’s ionosphere on a global scale are shown.
Radiophysics and Quantum Electronics, 2013
In this work, we discuss experimental evidence for the existence of an effective mechanism of ene... more In this work, we discuss experimental evidence for the existence of an effective mechanism of energetic-electron losses at the initial stage of the discharge during electron cyclotron resonance (of the ECR discharge) when the electron scattering to the loss cone is caused by the development of the electron cyclotron instabilities of a strongly nonequilibrium plasma. The spectral composition of the transient pulses of electromagnetic radiation is studied in a wide frequency range at the initial stage of the ECR discharge, when the hot-particle density exceeds that of cold particles. The observed electromagnetic-radiation bursts and synchronous energetic-electron precipitation from the trap can be related to the development of a cyclotron instability of the fast extraordinary wave in the rarefied plasma. *
Radiophysics and Quantum Electronics, 2006
Linear conversion of the ordinary wave to the extraordinary wave and then to the Bernstein wave (... more Linear conversion of the ordinary wave to the extraordinary wave and then to the Bernstein wave (O-X-B conversion) in a tokamak plasma is considered in the generalized geometric-optical approximation taking into account the relativistic effects in a dielectric permitivity tensor. Using the T-10 tokamak as an example, it is shown that even for a relatively low plasma temperature (about 1 keV at the plasma-column center) relativistic effects exert a notable influence on the cyclotron absorption of Bernstein waves. Power deposition profiles for O-X-B plasma heating are determined. The emission of spontaneously excited Bernstein waves resulting from the B-X-O conversion are considered. . 617 plasma density. As the region with a certain plasma density is reached, the X wave turns back (is reflected) and propagates in the reverse direction (of decreasing plasma density) up to the upper-hybrid resonance region where ω = ω uh ≈ ω 2 pe + ω 2 ce . In this region, secondary conversion of the X wave to an electron Bernstein wave (B mode) occurs. Upon conversion to the B wave, the radiation freely propagates toward the magnetic-field increase, including the supercritical plasma region (ω pe > ω), and reaches the EC resonance region where the radiation absorption and plasma heating take place. The optimal angle of electromagneticradiation input for actual setups can be searched with the use of codes for geometric-optical calculation of the ray trajectories modified in a certain way for taking into account the linear wave conversion effect. This scheme of plasma heating was implemented experimentally, in particular, using such large setups as W7-AS , MAST [2,, and, recently, TCV .
Nuclear Fusion, 2015
This paper summarizes the results of experiments on electron cyclotron resonance heating (ECRH) o... more This paper summarizes the results of experiments on electron cyclotron resonance heating (ECRH) of plasma obtained at the axially symmetric magnetic mirror device gas dynamic trap (GDT) (Budker Institute, Novosibirsk). The main achievement is the demonstration of plasma discharges with extremely high temperatures of bulk electrons. According to the Thomson scattering measurements, the on-axis electron temperature averaged over several sequential shots is 660±50 eV with peak values exceeding 900 eV in a few shots. This corresponds to an at least threefold increase as compared to previous experiments both at the GDT and at other comparable machines, thus demonstrating the maximum quasi-stationary (∼0.6 ms) electron temperature achieved in open traps. The breakthrough is made possible with the successful implementation of a sophisticated ECRH scheme in addition to standard heating by neutral beams (NBs). Another important result is the demonstration of the significantly increased lifetime of NB-driven fast particles with the application of ECRH, leading to a 30% higher plasma energy content at the end of the discharge. All available data including the previously demonstrated possibility of plasma confinement with β as high as 60%, allows us to consider fusion applications of axially symmetric magnetic mirror machines on a realistic basis.
Coupling of electron cyclotron waves in toroidal plasmas with fluctuations
On method of problem solution of bound electromagnetic wave propagation in plane-laminar magnetoactive plasma
Mode-impedance for modeling of electromagnetic wave propagation in plasma
About electromagnetic wave transformation near surface of critical concentration in three-dimensional inhomogeneous magneto-active plasma with magnetic field shear
Linear conversion of electromagnetic waves in cylindrical two-dimensionally inhomogeneous magnetoactive plasma
We demonstrate plasma discharges with extremely high temperature of bulk electrons at the large a... more We demonstrate plasma discharges with extremely high temperature of bulk electrons at the large axially symmetric magnetic mirror device GDT (Budker Institute, Novosibirsk). According to Thomson scattering measurements, the on-axis electron temperature averaged over several sequential shots is 660 ± 50 eV with peak values exceeding 900 eV in few shots. This corresponds to at least threefold increase as compared to previous experiments both at the GDT and at other comparable machines, thus demonstrating the maximum quasi-stationary (∼ 1 ms) electron temperature achieved in open traps. The breakthrough is made possible with application of sophisticated electron cyclotron resonance heating in addition to standard heating by neutral beams. The reported increase of the electron temperature along with previous experiments, which demonstrated highdensity plasma confinement with β ≈ 60%, provide a firm basis for extrapolating to fusion relevant applications of open magnetic systems.
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Papers by Alexander Shalashov