Персона: Мельников, Александр Владимирович
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Институт лазерных и плазменных технологий
Стратегическая цель Института ЛаПлаз – стать ведущей научной школой и ядром развития инноваций по лазерным, плазменным, радиационным и ускорительным технологиям, с уникальными образовательными программами, востребованными на российском и мировом рынке образовательных услуг.
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Мельников
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Александр Владимирович
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- ПубликацияОткрытый доступActive control of Alfven eigenmodes in magnetically confined toroidal plasmas(2019) Garcia-Munoz, M.; Sharapov, S. E.; VanZeeland, M. A.; Ascasibar, E.; Melnikov, A. V.; Мельников, Александр ВладимировичAlfven waves are electromagnetic perturbations inherent to magnetized plasmas that can be driven unstable by a free energy associated with gradients in the energetic particles' distribution function. The energetic particles with velocities comparable to the Alfven velocity may excite Alfven instabilities via resonant wave-particle energy and momentum exchange. Burning plasmas with large population of fusion born super-Alfvenic alpha particles in magnetically confined fusion devices are prone to excite weakly-damped Alfven eigenmodes (AEs) that, if allowed to grow unabated, can cause a degradation of fusion performance and loss of energetic ions through a secular radial transport. In order to control the fast-ion distribution and associated Alfvenic activity, the fusion community is currently searching for external actuators that can control AEs and energetic ions in the harsh environment of a fusion reactor. Most promising control techniques are based on (i) variable fast-ion sources to modify gradients in the energetic particles' distribution, (ii) localized electron cyclotron resonance heating to affect the fast-ion slowing-down distribution, (iii) localized electron cyclotron current drive to modify the equilibrium magnetic helicity and thus the AE existence criteria and damping mechanisms, and (iv) externally applied 3D perturbative fields to manipulate the fast-ion distribution and thus the wave drive. Advanced simulations help to identify the key physics mechanisms underlying the observed AE mitigation and suppression and thus to develop robust control techniques towards future burning plasmas.
- ПубликацияОткрытый доступExperimental observation of the geodesic acoustic frequency limit for the NBI-driven Alfven eigenmodes in TJ-II(2021) Eliseev, L. G.; Ascasibar, E.; Cappa, A.; Drabinskiy, M.; Melnikov, A. V.; Мельников, Александр Владимирович© 2021 Author(s).We study Alfvén eigenmodes (AEs) in the TJ-II heliac in hydrogen plasmas heated by hydrogen co-field neutral beam injector. Taking advantage of the unique TJ-II flexibility in a varying plasma current, we have observed strong variation of the AE frequency from fAE ∼30 to ∼220 kHz for selected modes. An advanced heavy-ion beam probe diagnostic determines the spatial location and internal amplitudes of the modes. The modes satisfy a local AE dispersion relation including the geodesic acoustic frequency that represents the lowest frequency of the mode. Linear MHD modeling with STELLGAP and FAR3D codes shows that the calculated temporal evolution of the mode frequency reproduces the observed maxima and minima at the same time intervals with a similar frequency range, and the radial profile peaks near the outer edge of the observed one.
- ПубликацияОткрытый доступEvolution of heavy ion beam probing from the origins to study of symmetric structures in fusion plasmas(2021) Melnikov, A.; Мельников, Александр Владимирович© 2021 by the authorLicensee MDPI, Basel, Switzerland.The overview discusses development of the unique fusion plasma diagnostics—Heavy Ion Beam Probing (HIBP) in application to toroidal magnetic plasma devices. The basis of the HIBP measurements of the plasma electric potential and processing of experimental data are considered. Diagnostic systems for probing plasma in tokamaks TM-4, TJ-1, TUMAN-3M and T-10, stellarators WEGA, TJ-II and Uragan-2M are presented. Promising results of the HIBP projects for various existing modern machines, such as TCV, TCABR, MAST, COMPASS, GLOBUS-M2, T-15 MD and W7-X and the international fusion tokamak reactor ITER are given. Results from two machines with similar size and plasma parameters, but with different types of the magnetic con-figuration: axisymmetric tokamak T-10 and helically symmetric stellarator TJ-II are compared. The results of studies of stationary potential profiles and oscillations in the form of quasimonochromatic and broadband fluctuations, turbulent particle flux, fluctuations of density and poloidal magnetic field are presented. The properties of symmetric structures—zonal flows and geodesic acoustic modes of plasma oscillations as well as Alfvén Eigenmodes excited by fast particles from neutral beam injection heating are described. General trends in the behavior of electric potential and turbulence in magnetized fusion plasmas are revealed.
- ПубликацияОткрытый доступApplication of high frequency biasing and its effect in STOR-M tokamak(2020) Basu, D.; Nakajima, M.; Melnikov, A. V.; Martinell, J. J.; Мельников, Александр ВладимировичA pulsed oscillating power amplifier has been developed to apply high frequency biasing voltage to an electrode at the edge of the STOR-M tokamak plasma. The power amplifier can deliver a peak-to-peak oscillating voltage +/- 60 V and current 30 A within the frequency range 1 kHz-50 kHz. The electrode is located in the equatorial plane at radius rho = 0.88. The frequency of the applied voltage has been varied between discharges. It is observed that the plasma density and soft x-ray intensity from the plasma core region usually increase at lower frequency regime 1 kHz-5 kHz as well as relatively higher frequency regime 20 kHz-25 kHz but seldom increase in between them. Increment of tau\!(E)has been observed 40% and 20% for the frequency regimes of 1 kHz-5 kHz and 20 kHz-25 kHz, respectively, and tau\!(p)increment is 25% for both frequency regimes. Transport simulation has been carried out using the ASTRA simulation code for STOR-M tokamak parameters to understand the physical process behind experimental observations at the higher frequency branch. The model is based on geodesic acoustic mode(GAM) excitement at resonance frequency associated with Ware-pinch due to the oscillating electric field produced by biasing voltage, which can suppress anomalous transport. Simulation results reproduce the experimental trends quite well in terms of the density, particle confinement, as well as energy confinement time evolution. All the results indicate that high frequency biasing is capable of improving confinement efficiently.
- ПубликацияТолько метаданныеBispectral analysis of broadband turbulence and geodesic acoustic modes in the T-10 tokamak(2021) Riggs, G. A.; Nogami, S. H.; Koepke, M. E.; Melnikov, A. V.; Мельников, Александр ВладимировичLocal fluctuations of electrostatic potential, poloidal electric field, magnetic potential and electron density are simultaneously measured in the T-10 tokamak by a heavy ion beam probe (HIBP) having a five-slit energy analyser, which allows an estimate of the turbulent particle flux and E x B rotation velocity in the off-minor-axis gradient zone of the toroidal plasma column. The high spatial and temporal resolution of the modern multichannel HIBP makes it an effective tool to study plasma oscillations. Motivated by previous work that has documented time-resolved interactions between measured plasma parameters using correlation analysis (coherence of E-pol and density n(e), and cross-phase), a new result from bicorrelation analysis (bicoherence of magnetic potential A(zeta) and density n(e), and biphase) is reported for documenting the evidence of wave-wave coupling and energy transfer associated with the interaction between geodesic acoustic modes (GAM) and broadband, quasi-coherent modes.
- ПубликацияТолько метаданныеTopology of 2D turbulent structures based on intermittence in the TJ-II stellarator(2021) van Milligen, B. P.; Melnikov, A. V.; Carreras, B. A.; Garcia, L.; Мельников, Александр ВладимировичThis work estimates the degree of turbulent intermittence of the plasma potential measured by a heavy ion beam probe in the core plasma region of the TJ-II stellarator. It is shown that the intermittence varies in a significant way with the plasma state (ion or electron root). In addition, radial minima of the intermittence are found to be associated with the location of topological structures of the flow associated with some important low-order rational surfaces. The local pressure gradient was also estimated, and a clear correlation was found between the steepening of the pressure gradient and the deepening of the minima of the intermittence, suggesting that the minima are associated with pressure gradient driven modes. By estimating the rotation velocity of the plasma from the measured plasma potential, it was possible to make a rough reconstruction of the two-dimensional radial-poloidal map of intermittence, thus clarifying the topological structure of the intermittence. The experimental results were put into context by comparing with simulations performed using a resistive magneto-hydrodynamic turbulence model.
- ПубликацияТолько метаданныеTransport model of plasma heating at the second harmonic of the electron cyclotron frequency(2021) Dnestrovskij, Y. N.; Danilov, A. V.; Dnestrovskij, A. Y.; Lysenko, S. E.; Melnikov, A. V.; Мельников, Александр ВладимировичThe optical thickness of the plasma is often insufficient to fully absorb the microwaves during heating at the second harmonic of the electron cyclotron frequency. An analysis of the experiments to the T-10 tokamak allows us to find the criteria for the full absorption, and to construct a canonical profile transport model for the full and partial absorptions of microwaves. The conditions to the equivalence of discharges in different tokamaks, and in a pair of tokamaks with the optimized W7-X stellarator are formulated. For equivalent discharges, calculations to the T-15MD tokamak under construction with the obtained model coincide with measurements of electron and ion temperatures in the W7-X over a wide range of plasma densities. The validated model is used to analyze future shots of T-15MD.
- ПубликацияТолько метаданныеModeling of frequency-sweeping Alfven modes in the TJ-II stellarator(2024) Ghiozzi, A.; Mantsinen, M. J.; Pastells, P.; Spong, D. A.; Melnikov, A. V.; Мельников, Александр Владимирович
- ПубликацияТолько метаданныеMagnetic Component of Quasi-coherent Mode of Plasma Fluctuations in Ohmic Plasma of the T-10 Tokamak(2024) Sergeev, N. S.; Melnikov, A. V.; Eliseev, L. G.; Сергеев, Никита Сергеевич; Мельников, Александр Владимирович
- ПубликацияОткрытый доступConceptual study of an ICRH traveling wave antenna (TWA) for T-15MD at 60 MHz(2020) Melnikov, A. V.; Messiaen, A. M.; Ragona, R.; Sushkov, A. V.; Ongena, J.; Мельников, Александр Владимирович© 2020 American Institute of Physics Inc.. All rights reserved.This paper proposes a Traveling Wave Antenna for ICRH heating of T-15MD located below the equatorial plane of the tokamak for operation at 60MHz. Resonant ring feeding allows the recirculation of the RF power that is not radiated to the plasma and the termination of the TWA section in its iterative impedance. The paper describes the antenna design, the feeding ring tuning algorithm and expected performances of this antenna concept. The chosen geometry of the TWA sections is compatible with that of a future reactor and therefore this ICRH antenna system for T-15MD also represents a test bed for DEMO.