Научная группа: TJ-II Team
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HIGH-INTENSITY CESIUM ION BEAMS FOR HIBP DIAGNOSTICS
(2020) Krupnik, L. I.; Barcala, J.; Chmyga, O. O.; Deshko, G. M.; Melnikov, A. V.; Мельников, Александр Владимирович
The goal of the research is to expand the capabilities of the heavy ion beam probing (HIBP) diagnostic. HIBP is a unique diagnostic, capable to measure plasma potential, density and their fluctuations, as well as the poloidal magnetic field fluctuations in the core and edge plasmas. The sensitivity of the diagnostic is determined by the level of the output signal related to the instrumental noise. The level of the probing beam current should be as high as possible, especially for measurements at the periphery with low output signal due to low plasma density, and in the core, where the beam is attenuated due to the high plasma density. Optimization experiments have shown the possibility of ion beam forming in the current range from 40 to 800 mu A.
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Stability analysis of TJ-II stellarator NBI driven Alfven eigenmodes in ECRH and ECCD experiments
(2021) Cappa, A.; Varela, J.; Bruna, D. L.; Ascasibar, E.; Melnikov, A. V.; Мельников, Александр Владимирович
In this paper, we analyze the impact of electron cyclotron resonance heating and electron cyclotron current drive on the Alfvenic instabilities driven by neutral beam injection observed in the TJ-II stellarator. An MHD stability analysis of driven Alfven eigenmodes compatible with the experimental plasma parameters is carried out in order to compare with the data provided by magnetic coils, radiation monitors, and heavy ion beam probes. To this end, the vacuum magnetic configuration modified by the different levels of plasma current, the thermal plasma parameters and the fast ion pressure profiles generated by the co-injected neutral beam, are entered in the FAR3d gyro-fluid code in order to follow the linear evolution of the destabilized plasma equilibrium. Linear growth rates and radial location of the dominant predicted modes coincident in frequency with the observed fluctuations are presented. Despite the uncertainties related to the estimation of the rotational transform profile, the code predictions agree within reasonable accuracy with the experimental results.
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Topology 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 Владимирович
This 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.
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2D distributions of potential and density mean-values and oscillations in the ECRH and NBI plasmas at the TJ-II stellarator
(2022) Melnikov A. V.; Eliseev, L. G.; Drabinskiy, M. A.; Khabanov, P. O.; Мельников, Александр Владимирович
2D plasma potential φ distribution was measured in the electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI) plasmas of the TJ-II stellarator with the heavy ion beam probe for the whole radial range and wide area of the poloidal angle, and supported by Langmuir probe data at the edge. The whole operation domain for the on-axis ECRH was explored (n¯e = 0.45-0.8 ×1019 m-3, P EC = 220-470 kW), in addition, NBI plasmas with n¯e = 0.9-1.3 × 1019 m-3 and P NBI = 510 kW were studied. In ECRH plasmas the density ramp-up is accompanied by the evolution of the potential from the bell-like to the Mexican hat profile, while the density profiles were flat or slightly hollow. The potential has the positive peak at the centre, and LFS-HFS (low field - high field sides) and up-down symmetry. Equipotential lines are consistent with vacuum magnetic flux surfaces. In the high-density NBI scenario, the φ profile was fully negative with a minimum up to -300 V at the centre, while at low-density ECRH plasma, φ has a maximum up to +0.9 kV at the centre. Fluctuations of potential and density are stronger in low-density scenarios and not poloidally symmetric. At the mid-radius (area of the maximum density), root mean square (RMS) of fluctuations were up to φ ∼15 V at LFS vs ∼20 V at HFS; RMS n e ∼2% at LFS vs ∼3% at HFS. In the NBI plasmas with the density rise, the asymmetry decreases and finally vanishing at n¯e = 1.2 × 1019 m-3. 2D distribution of the NBI-induced Alfvén eigenmodes (AEs) shows asymmetric ballooning structure: contrary to broadband turbulence, AE-associated potential perturbation dominates in the LFS with a factor up to 1.7 respect to the HFS. The electrostatic mode, excited in ECRH plasmas by suprathermal electrons also shows asymmetric structures: density perturbation dominates in the top-bottom direction compared to LFS-HFS direction. © 2022 IOP Publishing Ltd.
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Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas
(2022) Hidalgo, C.; Ascasibar, E.; Alegre, D.; Alonso, A.; Melnikov, A. V.; Мельников, Александр Владимирович
© EURATOM 2022.TJ-II stellarator results on modelling and validation of plasma flow asymmetries due to on-surface potential variations, plasma fuelling physics, Alfvén eigenmodes (AEs) control and stability, the interplay between turbulence and neoclassical (NC) mechanisms and liquid metals are reported. Regarding the validation of the neoclassically predicted potential asymmetries, its impact on the radial electric field along the flux surface has been successfully validated against Doppler reflectometry measurements. Research on the physics and modelling of plasma core fuelling with pellets and tracer encapsulated solid pellet injection has shown that, although post-injection particle radial redistributions can be understood qualitatively from NC mechanisms, turbulence and fluctuations are strongly affected during the ablation process. Advanced analysis tools based on transfer entropy have shown that radial electric fields do not only affect the radial turbulence correlation length but are also capable of reducing the propagation of turbulence from the edge into the scrape-off layer. Direct experimental observation of long range correlated structures show that zonal flow structures are ubiquitous in the whole plasma cross-section in the TJ-II stellarator. Alfvénic activity control strategies using ECRH and ECCD as well as the relation between zonal structures and AEs are reported. Finally, the behaviour of liquid metals exposed to hot and cold plasmas in a capillary porous system container was investigated.
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Организационная единица
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.
Описание
Гибкий Heliac TJ-II был разработан на основе расчетов, выполненных командой физиков и инженеров CIEMAT в сотрудничестве с Национальной лабораторией Ок-Ридж (ORNL, США) и Институтом физики плазмы Макса Планка (IPP, Германия). Проект TJ-II получил преференциальную поддержку Европейского сообщества по атомной энергии (ЕВРАТОМ) для фазы I (физика) в 1986 году и для фазы II (инженерия) в 1990 году. Конструкция этого гибкого гелиака осуществлялась по частям в соответствии с к его составным элементам, которые были переданы в эксплуатацию различным европейским компаниям, хотя 60% инвестиций вернулись к испанским компаниям. TJ-II — третье устройство магнитного удержания в серии. В 1983 году аппарат TJ-I был принят в эксплуатацию. Название этого устройства связано с аббревиатурой «Токамак де ла Юнта де Энергия Ядерная энергия», это прежнее наименование CIEMAT . Аббревиатура сохранялась для последующих устройств по административным причинам.