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10 results on '"I.S. Nedzelskiy"'

1. Mass-Sensitive Ion Probe for Plasma Boundary Characterization on the Tokamak ISTTOK

Author

Horacio Fernandes, P. Duarte, I.S. Nedzelskiy, and Carlos A. Silva

Subjects
Spectrum analyzer, Materials science, Tokamak, Plasma, Condensed Matter Physics, Ion, law.invention, Magnetic field, Physics::Plasma Physics, law, Excited state, Atomic physics, ISTTOK, Voltage
Abstract

The principle of the mass-sensitive ion probe (MSIP) operation consists in a time-of-flight (TOF) analysis of the ions in the burst excited by a short (µ s-range) voltage pulse applied to a small grid immersed into the plasma. The ions in the burst propagate along the magnetic field lines of the tokamak with velocities determined by the value of the applied voltage and by the ions mass/charge (mi /Zi) ratio. The ions of different species and charges separated along some distance (TOF path) from the grid are detected by a retarding field energy analyzer (RFEA). This paper presents description of the MSIP design and first operation on the tokamak ISTTOK. The preliminary results of the obtained mass-spectra are presented and discussed (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Published
2010
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2. High-Intensity Thermionic Alkali Ion Sources for Plasma Diagnostics

Author

A.S. Kozachek, A.V. Melnikov, L. I. Krupnik, A.D. Komarov, and I.S. Nedzelskiy

Subjects
Nuclear and High Energy Physics, Tokamak, Materials science, Plasma parameters, Plasma, Condensed Matter Physics, Ion source, Ion, law.invention, Physics::Plasma Physics, law, Plasma parameter, Physics::Accelerator Physics, Plasma diagnostics, Atomic physics, ISTTOK
Abstract

The beam probing is widely used for the investigations of hot plasmas in thermonuclear devices. This diagnostic provides not disturbing local measurements of several plasma parameters such as the plasma density, the electron temperature, the plasma potential, and the magnetic field distributions. The atomic or ionic beams are injected into the plasma, and the secondary fluxes of ions of higher charge states or excited light radiation created during collisions with plasma particles are detected outside the plasma device. The physical characteristics of these secondary fluxes present the data for the plasma-parameter measurements. The injectors of probing beams should provide the beams of high intensity for clear discrimination of secondary signals. The ion source is the heart of any diagnostic injector. Among a variety of ion sources, the sources with solid-state thermionic emitters are commonly used in a heavy ion beam probe (HIBP) and different beam emission spectroscopy (BES) diagnostics due to their advantages in operation, such as simplicity, high enough emissivity, and capacity. This paper summarizes the results of development and investigations of the alkali (Li+, Na+, K+, and Cs+) and alkalilike (Tl+) thermionic ion sources with the beam current densities up to 4 mA/cm2 and the emitter capacities up to 5-6 mA ldr h/cm2. These ion sources are in use on currently operating injectors of HIBP (tokamaks: T-10, TUMAN-3M, and ISTTOK; stellarators: TJ-II and WEGA) and BES (ASDEX-U tokamak) diagnostics.

Published
2008
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3. Overview of TJ-II experiments

Author

J. Sánchez, M. Acedo, A. Alonso, J. Alonso, P. Alvarez, F. de Aragón, E. Ascasíbar, A. Baciero, R. Balbín, L. Barrera, E. Blanco, J. Botija, B. Brañas, E. de la Cal, E. Calderón, I. Calvo, A. Cappa, J.A. Carmona, B.A. Carreras, R. Carrasco, F. Castejón, G. Catalán, A.A. Chmyga, N.B. Dreval, M. Chamorro, S. Eguilior, J. Encabo, L. Eliseev, T. Estrada, A. Fernández, R. Fernández, J.A. Ferreira, J.M. Fontdecaba, C. Fuentes, J. de la Gama, A. García, L. García, I. García-Cortés, J.M. García-Regaña, B. Gonçalves, J. Guasp, J. Herranz, A. Hidalgo, C. Hidalgo, R. Jiménez-Gómez, J.A. Jiménez, D. Jiménez, I. Kirpitchev, A.D. Komarov, A.S. Kozachok, L. Krupnik, F. Lapayese, M. Liniers, D. López-Bruna, A. López-Fraguas, J. López-Rázola, A. López-Sánchez, E. de la Luna, G. Marcon, F. Martín, L. Martínez-Fresno, K.J. McCarthy, F. Medina, M. Medrano, A.V. Melnikov, P. Méndez, E. Mirones, B. van Milligen, I.S. Nedzelskiy, M. Ochando, J. Olivares, R. Orozco, P. Ortiz, J.L. de Pablos, L. Pacios, I. Pastor, M.A. Pedrosa, A. de la Peña, A. Pereira, D. Pérez-Risco, A. Petrov, S. Petrov, A. Portas, D. Rapisarda, L. Ríos, C. Rodríguez, L. Rodríguez-Rodrigo, E. Rodríguez-Solano, J. Romero, A. Ros, A. Salas, E. Sánchez, M. Sánchez, E. Sánchez-Sarabia, X. Sarasola, K. Sarksian, C. Silva, S. Schchepetov, N. Skvortsova, A. Soleto, F. Tabarés, D. Tafalla, J. Tera, A. Tolkachev, V. Tribaldos, V.I. Vargas, J. Vega, G. Velasco, M. Weber, G. Wolfers, S.J. Zweben, and B. Zurro

Subjects
Nuclear and High Energy Physics, Condensed Matter Physics
Published
2007
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4. Electron internal transport barriers, rationals and quasi-coherent oscillations in the stellarator TJ-II

Author

I Vargas, Alberto Alonso, L. I. Krupnik, V. I. Tereshin, Yu Tashev, J.L. de Pablos, C. Hidalgo, A.V. Melnikov, L A Pereira, A.D. Komarov, I.S. Nedzelskiy, L.G. Eliseev, A. S. Kozachok, T. Estrada, N. B. Dreval, and A.A. Chmyga

Subjects
Physics, Annihilation, Cyclotron, Magnetic confinement fusion, Electron, Condensed Matter Physics, law.invention, Core (optical fiber), Nuclear Energy and Engineering, Physics::Plasma Physics, law, Electron temperature, Plasma diagnostics, Atomic physics, Stellarator
Abstract

The evolution of core quasi-coherent modes has been investigated during the formation of electron internal transport barriers (e-ITB) in the TJ-II stellarator. These modes have been characterized using heavy ion beam probe and electron cyclotron emission diagnostics. The quasi-coherent mode evolves during formation/annihilation of the e-ITB and vanishes as the transport barrier is fully developed. These observations can be interpreted in terms of the influence of sheared flows in the stability of quasi-coherent modes.

Published
2005
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5. Overview of TJ-II experiments

Author

C Hidalgo, C Alejaldre, A Alonso, J Alonso, L Almoguera, F. de Aragón, E Ascasíbar, A Baciero, R Balbín, E Blanco, J Botija, B Brañas, E Calderón, A Cappa, J.A Carmona, R Carrasco, F Castejón, J.R Cepero, A.A Chmyga, J Doncel, N.B Dreval, S Eguilior, L Eliseev, T Estrada, J.A Ferreira, A Fernández, J.M Fontdecaba, C Fuentes, A García, I García-Cortés, B Gonçalves, J Guasp, J Herranz, A Hidalgo, R Jiménez, J.A Jiménez, D Jiménez-Rey, I Kirpitchev, S.M Khrebtov, A.D Komarov, A.S Kozachok, L Krupnik, F Lapayese, M Liniers, D López-Bruna, A López-Fraguas, J López-Rázola, A López-Sánchez, E. de la Luna, G Marcon, R Martín, K.J McCarthy, F Medina, M Medrano, A.V Melnikov, P Méndez, B. van Milligen, I.S Nedzelskiy, M Ochando, O Orozco, J.L. de Pablos, L Pacios, I Pastor, M.A Pedrosa, A. de la Peña, A Pereira, A Petrov, S Petrov, A Portas, D Rapisarda, L Rodríguez-Rodrigo, E Rodríguez-Solano, J Romero, A Salas, E Sánchez, J Sánchez, M Sánchez, K Sarksian, C Silva, S Schchepetov, N Skvortsova, F Tabarés, D Tafalla, A Tolkachev, V Tribaldos, I Vargas, J Vega, G Wolfers, and B Zurro

Subjects
Nuclear and High Energy Physics, Condensed Matter Physics
Published
2005
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6. Confinement and stability on the TJ-II stellarator

Author

A. Cappa, J R Cepero, E. de la Luna, Kieran J. McCarthy, A. López-Sánchez, K. Likin, L Rodríguez-Rodrigo, S. Schchepetov, A Salas, C. Hidalgo, L. I. Krupnik, E. Sánchez, A.V. Melnikov, J.A. Jiménez, R. Carrasco, B. Brañas, M. Liniers, E. Blanco, J.A. Romero, C. Fuentes, J. Herranz, Enrique Ascasibar, J. Guasp, C Alejaldre, I. Kirpitchev, M. A. Pedrosa, B. van Milligen, M Blaumoser, A. de la Peña, Jesús Vega, A.A. Chmyga, F. Medina, P. Méndez, M. A. Ochando, L.G. Eliseev, R. Balbín, B. Zurro, Angela Garcia, Francisco Castejón, B. Gonçalves, A. Hidalgo, S. Petrov, J. Sanchez, C F A Varandas, Ángela Fernández, A. Portas, Victor Tribaldos, D. López-Bruna, A. E. Petrov, J Doncel, J. López-Razola, A. S. Kozachok, L. Pacios, K. Sarksian, O. I. Fedyanin, I. García-Cortés, A. Baciero, S. M. Khrebtov, I.S. Nedzelskiy, M. Medrano, I. Pastor, Francisco L. Tabarés, F. Lapayese, D. Tafalla, J M Fontdecaba, T. Estrada, N. B. Dreval, A. Malaquias, A. D. Komarov, Nina N. Skvortsova, A. López-Fraguas, L Almoguera, Romualdo Martín, S Eguilior, J. A. Alonso, and J. Botija

Subjects
Materials science, Turbulence, Magnetic confinement fusion, Plasma, Condensed Matter Physics, Stability (probability), law.invention, Shear (sheet metal), Core (optical fiber), Coupling (physics), Nuclear Energy and Engineering, Physics::Plasma Physics, law, Physics::Space Physics, Atomic physics, Stellarator
Abstract

This paper describes a series of experiments performed in TJ-II stellarator with the aim of studying the influence of magnetic configuration on stability and transport properties of TJ-II plasmas. Plasma potential profiles have been measured in several configurations up to the plasma core with the heavy ion beam probe diagnostic. Low-order rational surfaces have been positioned at different plasma radii observing the effect on transport features. Plasma edge turbulent transport has been studied in configurations that are marginally stable due to decreased magnetic well. Results show a dynamical coupling between gradients and turbulent transport. Experiments on the influence of magnetic shear on confinement are reported. Global confinement issues as well as enhanced confinement regimes found in TJ-II are discussed as well.

Published
2002
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7. Dynamics of flows and confinement in the TJ-II stellarator

Author

Juan Miguel Insúa Arévalo, Enrique Ascasibar, S. Petrov, A. Martin, M. A. Pedrosa, L. I. Krupnik, A. Cappa, E. Oyarzábal, E. Sánchez, R. Carrasco, J. Hernández, E. R. Solano, A. E. Petrov, A. S. Kozachok, A.D. Komarov, Ralf Kleiber, J. López-Razola, D. López-Bruna, A. Tolkachev, M. Sánchez, E. Sánchez-Sarabia, A. de la Peña, G. Velasco, Kieran J. McCarthy, J.A. Sebastián, A. Soleto, Roman Hatzky, J. Vega, M. Navarro, J. Hernanz, M. A. Ochando, C. Hidalgo, D. Tafalla, P. Méndez, I. Kirpitchev, José Luis Velasco, B. J. Sun, I.S. Nedzelskiy, Luis Garcia, F. Martín-Hernández, J. Martínez-Fernández, M. Medrano, I. Pastor, Carlos A. Silva, Marley Vanegas Chamorro, M. Borchardt, J.A. Jiménez, A. Pereira, C. Rodríguez, A. Baciero, P. Álvarez, P. Monreal, F. Fernández, K. Sarksian, A. Alonso, L. Ríos, J. Herranz, Francisco L. Tabarés, P. García-Sánchez, F. Lapayese, R. García-Gómez, A. Bustos, A. Jiménez-Denche, D. Carralero, D. Alegre, B. van Milligen, J. Sánchez, L. Pacios, M. Tereshchenko, L.G. Eliseev, J. Olivares, L. Melón, A. Portas, J. A. Alonso, E. de la Cal, J. M. Fontdecaba, A.V. Melnikov, E. Blanco, A.A. Chmyga, J. Botija, T. Estrada, J.A. Romero, Ivan Calvo, J.L. de Pablos, R. Castro, Francisco Castejón, B. Rojo, E. Rincón, G. Catalán, G. Wolfers, F. Martín-Díaz, F. Medina, A. López-Fraguas, M. Liniers, S. da Graca, A.B. Martín-Rojo, B. Zurro, A. Ros, J. Guasp, and D. Baiao

Subjects
Physics, Nuclear and High Energy Physics, Work (thermodynamics), Turbulence, Flow (psychology), Observable, Mechanics, Condensed Matter Physics, law.invention, Physics::Fluid Dynamics, Viscosity, law, Relaxation (physics), Statistical physics, Shear flow, Stellarator
Abstract

This work deals with the results on flow dynamics in TJ-II plasmas under Li-coated wall conditions, which produces low recycling and facilitates the density control and access to improved confinement transitions. The low-density transition, characterized by the emergence of the shear flow layer, is described from first principles and within the framework of neoclassical theory. The vanishing of the neoclassical viscosity when approaching the transition from below explains the observation of a number of turbulent phenomena reported in TJ-II in recent years; a unifying picture is provided in which zonal, i.e. large scale, radially structured, perturbations are observable when the neoclassical damping is sufficiently small. Preliminary linear, collisionless gyrokinetic simulations are carried out to assess that the measured time scale of relaxation of such perturbations is reasonably understood theoretically. In higher density regimes, the physical mechanisms behind the L–H transition have been experimentally studied. The spatial, temporal and spectral structure of the interaction between turbulence and flows has been studied close to the L–H transition threshold conditions. The temporal dynamics of the turbulence-flow interaction displays a predator–prey relationship and both radial outward and inward propagation velocities of the turbulence-flow front have been measured. Finally, a non-linear relation between turbulent fluxes and gradients is observed.

Published
2013

8. Overview of TJ-II experiments

Author

T. Madeira, G. Wolfers, J. López-Razola, A.V. Melnikov, A. Molinero, E. Blanco, A. Baciero, J. Martínez-Fernández, P. Álvarez, F. Martín-Díaz, Luis Garcia, F. Medina, J. Olivares, A. Soleto, E. Rincón, M. Weber, J. Vega, A. Alonso, I.S. Nedzelskiy, A. Petrov, M. Medrano, I. Pastor, Carlos A. Silva, G. Catalán, G. Sánchez-Burillo, J.A. Romero, J.A. Jiménez, A. Pereira, M. Acedo, A. Portas, D. Tafalla, L. Pacios, A. Cappa, A. Tolkachev, P. Méndez, J.A. Sebastián, J. A. Alonso, F. Martín-Hernández, S. Petrov, E. de la Cal, Francisco Castejón, Marley Vanegas Chamorro, B. Zurro, E. Oyarzábal, C. Rodríguez, L. Esteban, Jorge Ferreira, D. Alegre, R. Jiménez-Gómez, A. Ros, M. Liniers, A. S. Kozachok, A.B. Martín-Rojo, J. M. Garcia-Regana, S. González, B. Rojo, R. García-Gómez, E. R. Solano, J. Hernanz, J. Botija, T. Happel, J. Guasp, A. D. Komarov, I. Kirpitchev, K. Sarksian, D. Baiao, Juan Miguel Insúa Arévalo, Ivan Calvo, J.M. Fontdecaba, José Luis Velasco, Benjamin A. Carreras, Antonio Gómez-Iglesias, P. García-Sánchez, A.A. Chmyga, Francisco L. Tabarés, F. Lapayese, T. Estrada, J. M. Reynolds, L. Melón, J. Sanchez, J. Tera, J. Herranz, A. Bustos, G.A. Rattá, D. Carralero, B. van Milligen, M. Navarro, M. A. Ochando, A. López-Fraguas, D. López-Bruna, A. de la Peña, R. Castro, L. I. Krupnik, E. Sánchez, R. Carrasco, M. Sánchez, G. Velasco, E. Mirones, J.L. de Pablos, Enrique Ascasibar, M. A. Pedrosa, A. Jiménez-Denche, L.G. Eliseev, E. Sánchez-Sarabia, L. Barrera, Kieran J. McCarthy, C. Hidalgo, and L. Ríos

Subjects
Physics, Nuclear and High Energy Physics, Turbulence, Magnetic confinement fusion, Mechanics, Plasma, Condensed Matter Physics, law.invention, Coupling (physics), Physics::Plasma Physics, law, Electric field, Physics::Space Physics, Limiter, Atomic physics, Topology (chemistry), Stellarator
Abstract

This paper presents an overview of experimental results and progress made in investigating the link between magnetic topology, electric fields and transport in the TJ-II stellarator. The smooth change from positive to negative electric field observed in the core region as the density is raised is correlated with global and local transport data. A statistical description of transport is emerging as a new way to describe the coupling between profiles, plasma flows and turbulence. TJ-II experiments show that the location of rational surfaces inside the plasma can, in some circumstances, provide a trigger for the development of core transitions, providing a critical test for the various models that have been proposed to explain the appearance of transport barriers in relation to magnetic topology. In the plasma core, perpendicular rotation is strongly coupled to plasma density, showing a reversal consistent with neoclassical expectations. In contrast, spontaneous sheared flows in the plasma edge appear to be coupled strongly to plasma turbulence, consistent with the expectation for turbulent driven flows. The local injection of hydrocarbons through a mobile limiter and the erosion produced by plasmas with well-known edge parameters opens the possibility of performing carbon transport studies, relevant for understanding co-deposit formation in fusion devices.

Published
2011
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9. Confinement transitions in TJ-II under Li-coated wall conditions

Author

J.L. de Pablos, Francisco Castejón, R. Fernández-Gavilán, Victor Tribaldos, G. Catalán, V. I. Vargas, Marley Vanegas Chamorro, David Rapisarda, R. Balbín, E. Mirones, J. Botija, A. S. Kozachok, K. Sarksian, L. Esteban, R. Carrasco, G. Marcon, I. García-Cortés, A.D. Komarov, S. E. Lysenko, J.A. Jiménez, A. Pereira, J. Sánchez, J. A. Alonso, J. M. Carmona, E. Rincón, J. Hernanz, J. Tera, J. Herranz, A.A. Chmyga, M. Acedo, B. Zurro, José Luis Velasco, C. Rodríguez, Alfonso Tarancón, D. Jiménez-Rey, R. Castro, C. Fuentes, A. Ros, Enrique Ascasibar, F. Martín, L. Ríos, A. de la Peña, Jorge Ferreira, D. Tafalla, A. Tolkachev, Luis Garcia, D. Carralero, B. van Milligen, Yu.I. Taschev, M. Sánchez, G. Velasco, Ángela Fernández, L. I. Krupnik, A. Baciero, P. Álvarez, M. Liniers, M. A. Pedrosa, E. de la Cal, Ivan Calvo, A. Cappa, A. Jiménez-Denche, J. M. Fontdecaba, A. Soleto, J. M. Garcia-Regana, Nina N. Skvortsova, J. Vega, E. Sánchez, L. Pacios, A. de Bustos, T. Happel, D. López-Bruna, V. Maurin, T. Estrada, S. Petrov, P. Méndez, D. Pérez-Risco, J. Guasp, J.A. Sebastián, J. M. Reynolds, Alberto Alonso, G.A. Rattá, E. Sánchez-Sarabia, L.G. Eliseev, A.V. Melnikov, R. Jiménez-Gómez, A. López-Sánchez, A. Portas, Benjamin A. Carreras, M. A. Ochando, M. Weber, L. Barrera, Kieran J. McCarthy, E. Blanco, J. Olivares, G. Wolfers, D. G. Pretty, L. Guimarais, A Salas, German Perez, Francisco L. Tabarés, F. Lapayese, C. Hidalgo, F. Medina, A. López-Fraguas, J.A. Romero, E. R. Solano, I. Kirpitchev, S. Schchepetov, R. García-Gómez, I.S. Nedzelskiy, A. Petrov, M. Medrano, I. Pastor, Carlos A. Silva, and J. López-Razola

Subjects
Nuclear and High Energy Physics, Materials science, Density gradient, chemistry.chemical_element, Plasma, Condensed Matter Physics, Thermal diffusivity, Evaporation (deposition), law.invention, Ion, Vacuum evaporation, chemistry, law, Lithium, Atomic physics, Stellarator
Abstract

This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma–wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z, Li was chosen because there exists a reactor-oriented interest in this element, thus giving special relevance to the investigation of its properties. The Li-coating has led to important changes in plasma performance. Particularly, the effective density limit in NBI plasmas has been extended reaching central values of 8 × 1019 m−3 and T e ≈ 250–300 eV, with peaked density, rather flat T e profiles and higher ion temperatures. Due to the achieved density control, a second type of transition has been added to the low density ones previously observed in ECRH plasmas: higher density transitions characterized by the fall in Hα emission, the onset of steep density gradient and the reduction in the turbulence; which are characteristics of transition to the H mode. Confinement studies in ECH plasmas indicate that lowest order magnetic resonances, even in a low shear environment, locally reduce the effective electron heat diffusivities, while Alfven eigenmodes destabilized in NBI plasmas can influence fast ion confinement.

10. Investigation of the transition of multicycle AC operation in ISTTOK under edge electrode biasing.

Author

A. Malaquias, R.B. Henriques, C. Silva, H. Figueiredo, I.S. Nedzelskiy, H. Fernandes, R. Sharma, and V.V. Plyusnin

Subjects
PLASMA electrodes, ALTERNATING currents, ELECTRONS, PLASMA density, MAGNETIC fields
Abstract

In this paper we present recent results obtained on plasma edge electrode biasing during AC discharges. The goal is to obtain experimental evidence on a number of plasma parameters that can play a role during the AC transition on the repeatability and reproducibility of AC operation. The control of the plasma density in the quiescent phase is made just before the AC transition by means of positive edge biasing leading to a transitory improved of density (30%–40%). Gas puff experiments show that the increase of background gas pressure during discharge led to a better success of the AC transition. The experimental results indicate that the increase of density during the AC transition induced by edge biasing is followed by an electron temperature drop. The drop in electron temperature leads in most cases the formation of runaway electrons. It has been observed that the runaway population during discharge flattop depends on the interplay between gas content and plasma density and temperature. The results also confirm that the correct balance of external magnetic fields is crucial during the AC transition phase where drift electron currents are formed. The results from the heavy ion beam diagnostic show that the formation of plasma current during consecutive AC transitions is asymmetric. Numerical simulations indicate that for some particular conditions this result could be reproduced from assuming the presence of two counter-currents during AC transition. [ABSTRACT FROM AUTHOR]

Published
2017
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