A. Bencze

8640809800

Publications - 22

Overview of the COMPASS results

W. Bin K. Bogár P. Bilkova P. Bohm O. Bogár I. Borodkina E. Gauthier S. Brezinsek P. Buratti J. Čaloud None Fuková J. Gerardin K. Kovarik J. P. Gunn M. Jirsa P. Junek A. Kallenbach O. Kovanda M. Gobbin G. Grenfell Y. Gribov N. Lemoine X. Litaudon Y. Q. Liu I. Mysiura D. I. Naydenkova F. Napoli J. K. Park N. Patel P. Pavlo M. Poradzinski J. Preinhaelter A. Prishvitsin A. Podolnik D. Réfy R. A. Pitts R. Roccella N. C. Logan T. Loarer A. Loarte P. Lourenco A. Casolari J. Adámek J. Horacek O. Grover R. Dejarnac J. Cavalier O. Ficker M. Hron M. Komm E. Macúšová C. Castaldo J. Čečrdle J. Čeřovský E. Matveeva R. Pánek M. Peterka J. Seidl D. Cipciar S. Entler M. Farník H. Fernandes M. Dimitrova I. Ďuran D. Fridrich M. Grof L. Kripner A. Devitre L. Krlín P. Kulhánek M. Lehnen S. Lukes T. Markovic P. Mácha A. Marin Roldan M. Rabinski J. Matějíček J. Mlynar D. Sestak G. Mazzitelli P. Hacek J. Krbec F. Brochard M. Berta A. Bencze D. Tskhakaya V. Yanovskiy F. J. Artola S. Atikukke P. Barton J. Havlicek A. Havranek C. Hidalgo K. Hromasová O. Hronova M. Iafrati N. Isernia F. Jaulmes M. Imrišek M. Jeřáb

Publication Name: Nuclear Fusion

Publication Date: 2022-04-01

Volume: 62

Issue: 4

Page Range: Unknown

Description:

COMPASS addressed several physical processes that may explain the behaviour of important phenomena. This paper presents results related to the main fields of COMPASS research obtained in the recent two years, including studies of turbulence, L-H transition, plasma material interaction, runaway electron, and disruption physics: Tomographic reconstruction of the edge/SOL turbulence observed by a fast visible camera allowed to visualize turbulent structures without perturbing the plasma. Dependence of the power threshold on the X-point height was studied and related role of radial electric field in the edge/SOL plasma was identified. The effect of high-field-side error fields on the L-H transition was investigated in order to assess the influence of the central solenoid misalignment and the possibility to compensate these error fields by low-field-side coils. Results of fast measurements of electron temperature during ELMs show the ELM peak values at the divertor are around 80% of the initial temperature at the pedestal. Liquid metals were used for the first time as plasma facing material in ELMy H-mode in the tokamak divertor. Good power handling capability was observed for heat fluxes up to 12 MW m-2 and no direct droplet ejection was observed. Partial detachment regime was achieved by impurity seeding in the divertor. The evolution of the heat flux footprint at the outer target was studied. Runaway electrons were studied using new unique systems - impact calorimetry, carbon pellet injection technique, wide variety of magnetic perturbations. Radial feedback control was imposed on the beam. Forces during plasma disruptions were monitored by a number of new diagnostics for vacuum vessel (VV) motion in order to contribute to the scaling laws of sideways disruption forces for ITER. Current flows towards the divertor tiles, incl. possible short-circuiting through PFCs, were investigated during the VDE experiments. The results support ATEC model and improve understanding of disruption loads.

Open Access: Yes

DOI: 10.1088/1741-4326/ac301f

Technical upgrade and first tests of the experimental device for quasi-2D turbulent electrolyte flow experiment

M. Berta L. Bardóczi E. Walcz L. Poszovecz A. Biricz A. Bencze

Publication Name: Fusion Engineering and Design

Publication Date: 2019-09-01

Volume: 146

Issue: Unknown

Page Range: 1899-1902

Description:

A major upgrade of the experimental device for quasi-2 dimensional turbulence studies in magnetized electrolyte system is presented. The development has been motivated by the preparation of envisaged new experiments to investigate the effect of boundary walls on 2D turbulence cascades and the study of small vortex interactions with large scale sheared flows. The latter problem is relevant in different basic scientific as well as applied areas such as the reduction of anomalous transport via shear flows in magnetically confined fusion plasmas. The hardware upgrade consists of: (a) significantly larger electrolyte tank able to accommodate up to 2500 permanent magnets and adjustable walls, (b) ensemble of an electronically driven solenoid and a configurable permanent magnet array, (c) highly automatic acquisition and control of the experimental data and parameters. A first experimental test of the upgraded device is also presented.

Open Access: Yes

DOI: 10.1016/j.fusengdes.2019.03.060

Characterization of edge and scrape-off layer fluctuations using the fast Li-BES system on COMPASS

M. Berta P. Hacek J. Krbec M. Szutyányi A. Buzás A. Bencze

Publication Name: Plasma Physics and Controlled Fusion

Publication Date: 2019-06-21

Volume: 61

Issue: 8

Page Range: Unknown

Description:

Recently the Lithium-Beam Emission Spectroscopy (Li-BES) system on COMPASS has reached its full diagnostic power in terms of routine automatic operation in any kind of plasma scenarios and it is normally used as a standard tool for reconstruction of ultra fast density profiles in the edge region of COMPASS plasmas. The purpose of this study is to investigate the advantages and limitations of the COMPASS Li-BES system in characterizing plasma electron density fluctuations. We show how the atomic physics of plasma-beam interactions can affect the interpretation of the measurement at different radial positions and for different electron density profiles. We also demonstrate the usability of generalized sequential probability ratio test for automatic event detection. Using non-perturbative diagnostic, we verify the validity of the stochastic Garcia-model for scrape-off layer filaments and accompanying holes (density deficits).

Open Access: Yes

DOI: 10.1088/1361-6587/ab24a0

Plasma edge current fluctuation measurements during the ELM cycle with the atomic beam probe at COMPASS

M. Berta G. Anda D. Dunai P. Hacek D. Réfy M. Aradi J. Krbec S. Zoletnik A. Bencze

Publication Name: 46th Eps Conference on Plasma Physics Eps 2019

Publication Date: 2019-01-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

No description provided

Open Access: Yes

DOI: DOI not available

Automatic ELM detection and study of statistical ELM properties by Li-BES on COMPASS

M. Berta P. Hacek J. Krbec M. Szutyányi R. Somers M. Hron R. Pánek A. Bencze V. Weinzettl

Publication Name: 46th Eps Conference on Plasma Physics Eps 2019

Publication Date: 2019-01-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

No description provided

Open Access: Yes

DOI: DOI not available

Development of an ion beam detector for the atomic beam probe diagnostic

M. Berta G. Anda D. Dunai P. Hacek D. Réfy M. Aradi J. Krbec R. Pánek S. Zoletnik A. Bencze V. Weinzettl J. Stockel

Publication Name: Review of Scientific Instruments

Publication Date: 2018-11-01

Volume: 89

Issue: 11

Page Range: Unknown

Description:

The atomic beam probe diagnostic concept aims at measuring the edge magnetic field and through that edge current distribution in fusion plasmas by observing trajectories of an ion beam stemming from a diagnostic neutral beam. The diagnostic potentially has microsecond scale time resolution and can thus prove to be a powerful option to study fast changes in the edge plasma. A test detector has been installed on the COMPASS tokamak as an extension of the existing lithium beam diagnostic system. It employs a relatively simple concept of an array of conductive detection plates measuring the incident ion current, which is then amplified and converted to a voltage signal. The aim of the test detector is to experimentally examine the idea of the diagnostic and provide background data for design and installation of a final detector. Also, a numerical code based on the CUDA parallel computing platform has been developed for modeling lithium ion trajectories in the given COMPASS plasma discharges. We present the developments of the detector design and test measurements of the diagnostic performed both in a laboratory beam system and on the COMPASS tokamak.

Open Access: Yes

DOI: 10.1063/1.5044529

Advanced neutral alkali beam diagnostics for applications in fusion research (invited)

D. Réfy B. Tál G. Petravich G. I. Pokol M. Vécsei G. Anda D. Dunai M. Aradi O. Asztalos S. Bató G. Demeter S. Hegedus P. Hacek M. Berta A. Bencze T. Krizsanóczi M. Lampert G. H. Hu D. Nagy J. Németh M. Otte S. Zoletnik

Publication Name: Review of Scientific Instruments

Publication Date: 2018-10-01

Volume: 89

Issue: 10

Page Range: Unknown

Description:

Diagnosing the density profile at the edge of high temperature fusion plasmas by an accelerated lithium beam is a known technique since decades. By knowledge of the relevant atomic physics rate coefficients, the plasma electron density profile can be calculated from the relatively calibrated light profile along the beam. Several additional possibilities have already been demonstrated: Charge Exchange Resonance Spectroscopy (CXRS) for ion temperature/flow and Zeeman polarimetry for edge plasma current; therefore the Li-beam diagnostic offers a wealth of information at the plasma edge. The weaknesses of the method are the relatively faint light signal, background light, and technical difficulties of the beam injector which usually seriously limit the applicability. In this talk, we present systematic developments in alkali-beam diagnostics (Li, Na) for the injector and the observation system and detectors which resulted in strongly increased capabilities. Advanced systems have been built, and microsecond scale density profile, turbulence, and zonal flow measurement have been demonstrated. A novel edge current measurement technique has also been designed, and components have been tested with potential microsecond-scale time resolution. Additional possibilities of these advanced systems for spectral measurements (CXRS and various Zeeman schemes) are also discussed.

Open Access: Yes

DOI: 10.1063/1.5039309

Statistical analysis of SOL fluctuations on COMPASS tokamak as measured by the Li-BES diagnostic

M. Berta J. Seidl P. Hacek J. Krbec A. Buzás R. Pánek A. Bencze

Publication Name: 45th Eps Conference on Plasma Physics Eps 2018

Publication Date: 2018-01-01

Volume: 2018-July

Issue: Unknown

Page Range: 849-852

Description:

No description provided

Open Access: Yes

DOI: DOI not available

Atomic Beam Probe diagnostic for plasma edge current measurements at COMPASS

M. Berta G. Anda D. Dunai P. Hacek D. Réfy M. Aradi M. Lampert J. Krbec M. Palánkai S. Hegedus B. Leskó J. Kádi D. Nagy R. Pánek S. Zoletnik A. Bencze V. Weinzettl

Publication Name: 45th Eps Conference on Plasma Physics Eps 2018

Publication Date: 2018-01-01

Volume: 2018-July

Issue: Unknown

Page Range: 1028-1031

Description:

No description provided

Open Access: Yes

DOI: DOI not available

Automatic ELM detection using gSPRT on the COMPASS tokamak

M. Berta M. Szutyányi M. Hron R. Pánek A. Bencze

Publication Name: Fusion Engineering and Design

Publication Date: 2017-11-01

Volume: 123

Issue: Unknown

Page Range: 950-954

Description:

This paper contains the description of the generalized Sequential Probability Ratio Test (gSPRT) method used for automatic ELM detection in different diagnostic signals collected on the COMPASS tokamak. After determination of H-mode region based on Dα signal in a given shot, ELMs are automatically detected in different diagnostic time traces (e.g. magnetic signals and also in Dα signals). The onset time, the maximum location and the peak value, and the duration of each detected ELM is determined. Analyzed diagnostic signals came from different radial positions of the studied plasma volume, thus from arrival times of given ELM into different detectors, the average radial propagation velocity of the ELM event can be also estimated. Comparison of results from gSPRT method with two different, commonly used automatic ELM detection method (threshold technique and correlation based technique) is also reported.

Open Access: Yes

DOI: 10.1016/j.fusengdes.2017.03.025

Lithium beam diagnostic system on the COMPASS tokamak

M. Berta G. Anda S. Bató D. Dunai T. Krizsanóczi T. Ilkei P. Hacek D. Réfy J. Krbec I. G. Kiss G. Veres S. Zoletnik A. Bencze

Publication Name: Fusion Engineering and Design

Publication Date: 2016-10-01

Volume: 108

Issue: Unknown

Page Range: 1-6

Description:

An improved lithium beam based beam emission spectroscopy system - installed on COMPASS tokamak - is described. The beam energy enhanced up to 120 keV for Atomic Beam Probe measurement. The size of the ion source is doubled, using a newly developed thermionic heater instead of the conventionally used heating (tungsten or molybdenum) filament. The neutralizer is also improved. It produces the same sodium vapor in a cell but minimize the loss condensing the vapor on a cold surface which is led back (in fluid state) into the sodium oven. This way we call it recirculating neutralizer. The observation system consists of a CCD camera and an avalanche photodiode array.

Open Access: Yes

DOI: 10.1016/j.fusengdes.2016.04.022

Li-BES detection system for plasma turbulence measurements on the COMPASS tokamak

M. Berta G. Anda D. Dunai P. Hacek D. Réfy A. Kovácsik J. Krbec M. Hron G. Veres R. Pánek S. Zoletnik A. Bencze V. Weinzettl

Publication Name: Fusion Engineering and Design

Publication Date: 2015-10-01

Volume: 96-97

Issue: Unknown

Page Range: 795-798

Description:

A new Li beam emission spectroscopy (Li-BES) diagnostic system with a ∼ cm spatial resolution, and with beam energy ranging from 10 keV up to 120 keV and a 18 channel Avalanche photo diode (APD) detector system sampled at 2 MHz has been recently installed and tested on the COMPASS tokamak. This diagnostic allows to reconstruct density profile based on directly measured light profiles, and to follow turbulent behaviour of the edge plasma. The paper reports technical capabilities of this new system designed for fine spatio-temporal measurements of plasma electron density. Focusing on turbulence-induced fluctuation measurements, we demonstrate how physically relevant information can be extracted using the COMPASS Li-BES system.

Open Access: Yes

DOI: 10.1016/j.fusengdes.2015.06.030

Experimental confirmation of self-regulating turbulence paradigm in two-dimensional spectral condensation

M. Berta L. Bardóczi L. Schmitz A. Bencze

Publication Name: Physical Review E Statistical Nonlinear and Soft Matter Physics

Publication Date: 2014-12-03

Volume: 90

Issue: 6

Page Range: Unknown

Description:

Turbulent transport in magnetic fusion plasmas can be significantly suppressed by Reynolds-stress-induced zonal flows, allowing effective plasma confinement. We present experimental evidence of spatiotemporal correlation between small-scale turbulence-induced Reynolds stress and large-scale zonal flow production in the E×B driven hydrodynamic spectral condensation. We show that Reynolds stress is generated effectively by anisotropic vorticity structures possessing collective tilt angle. The maximum amplitude of the tilt, the Reynolds stress, and the mean zonal flow production coincide with the transition time of the velocity field, indicating a key role of turbulence-induced Reynolds stress in the condensation of the flow. The analysis of the energy transfer between turbulence and zonal flow shows coherent oscillations with π/2 phase delay, thus indicating a predator-prey-like interaction between zonal flow and turbulence.

Open Access: Yes

DOI: 10.1103/PhysRevE.90.063103

Plasma tomographic reconstruction from tangentially viewing camera with background subtraction

M. Berta G. Verdoolaege P. Hacek T. Odstrčil M. Odstrčil T. Szabolics J. Mlynar A. Bencze V. Weinzettl

Publication Name: Review of Scientific Instruments

Publication Date: 2014-01-01

Volume: 85

Issue: 1

Page Range: Unknown

Description:

Light reflections are one of the main and often underestimated issues of plasma emissivity reconstruction in visible light spectral range. Metallic and other specular components of tokamak generate systematic errors in the optical measurements that could lead to wrong interpretation of data. Our analysis is performed at data from the tokamak COMPASS. It is a D-shaped tokamak with specular metallic vessel and possibility of the H-mode plasma. Data from fast visible light camera were used for tomographic reconstruction with background reflections subtraction to study plasma boundary. In this article, we show that despite highly specular tokamak wall, it is possible to obtain a realistic reconstruction. The developed algorithm shows robust results despite of systematic errors in the optical measurements and calibration. The motivation is to obtain an independent estimate of the plasma boundary shape. © 2014 AIP Publishing LLC.

Open Access: Yes

DOI: 10.1063/1.4862652

Development of atomic beam probe for tokamaks

M. Berta G. Anda I. G. Kiss J. Havlicek S. Tulipán P. Hacek M. Aradi Cs Buday G. Veres S. Zoletnik A. Bencze

Publication Name: Fusion Engineering and Design

Publication Date: 2013-11-01

Volume: 88

Issue: 11

Page Range: 2875-2880

Description:

The concept and development of a new detection method for light alkali ions stemming from diagnostic beams installed on medium size tokamak is described. The method allows us the simultaneous measurement of plasma density fluctuations and fast variations in poloidal magnetic field, therefore one can infer the fast changes in edge plasma current. The concept has been worked out and the whole design process has been done at Wigner RCP. The test detector with appropriate mechanics and electronics is already installed on COMPASS tokamak. General ion trajectory calculation code (ABPIons) has also been developed. Detailed calculations show the possibility of reconstruction of edge plasma current density profile changes with high temporal resolution, and the possibility of density profile reconstruction with better spatial resolution compared to standard Li-BES measurement, this is important for pedestal studies. © 2013 Elsevier B.V.

Open Access: Yes

DOI: 10.1016/j.fusengdes.2013.05.064

Inverse energy cascade and turbulent transport in a quasi-two-dimensional magnetized electrolyte system: An experimental study

M. Berta L. Bardóczi A. Bencze

Publication Name: Physical Review E Statistical Nonlinear and Soft Matter Physics

Publication Date: 2012-05-30

Volume: 85

Issue: 5

Page Range: Unknown

Description:

We present an experimental study of the inverse energy cascade, spectral condensation, and turbulent particle transport in an electromagnetically driven thin layer of NaCl electrolyte. The presence of the bottom friction provides an energy sink at large scales for the turbulent flow. This energy sink crucially contributes to the balance of the forcing and dissipation which makes the inverse cascade steady. The present work provides an estimation of the linear dissipation rate on an experimental basis. We also show how the dissipation rate affects the characteristic features of the velocity spectrum and the dynamics of the spectral condensation. A quantitative study of the turbulent diffusion shows a significant decrease of the radial transport during the spectral condensation process. © 2012 American Physical Society.

Open Access: Yes

DOI: 10.1103/PhysRevE.85.056315

Concept of an atomic beam probe diagnostic on COMPASS tokamak

M. Berta G. Anda D. Dunai M. Aradi G. Veres S. Zoletnik A. Bencze

Publication Name: 36th Eps Conference on Plasma Physics 2009 Eps 2009 Europhysics Conference Abstracts

Publication Date: 2009-12-01

Volume: 33 E2

Issue: Unknown

Page Range: 1399-1402

Description:

No description provided

Open Access: Yes

DOI: DOI not available

On the statistics of ELM filaments measured by fast low field side wall Langmuir probes on TCV

M. Berta G. Veres R. A. Pitts O. E. Garcia A. Bencze

Publication Name: 34th Eps Conference on Plasma Physics 2007 Eps 2007 Europhysics Conference Abstracts

Publication Date: 2007-12-01

Volume: 31

Issue: 2

Page Range: 820-823

Description:

No description provided

Open Access: Yes

DOI: DOI not available

The spatial structure of flows, Reynolds stress and turbulence in the CASTOR tokamak

M. Berta R. Dejarnac B. Tál M. Hron J. Zajac S. Zoletnik A. Bencze J. Stockel

Publication Name: 33rd Eps Conference on Plasma Physics 2006 Eps 2006

Publication Date: 2006-12-01

Volume: 2

Issue: Unknown

Page Range: 1452-1455

Description:

No description provided

Open Access: Yes

DOI: DOI not available

Observation of zonal flow-like structures using the autocorrelation-width technique

M. Berta J. Adámek M. Hron S. Zoletnik A. Bencze J. Stockel

Publication Name: Plasma Physics and Controlled Fusion

Publication Date: 2006-04-01

Volume: 48

Issue: 4

Page Range: S137-S153

Description:

This paper presents the first application of the autocorrelation-width technique (Bencze A and Zoletnik S 2005 Phys. Plasmas 12 052323) to detect and characterize the microturbulence-zonal flow system using fluctuating signals ( , ) measured by arrays of single-tip Langmuir probes in the CASTOR tokamak. Radially localized (≈1 cm) random flow structures have been clearly observed with a lifetime of ≈1 ms and a long-range poloidal correlation, extending over at least one-fourth of the poloidal circumference. © 2006 IOP Publishing Ltd.

Open Access: Yes

DOI: 10.1088/0741-3335/48/4/S10

Detection of radially localized and poloidally symmetric structures in the poloidal flow of tokamak plasmas

M. Berta J. Adámek M. Hron S. Zoletnik A. Bencze J. Stockel

Publication Name: 32nd Eps Conference on Plasma Physics 2005 Eps 2005 Held with the 8th International Workshop on Fast Ignition of Fusion Targets Europhysics Conference Abstracts

Publication Date: 2005-12-01

Volume: 3

Issue: Unknown

Page Range: 1994-1997

Description:

No description provided

Open Access: Yes

DOI: DOI not available

Two-dimensional density and density fluctuation diagnostic for the edge plasma in fusion devices

M. Berta S. Fiedler G. Petravich J. Schweinzer K. McCormick S. Zoletnik A. Bencze

Publication Name: Review of Scientific Instruments

Publication Date: 2005-07-01

Volume: 76

Issue: 7

Page Range: Unknown

Description:

A technique is described for the two-dimensional measurement of electron density profile and fluctuations in edge regions of magnetically confined fusion plasmas. The method is based on existing lithium beam beam emission spectroscopy technique, two-dimensional resolution is achieved by electrostatically scanning the beam. If scanning is performed faster than the lifetime of the turbulent structures in the plasma, the diagnostic is capable of measuring the structure of electron density fluctuations as well. The beam strength of currently available beams makes the detection of single fluctuation events impossible, but the full two-dimensional spatial structure of correlations can still be determined. The article describes the technique and fast beam deflection tests up to 250 kHz. The capabilities of such a diagnostic for fluctuation measurement are explored by simulating measurement signals. Measurement of both the two-dimensional density profile, fluctuation correlation function and poloidal flow velocity are demonstrated at the Wendelstein 7-AS stellarator. The shape of the density profile, the radial and poloidal correlation lengths and the flow velocity are in agreement with expectations and previous Langmuir probe measurement. © 2005 American Institute of Physics.

Open Access: Yes

DOI: 10.1063/1.1947727