This paper reports recent experiments in the TJ-II stellarator using a dual Heavy Ion Beam probe diagnostic. The studies were focused on characterizing plasma potential profiles, investigating self-organization mechanisms and Alfven Eigenmodes (AEs). Results showed plasma equipotential measurements consistent with vacuum magnetic surfaces and the presence of zonal flows in the plasma core region. The investigation of Alfven Eigen modes showed their radial localization and poloidal asymmetries in potential and density fluctuations driven by AEs.

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.

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.

An overview describes the evolution of HIBP diagnostics from the origins till today. The progress in the beam technology is presented by examples of HIBPs in tokamaks and stellarators. At the beginning, HIBP provided timeaveraged measurements of plasma potential in single space location, then it evolves to time-resolved measurements of radial distributions and finally it becomes a multi-purpose diagnostics to study the temporal evolution of 2D distributions of potential and turbulence, including the long-range potential correlations with dual HIBP. Highlights in plasma potential profile evolution, a link between potential, density and confinement, geodesic acoustic modes, steady and chirping Alfvén eigenmodes, turbulent particle flux are presented.

2D poloidal contour plots of plasma potential, plasma density, and their fluctuations have been measured in low density plasmas sustained by Electron Cyclotron Resonance Heating using a heavy ion beam probe (HIBP) system in the TJ-II stellarator. A HIBP has been used in the new energy scanning mode to obtain the measurements for a 2D poloidal cross section of the stellarator. The 2D map for the absolute plasma potential shows a local maximum in the plasma core as expected in low density plasma scenarios. Fluctuations in the HIBP secondary ion current, as a proxy of plasma density fluctuations, appear both in positive and negative density gradient regions, with a normalized level of density fluctuations higher in the negative density gradient region. The TJ-II innovative experimental setup developed using a dual HIBP diagnostic paves the way for model validation on core plasma potential asymmetries and particle transport and fluctuations under positive and negative density gradient scenarios.

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 µA.

The aim of the report is to show the development of HIBP diagnostics on the TJ-II stellarator and, as a result, the expansion of the range of plasma parameters measurements. The first Heavy Ion Beam Probe (HIBP-1) diagnostic is being used on TJ-II stellarator since 2000. It has been shown significant progress in the measurements of plasma profiles and oscillations. The second HIBP-2 system was installed on TJ-II in 2012. Dual HIBP system, consisting of two identical HIBP-1 and HIBP-2 located 1/4 torus apart, provides the measurement of the long-range correlations of plasma parameters in the full plasma column. Low noise high gain (10(7) V/A) preamplifiers with 1 MHz bandwidth sampling is used. They allow to study broadband turbulence and quasi-coherent modes like geodesic acoustic modes, Alfven eigenmodes, suprathermal electron induced modes, etc. New capabilities of the dual HIBP diagnostic in plasma potential and density investigations were demonstrated on TJ-II stellarator in the measurements of the correlation between fluctuations in different poloidal and toroidal locations: on the same field line, on the same magnetic surface or on different magnetic surfaces at different points, separated toroidally and/or poloidally. PACS: 52.70.Nc

The improvement of the light atomic injector for beam emission spectroscopy (BES) diagnostic for Uragan-2M was held. The investigation was carried out with the energy of the sodium ion beam was 20 ... 25 keV, the ion current up to 2 mA, and the beam diameter of 15 ... 20 mm with 2 types of neutralizers. Neutralization of the beam was carried out on sodium vapor at an evaporator temperature of up to 300 degrees C. The neutralization efficiency is now near 60 ... 80 % for Na ion current 1.5 ... 2 mA and 20 ... 25 keV beam energy. PACS: 52.70.Nc

The main results obtained in the TJ-II stellarator in the last two years are reported. The most important topics investigated have been modelling and validation of impurity transport, validation of gyrokinetic simulations, turbulence characterisation, effect of magnetic configuration on transport, fuelling with pellet injection, fast particles and liquid metal plasma facing components. As regards impurity transport research, a number of working lines exploring several recently discovered effects have been developed: the effect of tangential drifts on stellarator neoclassical transport, the impurity flux driven by electric fields tangent to magnetic surfaces and attempts of experimental validation with Doppler reflectometry of the variation of the radial electric field on the flux surface. Concerning gyrokinetic simulations, two validation activities have been performed, the comparison with measurements of zonal flow relaxation in pellet-induced fast transients and the comparison with experimental poloidal variation of fluctuations amplitude. The impact of radial electric fields on turbulence spreading in the edge and scrape-off layer has been also experimentally characterized using a 2D Langmuir probe array. Another remarkable piece of work has been the investigation of the radial propagation of small temperature perturbations using transfer entropy. Research on the physics and modelling of plasma core fuelling with pellet and tracer-encapsulated solid-pellet injection has produced also relevant results. Neutral beam injection driven Alfvénic activity and its possible control by electron cyclotron current drive has been examined as well in TJ-II. Finally, recent results on alternative plasma facing components based on liquid metals are also presented.

Advanced heavy ion beam probe (HIBP) operates on the T-10 tokamak with 20-130 mu A Tl+ beam accelerated up to 330 keV. The HIBP has a unique capability to measure the mean value of the core plasma potential, and the oscillations in potential phi, density n(e) and poloidal magnetic field simultaneously in 5 spatially separated sample volumes for OH and ECRH plasmas with (n) over bar (e) = (0.3 - 5) x10(19) m(-3), 100 < I-pl < 330 kA. Time evolution of local plasma parameters and/or radial profiles can be measured in a single shot. The profile in the range 0.25 < rho < 1 is available shot by shot for B-0 < 2.2 T. The paper describes main elements of hardware: injector, beamlines, control systems, analyzer, power supplies, and software for HIBP. Physical examples show that HIBP can measure the cross-phase of density oscillations, the poloidal phase velocity of turbulence rotation, the poloidal electric field and the radial turbulent particle flux. Spectral analysis allows us to distinguish various types of turbulence, such as broadband (< 500 kHz), quasicoherent, tearing and geodesic acoustic modes.

Alfven eigenmodes were studied in the low magnetic shear flexible heliac TJ-II NBI-heated plasmas by heavy ion beam probe (HIBP), which is capable to measure simultaneously the oscillations of the plasma electric potential, density and poloidal magnetic field in the bulk plasmas. The L-mode hydrogen plasma was investigated at various magnetic configurations with rotational transform iota(a)/2 pi similar to 1.5-1.6. Co-, counter- and balanced beam injection were explored. The present study was focused on the high-frequency chirping modes with 250 kHz < f(AE) < 350 kHz at the low-density (n(e)) over bar = (0.5-0.7) x 10(19) m(-3) NBI-heated plasmas without auxiliary ECRH. Here we report the observation of the various types of chirping modes, differing by frequency, radial location, amplitude and shape of the frequency dependence on time (burst pattern). Remarkably, the same mode may evolve, changing its burst pattern in the same frequency range in the single discharge. The radial scan of the HIBP sample volume indicates the radial evolution of the potential and density perturbation during the single frequency burst of the chirping mode. The individual burst of the chirping-up mode can propagate outward with volume-averaged radial velocity approximate to 70 m s(1). The frequency raise during the burst is in line with Alfven frequency dependence on density, which decreases over the propagation area.

Electric field. or electric potential phi plays a key role in the transport and turbulence of toroidal plasmas. It is believed that mean radial E-r suppresses the turbulence eddies via E x B shear, while oscillatory E-r (zonal flows and geodesic acoustic modes, GAM) presents the mechanism of the turbulence self-regulation. Various aspects of the electron cyclotron resonance heating (ECRH), e.g. variation of power PECRH value and deposition effect on the static and oscillatory components of potential were studied in two machines of similar size by heavy ion beam probe (HIBP), operating now on the T-10 tokamak and TJ-II stellarator. HIBP measures in a wide density range (n) over bar (e) = (0.3-5) x 10(19) m(-3) and in various magnetic configurations in Ohmic and ECRH plasmas on T-10, and in ECRH and NBI-heated plasmas on TJ-II. With ECRH, the potential evolves towards the positive direction. This extra potential Delta phi increases with PECRH increase, while Delta phi decreases with plasma density raise. ECRH excites the broadband electrostatic oscillations in low-density TJ-II plasma, while in high-density T-10 plasma, this effect is opposite. In T-10 GAM frequency f(GAM) increases with P-ECRH in accordance with theoretical dependence on electron temperature (f(GAM) similar to T-e(1/2)), and GAM amplitude increases with P-ECRH. ECRH affects to NBI-excited Alfven eigenmodes (AEs): the steady frequency AEs transform to the chirping modes. In the low-density TJ-II plasmas, strong ECRH produces suprathermal (ST) electrons, exciting the electrostatic ST-modes. Dual HIBP measures the stable long-range potential correlations in TJ-II, resembling spatially localized low-frequency zonal flows in the core of ECRH plasmas. Finally, various aspects of the ECRH effects on the mean potential, broadband electrostatic turbulence, and on quasicoherent modes, including GAMs, AEs and ST-modes, are summarized.

This work is dedicated to simultaneous measurements of plasma potential oscillations at GAM frequencies in different locations on the T-10 tokamak and studying their correlation properties. Recent experiments with Heavy Ion Beam Probing and Langmuir probes have shown high coherency between signals of two diagnostics (up to 0.8) despite a large distance between the observation points: half of torus in toroidal and about pi in poloidal direction, up to 12 cm in radial direction. The phase shift between potentials measured with two diagnostics has been obtained in two plasma scenarios. It was found the most likely that potential oscillations at the GAM frequency propagate outward, but influence of 2 pi phase shift cannot be excluded.

Recent experiments in low magnetic shear flexible heliac TJ-II have shown that steady frequency and chirping Alfven Eigenmodes take place with 100 kHz< f(AE) <300 kHz at both pure NBI and combined ECR and NBI heated plasmas with low line-averaged density (n(e)) over bar = (0.3 ... 1.5)x10(19) m(-3) at Low Field Side (LFS) and High Field Side (HFS) of the plasma column. Furthermore, several types of low-frequency modes with f < 30 kHz, such as suprathermal electrostatic modes, tearing-like modes, quasicoherent modes with long-range potential correlations, were also observed. Power spectra for electrostatic and electromagnetic oscillations for all types of modes are presented along with their spatial location detected by dual Heavy Ion Beam Probe (HIBP).

The main results obtained in the TJ-II stellarator in the last two years are reported. The most important topics investigated have been: modelling and validation of impurity transport, validation of gyrokinetic simulations, turbulence characterisation, effect of magnetic configuration on transport, fuelling with pellet injection, fast particles and liquid metal PFCs. It must be noted that work done on TJ-II is relevant for W7-X.

1a IPFN, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal. 1 Fusion National Laboratory, CIEMAT, 28040, Madrid, Spain 2 National Research Centre ‘Kurchatov Institute’, 123182, Moscow, Russia 3 Institute of Plasma Physics, NSC KIPT, 611108, Kharkov, Ukraine 4 National Research Nuclear University MEPhI, 115409, Moscow, Russia 5 Moscow State University, 119991, Moscow, Russia 6 Moscow Institute of Physics and Technology, 141700, Dolgoprudny, Russia

Zonal flows and their high-frequency counterpart, the geodesic acoustic modes (GAMs) are considered as a possible mechanism of the plasma turbulence self-regulation. In the T-10 tokamak, GAM and broadband (< 200 kHz) turbulence of plasma potential and density have been directly studied by heavy ion beam probing from the plasma core to the edge. Regimes with Ohmic and auxiliary electron cyclotron resonance heating (ECRH) were studied (B-t = 1.7 - 2.4 T, I-p = 140 - 250 kA, <(n)over bar>(e) = (0.6 - 3) x 10(19) m(-3), P-EC <= 1.2 MW) for the plasma with tungsten rail limiter. GAMs are more pronounced during ECRH, when the typical frequencies f(GA)(M) were in the band 22 - 27 kHz for the main frequency peak and 25 - 30 kHz for the higher frequency satellite. Both GAM and satellite have uniform structure with constant frequencies over a wide radial extension, exhibiting the features of plasma eigenmodes. The main GAM peak has wider outer bound at the plasma edge than satellite. f(GAM) follows the theoretical expectation f(GAM) similar to root T/m(i)/R (for electron temperature at r/a = 0.7) for both OH and ECRH regimes in the wide temperature area, covering the whole operational limit of T-10. At the plasma periphery, the quasicoherent electrostatic mode with frequency 50 - 120 kHz coexists with GAM and satellite. (C) 2018 The Japan Society of Plasma Science and Nuclear Fusion Research

In the T-10 tokamak, the local fluctuations of poloidal electric field (E) over tilde (pol) and density (n) over tilde (e) were simultaneously measured by heavy ion beam probe (HIBP) with 5-slit energy analyzer that allow us to estimate the turbulent particle flux and E x B rotation velocity in the gradient zone of plasma column (r/a = 0.8). It was shown that at the Ohmic heating (OH) stage of discharge, the outward flux is in the range of 2 x 10(19) m(-2) s(-1), increasing at the ECRH stage by a factor of 1.5. At OH stage, the poloidal rotation velocity is about 4.5 km/s. (C) 2018 The Japan Society of Plasma Science and Nuclear Fusion Research

E. Sánchez, J. A. Alonso, I. Calvo, J. L. Velasco, T. Estrada, K. J. McCarthy, P. Monreal, L. G. Eliseev, A. V. Melnikov, A. Chmyga, L. I. Krupnik, A. I. Zhezhera, F. I. Parra, R. Kleiber and the TJ-II team Laboratorio Nacional de Fusión, CIEMAT, 28040, Madrid, Spain National Research Center, Kurchatov Institute, 123182, Moscow, Russia Institute of Plasma Physics, NSC KIPT, 310108, Kharkov, Ukraine Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford, OX1 3NP, UK Max-Planck Insitut für Plasmaphysik, Greifswald, 17491, Germany