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Heavy ion beam probe (HIBP) is a unique tool for studying the electric potential and various turbulence characteristics both in the core and at the edge of toroidal plasmas. The position of the HIBP measurement point in the plasma is determined by the probe beam energy and its entrance angle into the plasma. The probe beam energy is constant during the plasma discharge and determines the maximum penetration depth of the beam into the plasma. The beam entrance angle into the plasma can vary during the discharge, and the set of positions of HIBP measurement points for different beam entrance angles creates a so-called detector line. The set of detector lines for different probe beam energies represents a 2D region (detector array) in the vertical cross section of the plasma. The article presents a method for constructing 2D distributions of plasma parameters over the detector array on the T-10 tokamak by the example of the plasma electric potential. [ABSTRACT FROM AUTHOR]

Radial distributions of the electric potential and plasma density oscillations have been measured in the T-10 tokamak ohmic plasma. Radial distributions of the amplitude and frequency of the geodesic acoustic mode are plotted according to the data on the fluctuations of the electric potential of the plasma, and radial distributions of the amplitude and frequency of the quasi-coherent mode are plotted according to the data on the fluctuations of the plasma density. The quasi-coherent mode corresponds to the major part of the turbulent particle flow, the geodesic acoustic mode as a high-frequency branch of zonal flows is involved in the turbulence regulation, which makes these objects very important for plasma physics. The paper presents the results obtained in different operating modes of the T-10 tokamak. [ABSTRACT FROM AUTHOR]

For low-frequency kHz) plasma electric potential oscillations, measured in two toroidally spaced vertical cross sections of the TJ-II stellarator ( m, m, T) using double heavy ion beam probe diagnostics, long-range correlations are observed, as well as their toroidal and poloidal symmetry . It is shown that long-range correlations do not have a magnetic or density component. Thus, the low-frequency symmetric structures of the electric potential found in the hot plasma area are zonal flows. Their quantitative characteristic is the square coherence coefficient . A two-dimensional map of zonal flows (long-range correlations) in the low-density m–3 regime with ECR heating has been plotted for the first time and their ballooning structure (dominance on the low field side of the vessel) has been found. The decrease in the level of electrostatic turbulence ( kHz) observed in this region is consistent with the theoretically predicted suppression of broadband turbulence due to zonal flows. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

New experimental observations of the plasma potential using the heavy ion beam probe diagnostic are presented together with a theoretical description of the formation of the electric field Er in the T-10 circular tokamak (B0 = 1.5-2.5 T, R = 1.5m, a = 0.3 m). Ohmically heated (OH) deuterium plasmas with main plasma parameters ne = (0.6-4.7) × 1019 m-3, Te(0) < 1.3 keV, Ti(0) < 0.6 keV are characterized by a negative potential φ(ρ) with maximum negative values of φ(6 cm) = -1400V with respect to the wall. The potential profile monotonically increases towards the plasma edge. A density rise due to gas puff is accompanied by a plasma potential that becomes increasingly negative. When the density approaches values in the range ne = (2.5-3.5) × 1019 m-3, the value of the plasma potential saturates, while the energy confinement time still increases up to a saturation value that is obtained at a slightly higher density. With auxiliary heating by electron cyclotron resonance heating (ECRH) up to 1.2MW, Te(0) increases (up to 3 keV) and the absolute value of the plasma potential decreases. In some cases the plasma potential changes its sign and becomes positive at the edge. The radial profile of Er and its dependence on ne and Ti are qualitatively explained by a neoclassical model in the core, and a turbulent dynamic model (Braginskij magnetohydrodynamic equations) in the edge. [ABSTRACT FROM AUTHOR]

Alfvén eigenmodes (AEs) were studied in neutral beam injection (NBI) heated plasmas in the TJ-II stellarator using a heavy ion beam probe (HIBP) in the core, and by Langmuir (LP) and Mirnov probes (MP) at the edge. AEs were detected over the whole plasma radius by the HIBP with a spatial resolution of about 1 cm. AE-induced oscillations were detected in the plasma density ne, electric potential φ and poloidal magnetic field Bpol with frequencies 50 kHz < fAE < 300 kHz. The LP, MP and HIBP data showed a high level of coherency for specific branches of AEs. Poloidal mode wave-vectors kθ, mode numbers m (m < 8) and propagation velocities Vθ ~ 30 km s-1 were detected for various branches of AEs, having different radial locations. When the density rose due to NBI fuelling, the AE frequency decreased as predicted by the Alfvén law fAE ~ ne-1/2, During the AE frequency decay the following new AE features were observed: (i) the poloidal wave-vector kθ and mode number m remained constant, (ii) the cross-phases between the oscillations in Bpol, ne and electric potential remained constant, having an individual value for each AE branch, (iii) Vθ decreased proportional to the AE frequency. The interaction of the AEs with the bulk (thermal) plasma resulted in clearly pronounced quasi-coherent peaks in the electrostatic turbulent particle flux spectra. Various AE branches exhibited different contributions to the particle flux: outward, inward and also zero, depending on the phase relations between the oscillations in Epol and ne, which are specific for each branch. A comparison with MHD mode modelling indicated that some of the more prominent frequency branches can be identified as radially extended helical AEs. [ABSTRACT FROM AUTHOR]

Proposes the heavy ion-beam probing (HIBP) project for the mega ampere spherical tokamak to establish systematic research of the radial electric field as an idea to investigate both the reactor-related physics and basic plasma physics. HIBP optimization; Types of probing trajectories; Crossover of the secondaries; Optimal detector grid.

Discusses the specific features of the application of heavy ion beam probe systems to tight aspect ratio tokamaks. Brief description of the observed tokamaks from the viewpoint of the probing beam pass; Optimization procedure; Three-dimensional case.

Develops a procedure of fast calibration of the heavy ion beam probe parallel plate analyzer using the gas target and reference beam. Test facility in vitro calibration; Gas target in situ calibration; Nonideal effects in calibration.

Describes the application of the heavy ion beam probe (HIBP) diagnostics to the investigation of the plasma density and potential in the TJ-1 tokamak. Analyzer characteristics, calibration procedures and analysis of the plasma potential data; Plasma density.

This article presents long-focus ion beam injection systems developed for investigation of plasma parameters by heavy ion beam probing diagnostics in fusion devices. Ion beam parameters vary in a wide range of both beam intensity of alkali probing ions (1–100 μA) and initial energy (20–300 keV), determined by the experimental claims on each plasma device under study. This article describes the characteristics of beam extraction systems with transport ion optics and control, and accelerator power supplies with high stability (not worse than 10-5). Presented systems allow us a fine tuning of the beam focusing along the beam trajectory in plasmas studied. They provide an accurate spatial resolution of measurements in plasma of modern fusion devices up to 5 mm. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]