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Feb 2013

Volume 84, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 84, 021101 (2013); http://dx.doi.org/10.1063/1.4789314 (14 pages)

Alexey Goncharov

Typical permanent magnet electrostatic plasma lens, characteristically about 15 cm long and 10 cm inner diameter. The magnets are shown in black between grey spacers. A set of cylindrical ring electrodes are located within the magnetic field region, with field lines connecting ring electrode pairs symmetrically about the lens midplane.

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back to top Nuclear Physics, Fusion and Plasmas

Single exposure three-dimensional imaging of dusty plasma clusters

Peter Hartmann, István Donkó, and Zoltán Donkó

Rev. Sci. Instrum. 84, 023501 (2013); http://dx.doi.org/10.1063/1.4789770 (5 pages)

Online Publication Date: 1 February 2013

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We have worked out the details of a single camera, single exposure method to perform three-dimensional imaging of a finite particle cluster. The procedure is based on the plenoptic imaging principle and utilizes a commercial Lytro light field still camera. We demonstrate the capabilities of our technique on a single layer particle cluster in a dusty plasma, where the camera is aligned and inclined at a small angle to the particle layer. The reconstruction of the third coordinate (depth) is found to be accurate and even shadowing particles can be identified.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Pure ion current collection in ion sensitive probe measurement with a metal mesh guard electrode for evaluation of ion temperature in magnetized plasma

Tung-Yuan Hsieh, Eiichirou Kawamori, and Yasushi Nishida

Rev. Sci. Instrum. 84, 023502 (2013); http://dx.doi.org/10.1063/1.4790175 (4 pages) | Cited 1 time

Online Publication Date: 6 February 2013

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This paper presents a new design of ion sensitive probe (ISP) that enables collection of pure ion current for accurate measurement of the perpendicular ion temperature in magnetized plasmas. The new type of ISP resolves a longstanding issue widely observed in ISP type measurements, namely, that the current-voltage characteristic is smeared by an unexpected electron current in the standard ISP model. The new ISP is equipped with a fine scale metal mesh on the sensor entrance to prevent electrons from flowing to the sensor, a phenomenon considered to be caused by the space-charge effect. The new ISP successfully measured the ion temperature of electron cyclotron resonance plasmas.
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52.70.Ds Electric and magnetic measurements
07.20.Dt Thermometers

Core-ion temperature measurement of the ADITYA tokamak using passive charge exchange neutral particle energy analyzer

Santosh P. Pandya, Kumar Ajay, Priyanka Mishra, Rajani D. Dhingra, and J. Govindarajan

Rev. Sci. Instrum. 84, 023503 (2013); http://dx.doi.org/10.1063/1.4791998 (9 pages)

Online Publication Date: 20 February 2013

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Core-ion temperature measurements have been carried out by the energy analysis of passive charge exchange (CX) neutrals escaping out of the ADITYA tokamak plasma (minor radius, a = 25 cm and major radius, R = 75 cm) using a 45° parallel plate electrostatic energy analyzer. The neutral particle analyzer (NPA) uses a gas cell configuration for re-ionizing the CX-neutrals and channel electron multipliers (CEMs) as detectors. Energy calibration of the NPA has been carried out using ion-source and ΔE/E of high-energy channel has been found to be ∼10%. Low signal to noise ratio (SNR) due to VUV reflections on the CEMs was identified during the operation of the NPA with ADITYA plasma discharges. This problem was rectified by upgrading the system by incorporating the additional components and arrangements to suppress VUV radiations and improve its VUV rejection capabilities. The noise rejection capability of the NPA was experimentally confirmed using a standard UV-source and also during the plasma discharges to get an adequate SNR (>30) at the energy channels. Core-ion temperature Ti(0) during flattop of the plasma current has been measured to be up to 150 eV during ohmically heated plasma discharges which is nearly 40% of the average core-electron temperature (typically Te(0) ∼ 400 eV). The present paper describes the principle of tokamak ion temperature measurement, NPA's design, development, and calibration along with the modifications carried out for minimizing the interference of plasma radiations in the CX-spectrum. Performance of the NPA during plasma discharges and experimental results on the measurement of ion-temperature have also been reported here.
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52.70.-m Plasma diagnostic techniques and instrumentation
52.25.Ya Neutrals in plasmas
52.55.Fa Tokamaks, spherical tokamaks
07.20.Ka High-temperature instrumentation; pyrometers
07.20.Dt Thermometers

Identification and control of plasma vertical position using neural network in Damavand tokamak

H. Rasouli, C. Rasouli, and A. Koohi

Rev. Sci. Instrum. 84, 023504 (2013); http://dx.doi.org/10.1063/1.4791925 (12 pages)

Online Publication Date: 21 February 2013

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In this work, a nonlinear model is introduced to determine the vertical position of the plasma column in Damavand tokamak. Using this model as a simulator, a nonlinear neural network controller has been designed. In the first stage, the electronic drive and sensory circuits of Damavand tokamak are modified. These circuits can control the vertical position of the plasma column inside the vacuum vessel. Since the vertical position of plasma is an unstable parameter, a direct closed loop system identification algorithm is performed. In the second stage, a nonlinear model is identified for plasma vertical position, based on the multilayer perceptron (MLP) neural network (NN) structure. Estimation of simulator parameters has been performed by back-propagation error algorithm using Levenberg–Marquardt gradient descent optimization technique. The model is verified through simulation of the whole closed loop system using both simulator and actual plant in similar conditions. As the final stage, a MLP neural network controller is designed for simulator model. In the last step, online training is performed to tune the controller parameters. Simulation results justify using of the NN controller for the actual plant.
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52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation
07.05.Dz Control systems
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

2D divertor heat flux distribution using a 3D heat conduction solver in National Spherical Torus Experiment

K. F. Gan, J-W. Ahn, J.-W. Park, R. Maingi, A. G. McLean, T. K. Gray, X. Gong, and X. D. Zhang

Rev. Sci. Instrum. 84, 023505 (2013); http://dx.doi.org/10.1063/1.4792595 (8 pages)

Online Publication Date: 21 February 2013

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The divertor heat flux footprint in tokamaks is often observed to be non-axisymmetric due to intrinsic error fields, applied 3D magnetic fields or during transients such as edge localized modes. Typically, only 1D radial heat flux profiles are analyzed; however, analysis of the full 2D divertor measurements provides opportunities to study the asymmetric nature of the deposited heat flux. To accomplish this an improved 3D Fourier analysis method has been successfully applied in a heat conduction solver (TACO) to determine the 2D heat flux distribution at the lower divertor surface in the National Spherical Torus Experiment (NSTX) tokamak. This advance enables study of helical heat deposition onto the divertor. In order to account for heat transmission through poorly adhered surface layers on the divertor plate, a heat transmission coefficient, defined as the surface layer thermal conductivity divided by the thickness of the layer, was introduced to the solution of heat conduction equation. This coefficient is denoted as α and a range of values were tested in the model to ensure a reliable heat flux calculation until a specific value of α led to the constant total deposited energy in the numerical solution after the end of discharge. A comparison between 1D heat flux profiles from TACO and from a 2D heat flux calculation code, THEODOR, shows good agreement. Advantages of 2D heat flux distribution over the conventional 1D heat flux profile are also discussed, and examples of 2D data analysis in the study of striated heat deposition pattern as well as the toroidal degree of asymmetry of peak heat flux and heat flux width are demonstrated.
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28.52.Fa Materials
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation
02.30.Nw Fourier analysis

Performance of an inverted ion source

M. C. Salvadori, F. S. Teixeira, L. G. Sgubin, W. W. R. Araujo, R. E. Spirin, E. M. Oks, and I. G. Brown

Rev. Sci. Instrum. 84, 023506 (2013); http://dx.doi.org/10.1063/1.4793377 (5 pages)

Online Publication Date: 27 February 2013

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Whereas energetic ion beams are conventionally produced by extracting ions (say, positive ions) from a plasma that is held at high (positive) potential, with ion energy determined by the potential drop through which the ions fall in the beam formation electrode system, in the device described here the plasma and its electronics are held at ground potential and the ion beam is formed and injected energetically into a space maintained at high (negative) potential. We refer to this configuration as an “inverted ion source.” This approach allows considerable savings both technologically and economically, rendering feasible some ion beam applications, in particular small-scale ion implantation, that might otherwise not be possible for many researchers and laboratories. We have developed a device of this kind utilizing a metal vapor vacuum arc plasma source, and explored its operation and beam characteristics over a range of parameter variation. The downstream beam current has been measured as a function of extraction voltage (5–35 kV), arc current (50–230 A), metal ion species (Ti, Nb, Au), and extractor grid spacing and beamlet aperture size (3, 4, and 5 mm). The downstream ion beam current as measured by a magnetically-suppressed Faraday cup was up to as high as 600 mA, and with parametric variation quite similar to that found for the more conventional metal vapor vacuum arc ion source.
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52.50.Dg Plasma sources
29.25.Ni Ion sources: positive and negative

Development of a polarization resolved spectroscopic diagnostic for measurements of the vector magnetic field in the Caltech coaxial magnetized plasma jet experiment

T. Shikama and P. M. Bellan

Rev. Sci. Instrum. 84, 023507 (2013); http://dx.doi.org/10.1063/1.4793403 (7 pages)

Online Publication Date: 28 February 2013

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In the Caltech coaxial magnetized plasma jet experiment, fundamental studies are carried out relevant to spheromak formation, astrophysical jet formation/propagation, solar coronal physics, and the general behavior of twisted magnetic flux tubes that intercept a boundary. In order to measure the spatial profile of the magnetic field vector for understanding the underlying physics governing the dynamical behavior, a non-perturbing visible emission spectroscopic method is implemented to observe the Zeeman splitting in emission spectra. We have designed and constructed a polarization-resolving optical system that can simultaneously detect the left- and right-circularly polarized emission. The system is applied to singly ionized nitrogen spectral lines. The magnetic field strength is measured with a precision of about ±13 mT. The radial profiles of the azimuthal and axial vector magnetic field components are resolved by using an inversion method.
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52.75.-d Plasma devices
07.55.Ge Magnetometers for magnetic field measurements
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