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Nov 2001

Volume 72, Issue 11, pp. 4025-4314

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back to top NUCLEAR PHYSICS, FUSION and PLASMAS

Reducing influence of ion current on measurements of electron energy distributions in collisional plasmas

V. I. Demidov, S. V. Ratynskaia, and K. Rypdal

Rev. Sci. Instrum. 72, 4106 (2001); http://dx.doi.org/10.1063/1.1408933 (4 pages) | Cited 4 times

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A method for reducing the influence of ion current on probe measurements of electron velocity distributions in plasmas has been developed and tested in noble gas afterglow plasmas. It is valid for diffusive transport of ions to the probe. Experiments have demonstrated high accuracy of the proposed method. © 2001 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.80.Hc Glow; corona
52.25.Fi Transport properties

Fiber optic catalytic probe for weakly ionized oxygen plasma characterization

D. Babič, I. Poberaj, and M. Mozetič

Rev. Sci. Instrum. 72, 4110 (2001); http://dx.doi.org/10.1063/1.1409567 (5 pages) | Cited 32 times

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Construction and operation of a novel fiber optic catalytic probe is presented. The probe is intended for measurements of atomic oxygen density in plasma postglows. The operation of the probe is based on a catalytic recombination of oxygen atoms and remote temperature sensing via optical fiber. Compared to the classical catalytic probes, the new approach results in smaller dimensions, better sensitivity, and higher immunity to the electromagnetic interference. Comparative measurements of atomic oxygen density performed simultaneously with both types of probes demonstrated a superior performance of the novel probes. © 2001 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
07.60.Vg Fiber-optic instruments
42.81.Pa Sensors, gyros
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Measurement of spurious impurity concentrations in ASDEX Upgrade by x-ray spectroscopy

D. Bolshukhin, R. Neu, D. Schlögl, and R. Dux

Rev. Sci. Instrum. 72, 4115 (2001); http://dx.doi.org/10.1063/1.1405792 (10 pages) | Cited 1 time

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A two channel multicrystal spectrometer of Bragg geometry was constructed for measurements of absolute photon fluxes of ASDEX Upgrade plasmas in the wavelength range from 0.5 up to 26 Å. The calibration of the spectrometer was done by an ab initio calculation using the absolute reflection data from literature of four crystals. The calibration was validated by the direct comparison with other absolute calibrated diagnostics at the ASDEX Upgrade as well as by using the impurity transport code STRAHL. The absolute impurity concentrations of elements from N up to Cu have been extracted. O and F appear to be main impurity components after C, which is routinely measured by an independent diagnostic. Despite the significantly lower concentration of Ar, it contributes measurably to Zeff and can account for main plasma impurities as well. Other impurities either have never been seen or appear only sporadically (like Fe and Cu) and normally do not contribute significantly to the plasma radiation in the soft x-ray range. © 2001 American Institute of Physics.
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52.70.La X-ray and γ-ray measurements
52.55.Fa Tokamaks, spherical tokamaks
07.85.Nc X-ray and γ-ray spectrometers
52.25.Vy Impurities in plasmas

Electronics and signal processing for the multichord far-infrared polarimeter of the RFX experiment

E. Zilli, F. Milani, M. O’Gorman, L. Giudicotti, and S. L. Prunty

Rev. Sci. Instrum. 72, 4125 (2001); http://dx.doi.org/10.1063/1.1412262 (14 pages) | Cited 1 time

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This article describes the realization and testing of the electronic system which forms part of the multichannel far-infrared (FIR) polarimeter for the RFX machine, a plasma confinement experiment with Reversed Field Pinch (RFP) configuration. The electronic system, which comprises the detectors, the signal-processing electronics, and the motion electronics for the half-wave plate movement, is described. Emphasis is placed in the analysis of the polarimeter signals, which permits an in-depth understanding of the performance of the data processing electronics and the role of the various sources of noise in the system. After a brief outline of the basic principle of the measurement, the choice of detectors and their characteristics are described in order to achieve the best performances at the FIR wavelength (λ = 118.8 μm) of interest. Various tests, which are described, confirmed the need for a specifically designed pyroelectric detector capable of operating in the hostile magnetic environment near the machine. The processing of the raw polarimeter signals to produce the required sum and difference signals and to convert them into dc signals with 3 ms time constant is presented. These signals are synchronous with a chopper signal on the FIR beam and are subsequently fed to a lock-in amplifier. An accurate analysis of the data processing procedure is described, which helps to clarify the understanding of the output signals that are eventually recorded in the data acquisition system. In particular, various sources of noise, such as thermal noise of the detectors, laser fluctuations, spurious signals at harmonics of the chopper frequency, and phase jitter of the chopper, are evaluated, discussed, and compared with the observed signals. Finally, the control circuitry for the movement of the half-wave plates, both for manual control and for the programmed sequences of zero-search and calibration performed by a PLC control system, is described. Calibration curves obtained during experiments are also reported. © 2001 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.58.Lq Z-pinches, plasma focus, and other pinch devices
07.60.Fs Polarimeters and ellipsometers
07.68.+m Photography, photographic instruments; xerography
07.05.Hd Data acquisition: hardware and software

Analytical simulation of microwave reflectometry of a plasma cylinder

L. G. Bruskin and A. Mase

Rev. Sci. Instrum. 72, 4139 (2001); http://dx.doi.org/10.1063/1.1409570 (6 pages)

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An analytical solution of a time-dependent two-dimensional (2D) full-wave equation is obtained for the case of microwave propagation in a plasma with axial symmetry. The 2D structure of the electromagnetic wave in a nonmagnetized plasma (or an ordinary wave in a magnetized plasma) is studied for the general case of arbitrary time dependence of the incident wave emitted by the horn. The solutions cover the cases of conventional microwave reflectometry as well as the ultrashort pulse reflectometry of fusion and processing plasma. Analytical expressions can be further applied to study plasma density fluctuations as well as effects of plasma curvature and multidimensionality. The 2D plasma cylinder model is deemed by the authors to be more realistic as compared to the one-dimensional plasma slab model previously employed in all the analytical and most numerical treatments since the plasma in the fusion toroidal devices, mirror machines, and plasma processing chambers can be considered axially symmetric on the scale relevant to microwave reflectometry. © 2001 American Institute of Physics.
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52.70.Gw Radio-frequency and microwave measurements
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.65.-y Plasma simulation
52.25.Gj Fluctuation and chaos phenomena
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