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  • 1
    Electronic Resource
    Electronic Resource
    Upgrade of the RFX microwave frequency modulated reflectometer to ultrafast sweeping rate : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1056-1059 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The swept homodyne reflectometer installed on the RFX experiment is composed of five units which cover the frequency range 26.5–110 GHz. This diagnostic system is based on solid state IMPATT sources and can be operated in the O or X mode. During the first operation, at a sweep rate of 0.1 GHz/μs, the typical density fluctuations present in the reversed field pinch configuration usually prevented correct profile reconstruction, which was possible only in some special cases. To increase the sweep speed and overcome this limit, a new IMPATT driver has been built and IF amplifiers, control, and acquisition systems have been modified accordingly. The new configuration has been extensively tested in the 34–38 GHz range with a modulation rate exceeding 4 GHz/μs on many different plasma conditions. Measurements on plasma showed that both the phase and reflected power level can be correctly recovered from the IF signals. These results indicated the criteria necessary to extend the fast sweep capability to the full 26.5–110 GHz range. In this article we present how the fast sweep capability is now being extended to the whole reflectometric diagnostic and the first successful plasma measurements obtained using a test reflectometric system. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149320
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  • 2
    Electronic Resource
    Electronic Resource
    Improved performance of the Thomson scattering system in RFX (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1416-1420 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A Thomson scattering diagnostic is used in the RFX reversed field pinch experiment to measure single pulse, multipoint electron temperature (Te) profiles. Recent significant improvements have provided reliable and routine operation of the diagnostic. Custom developed CAMAC charge analog-to-digital converters have been introduced, which sample the plasma light 170 ns after the laser light and have greater sensitivity. The spectrometer configuration and the calibration procedure have been optimized. These upgrades have finally led to better fitted scattering spectra and more regular estimates of Te profiles, allowing the measurement of temperatures as low as 20 eV. The introduction of a second spectrometer has recently added a further ten positions to the original ten point profile, resolving the often steep Te edge gradient. On axis values are in good agreement with other Te measurements from SXR diagnostics (either SiLi and double filter method). Te profiles are typically rather flat, but some dependence on the plasma parameters, like density and pinch parameter, has been drawn. Significant Te profile modifications have been observed during transient events like pulsed poloidal current drive and pellet injection. The diagnostic will be completed soon, allowing production of 27 point profiles, with the introduction of the third spectrometer. Double pulse operation of the laser is in progress.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149629
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  • 3
    Electronic Resource
    Electronic Resource
    The time-of-flight neutral particle analyzer and its calibration system for the RFX experiment : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 330-332 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple and low cost time-of-flight neutral particle analyzer has been operated on the RFX experiment. Simplifications have been introduced with respect to already existing similar devices, obtaining a low cost and reliable system. Good performance has been reached for hydrogen plasmas producing charge exchange H neutrals whose energy is lower than 3000 eV. Moreover a simple ion beam system has been projected and built to calibrate the electron multipliers used on the time-of-flight analyzer. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146403
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  • 4
    Electronic Resource
    Electronic Resource
    First results in reflectometric plasma density measurements on RFX : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 406-408 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A five-band, high-sweep-speed reflectometer system for the RFX reverse field pinch experiment has been developed. To control the high-noise environment we improved the intermediate frequency amplifying and conditioning system. We checked the modified system using a new in situ calibration method that pointed out the improvements. This new method is a suitable one for calibrating the reflectometer, because it allows one to place a mirror in a well-defined position, thus giving a good radial (〈2 mm) and angular resolution (〈10−3 rad). Preliminary results on maximum density time evolution are presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146361
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  • 5
    Electronic Resource
    Electronic Resource
    Simple analytical model of gain saturation in microchannel plate devices (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 247-258 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We derive, discuss, and test against experimental data an analytical model of the gain saturation in microchannel plate (MCP) devices. By introducing a simple recharging circuit for each dynode, we extend the well-known, unsaturated gain model of Eberhardt to a microchannel operating in condition of gain saturation and show that the amplification of a current pulse and the voltage drop along the channel can be described by a pair of coupled differential equations. Solutions of these equations are given in various conditions, including an approximate solution, valid in the case of weak saturation and a general solution in implicit form. The behavior of a microchannel operating in current mode is studied by finding the transient and steady-state solutions obtained with an input step current wave form. Exact solutions are given for the charge gain of pulses with a short duration, compared to the dynode recharging time, and for the gain recovery of a microchannel after the amplification of a short pulse. The single channel saturation model is then extended to multistage MCP assemblies by taking into account the statistical distribution of the photoelectrons at the input and the spread of the multiplied electron cloud in the interplate gaps. The expressions found in this way are used for the best fit of experimental data from a Z-stack MCP photomultiplier operated in single and double pulse mode. Satisfactory agreement between the model and experimental data is obtained in the case of single pulse measurements, finding a reduced chi squared χ2=4.67. Less satisfactory agreement is found for double pulse data, giving χ2=7.46 and a clear indication that the model may be significantly improved by taking into account the charge redistribution among the dynodes during the recharging process, neglected in the present formulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144791
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  • 6
    Electronic Resource
    Electronic Resource
    Thomson scattering measurements in the RFX reversed field pinch : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 718-720 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The first systematic measurements of the electron temperature (Te) spatial profile have been obtained in the reversed field pinch experiment RFX with a single pulse Thomson scattering (TS) diagnostic. Scattered light from a ruby laser pulse (E≤15 J, Δt=30 ns) is collected through three objectives from 10 positions along a diameter in the plasma equatorial plane, with a spatial resolution of 2.5 cm. Plasma discharges with current in the range 700–900 kA have been investigated finding evidence of a quite flat Te profile. Data dispersion significantly greater than experimental uncertainties provides an indication of remarkable plasma fluctuations. Results are in good agreement with Te measurements from other single chord spectroscopic diagnostics (SiLi detector and SXR double filter), showing a reliable operation down to an electron density ne=3×1019 m−3. Integration of this apparatus with a ND:YLF laser system for multipulse Thomson scattering measurements, sharing the same input optics, is under way. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147762
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  • 7
    Electronic Resource
    Electronic Resource
    Development of a multipoint Thomson scattering system for a large reversed field pinch experiment : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2846-2848 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A multipoint Thomson scattering system is under development for the measurement of Te and ne spatial profiles in RFX, a large (a=0.48 m, R=2 m, I≤2 MA) reversed field pinch experiment. In this system, the beam from a low divergence ruby laser (E=15 J, Δt=30 ns) is focused to cross the plasma in the equatorial plane. The scattering signal from 30 locations along a plasma diameter is collected by means of high transmission fiber optic bundles. An effective viewing dump was obtained by engraving sharp poloidal grooves in the first wall graphite tiles. The scattering light spectra are analyzed by means of three spectrometers, each including an F/3.4, aberration corrected, holographic grating and a 40-mm-diam MCP photomultiplier with a 10×10 anode array. These detectors use a high strip current, V-plate, electron multiplier with 105 electron gain and have a recovery time of less than 30 μs. In the 300-channel data acquisition electronics, the plasma light background may be sampled 100 ns before the scattering pulse. The system is designed in order to achieve a spatial resolution of 2.5 cm, useful to study small-scale correlation phenomena, and will also measure fast, submillisecond fluctuations of Te and ne by exploiting the two-pulse capability of the laser.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141802
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  • 8
    Electronic Resource
    Electronic Resource
    Electronics for microchannel plate detectors of a Thomson scattering system : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4944-4946 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe electronics developed for the operation of multianode microchannel plate (MCP) photomultipliers in a multipoint Thomson scattering system. A pulsed, digitally programmable high voltage power supply with current feedback and a built-in protection circuit has been designed to bias the detector in safe conditions, taking into account the nonlinear behavior of the MCP resistance. The 180-V photocathode voltage is switched by a fast, current driven, optically coupled metal-oxide-semiconductor field-effect transistor. Gating pulses with 10-ns rise time and 50–500-ns programmable duration are generated with negligible noise at the output anodes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143505
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  • 9
    Electronic Resource
    Electronic Resource
    The kinetics of cellulose fiber degradation and correlation with some tensile properties (1994)
    Weinheim : Wiley-Blackwell
    Acta Polymerica 45 (1994), S. 47-49 
    Details
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cellulosic degradation of cotton and flax yarns caused by light, heat and heterogeneous acid-catalyzed hydrolysis was studied. These processes were followed by measuring changes in intrinsic fluidity (1/DPw): two principal stages, characterized by different zero-order kinetics, take place. A relation between changes in intrinsic fluidity with some mechanical properties of the same yarns during the degradation process was found.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/actp.1994.010450109
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  • 10
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    Simple analytical model of gain saturation in microchannel plate devices (1994)
    American Institute of Physics
    Details
    Publication Date: 1994-01-01
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics
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