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  • Articles  (6)
  • American Institute of Physics (AIP)  (6)
  • International Union of Crystallography (IUCr)
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  • Articles  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4617-4617 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A nonintrusive method to measure low level stochastic electric fields in hot plasmas is being investigated in the TJ-I tokamak (R=30 cm, a=10 cm, Ip〈60 kA, BT〈1.5 T). It is based on the measurement of ion temperature of particles with different masses, i.e., protons and impurities, by the Doppler line width of their emission lines. It is hypothesized that its difference is due to gross mass motion produced by E˜×B. As a guide for data interpretation, we compare our results with typical values of fluctuating electric fields obtained by Langmuir probes at the plasma periphery. The ion temperatures of representative impurities like C V and O V, have been measured by the Doppler line width of near UV lines 2271 and 2781 A(ring), respectively. The proton temperature has been measured analyzing the Hβ and Hα line wings whose emission is due to highly energetic neutrals. Results of fluctuating electric fields obtained by this method as a function of radius and plasma density will be presented. The deduced fluctuating electric fields are higher at the plasma periphery than at the plasma center and in the latter much higher at low than at high densities. An approach to distinguish between radial and poloidal electric field fluctuations is being addressed by modeling experimental results with a simulation code.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A spectroscopic method to directly measure the nonthermal velocity fluctuations is being studied in the TJ-I tokamak. The method is based on converting velocity in intensity fluctuations by subtracting the signals received at two symmetric positions of a spectral emission line. This is accomplished by means of a multichannel detector in which the channels respond to the line intensity at different wavelengths and positions within a single spectral line. A multichannel plate photomultiplier, with an anode split in 8×8 parts, is optically coupled by means of an anamorphic optical system, to the focal plane of a 1 m spectrometer where the image of a spectral line is formed. Some individual anodes are grouped to configurate four acquisition channels which are fled into four current amplifiers. The 100 kHz bandwidth signals are stored in a digital oscilloscope connected to a VAX computer, where the signals are processed. A simple simulation allows us to relate the differential signal between symmetrical channels to velocity in cases where the radial extension of the emitting ion is comparable to the radial correlation length of the turbulence causing the velocity fluctuations. The influence of the detection statistics on the measurement is analyzed. Preliminary results obtained in the TJ-I tokamak, using this system, will be presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5196-5198 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A code for calculating the actual spectral line shapes in magnetically confined plasmas of the tokamak type is described. The code determines the resulting line shape averaged along the line-of-sight of the spectrometer, starting from prescribed thermal temperature, ion emissivity, and flow profiles, for a plasma immersed in a magnetic field. In addition, the influence on the impurity linewidths of nonthermal fluctuating velocities due to fluctuating electric fields and to possible magnetic fluctuations is also included. Typical applications of the code to spectral data analysis in the TJ-I tokamak are given.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 680-682 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We outline designs for several rare-earth-based phosphor powder detector systems for monitoring the broadband VUV plasma radiation in the TJ-II torsatron device. These include a global radiation detector, a detector with temporal and spectral resolution, and a third with radial scanning capabilities. We describe the selection of a phosphor powder for this application having good response from the soft x ray to the VUV, a fast response time, and the capability of operation at high temperatures. In addition, we give details of a method developed in-house for depositing thin uniform layers of powder on glass substrates for use as phosphor screens. Finally, we present some detector test results obtained in the plasma of the TJ-I U torsatron. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact and highly sensitive pinhole camera has been developed for acquiring broadband vacuum ultraviolet (VUV) emission profiles of plasmas in the TJ-II. Its principal purpose is to obtain profiles with sufficiently high resolution so as to aid in the search for topological structures in stellarator plasmas. It can also be used to support experiments such as impurity injection by laser ablation. The original and purpose-designed camera reported here provides optimum sensitivity over a broad spectral range. In the camera vacuum chamber, plasma radiation passes through a pinhole and a filter before impinging on a 5×30 mm area of a P-46 phosphor screen. Thin screens of this material were extensively characterized using calibrated monochromatic VUV sources and it was found that their response is maximized when operated in reflection mode.1 Luminescent light emitted from the vacuum side of the screen is then focused by a toroidal mirror (the pinhole is cut in its center) onto the outside of a quartz window which is mounted on the side of camera. Finally, this intermediate image is relayed onto the surface of a gated and intensified linear photodiode array (25 μm by 25 mm) having 700 active pixels. This system is capable of obtaining radial VUV profiles every 12 ms and of recording them in ≥100 ns. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article, we report on the hardware and software of an eight-channel, high-resolution, spectroscopic diagnostic system that has been built for the TJ-II flexible heliac. This system is currently being used on TJ-II to measure impurity ion temperature and poloidal rotation using passive emission spectroscopy. The principal features of the diagnostic include independent focusing of its channels, high sensitivity for performing Doppler measurements in low-density ECR-heated plasmas, as well as a flexible and fast in-house-developed software program for performing integrated data reduction and analysis. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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