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  • 1
    Electronic Resource
    Electronic Resource
    Ionization balance in EBIT and tokamak plasmas : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1250-1255 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The equilibrium state in tokamak core plasmas has been studied using the relative intensities of resonance x-ray lines, for example Lyα (H-like), "w" (He-like), and "q" (Li-like) from test ions such as Ar+15, Ar+16, and Ar+17. A full spatial analysis involves comparison of the line intensities with ion diffusion calculations, including relevant atomic rates. A zero-dimensional model using a global ion loss rate approximation has also been demonstrated by comparison with the data collected from a Johann configuration spectrometer with a charged coupled device (CCD) detector. Since the lines are nearly monoenergetic, their intensities are independent of the instrument sensitivity and are directly proportional to the ion abundances. This method has recently been applied to Ar in the Oxford electron beam ion trap (EBIT) with a beam energy in the range 3–10 keV. Taking into account the cross sections for monoenergetic electron collisions and polarization effects, model calculations agree with the observed line ratios at 4.1 keV beam energy. This work will be expanded to provide nomograms of ionization state versus line intensity ratios as a function of EBIT beam energy. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1324755
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  • 2
    Electronic Resource
    Electronic Resource
    Quantitative spectroscopy of x-ray lines and continua in tokamaks (abstract) : 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. 1063-1063 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Crystal and synthetic multilayer diffractors, deployed either as flat Bragg reflectors, or curved, as in the Johann configuration, have been used to study the spectrum of COMPASS-D and other tokamaks in the wavelength region 1–100 Å. In particular, line emission from CIXVI and other He-like ions of the third atomic period elements have been shown to be a rich source of diagnostic information on ion transport and impurity ion accumulation, ion and electron temperatures, and plasma fluid velocities. In this article, we concentrate on the measurement of absolute photon fluxes and the derivation of volume emissivities of the lines and continua in the x-ray region. The sensitivities of these instruments to absolute photon flux are constructed from the individual component efficiencies, including published values of the diffractor reflectivities. Where diffractors have been used for which there is no published information, the reflectivity is measured using a double-axis goniometer or from line branching ratios. Changes in the effective ion charge state, Zeff, have been derived for different operating conditions, from the absolute intensity of the continuum at ∼4 Å in COMPASS-D. From the irradiances of the line emission, changes in the absolute level of impurities following "boronization" of the vacuum vessel have been documented.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147916
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  • 3
    Electronic Resource
    Electronic Resource
    Diagnostic characterization of a prepulsed carbon fiber Z pinch using spectral line intensity analyses (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1425-1429 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Plasma formation and x-ray generation efficiency of a carbon fiber Z pinch are dramatically improved by means of an optimized current prepulse. In this article results are presented of time-integrated and also time-resolved electron temperature measurements using the optical line emission of the coronal plasma surrounding a still, cold fiber. Two phases of discharges with current prepulse are studied: the preionization phase only in which time-integrated spectra of C II–C IV emission are recorded and time resolution of the heating phase after onset of the main current pulse using C III and C IV line emission. Experimentally obtained, n=3–4, 3–3, line ratios are fitted with collisional radiative, ADAS computations of line intensity ratios as a function of electron temperature, density, ne and variable confinement, τ. All levels up to n=5 are included with the influence of higher levels also accounted for. Deviations from coronal balance give an effective value for the product 〈neτ〉. As a result, the electron temperature of the preionized coronal plasma is estimated at Te=5 eV at a density of ne(approximate)1017 cm−3. The temperature rises to about 12 eV at the same density after the start of the main current with prepulse. Similar analytic techniques are applied to time-integrated C V and C VI XUV resonance lines from the main pinch and give plasma parameters in accord with the x-ray continuum diagnostics. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149630
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  • 4
    Electronic Resource
    Electronic Resource
    Vacuum ultraviolet, extreme ultraviolet, and x-ray line intensity normalization technique applied to tokamak plasmas : 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. 317-322 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An empirical procedure, "LINT," for relating emission line intensities of intrinsic impurity ions to their elemental contributions to the total, bolometric, radiation loss and the volume-averaged effective ion charge, Zeff, has been developed and applied to limiter plasmas in the JET tokamak. In this article we discuss extensions to the data base to include x-ray lines and continua intensities, applicable to a wider range of tokamak plasma configurations such as X-point plasmas and quasi-steady-state, edge-cooled ELMy H modes. Examples are shown of the technique applied to reference discharges during which the plasma configuration is changed continuously. The total data set, comprising line and continua irradiances, tomographic bolometry, and x-ray emission and Zeff imposes constraints on the diffusion parameters used in models of impurity ion transport. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149443
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  • 5
    Electronic Resource
    Electronic Resource
    Two-axis goniometer for reflectivity measurements of x-ray diffractors used in fusion research (abstract)a) : 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. 529-529 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Quantitative measurements of the line and continua emissivities and the analyses of spectral line profiles are essential steps in the interpretation of the x-ray emission from high-temperature fusion plasmas. One method of placing the emissivities on an absolute basis is to use an absolutely calibrated spectrometer to record the data. The overall sensitivity of the spectrometer can be constructed in terms of the efficiencies of its separate components, the most intractable being Rc, the reflection integral of the diffractor. To this end, a new, compact, two-axis diffractometer, incorporating modern robotic technology, such as direct-drive servomotors with closed-loop operation from built-in arcsec optical encoders, has been constructed. Improved features of this double-axis goniometer include the use of fixed line-of-sight x-ray sources with the capability of operation in the (1,−1) parallel, nondispersive mode or the antiparallel, (1,+1), dispersive mode. The diffractometer is now being used to calibrate x-ray diffractors, filters, mirrors, and detectors associated with x-ray spectroscopy of fusion plasmas. At certain wavelengths, where line branching ratios involving visible transitions are available, the fusion plasma may itself be used as a transfer standard of x-ray luminosity, allowing an independent check on the diffractometer values of Rc. Applications to the analyses of impurity concentrations in tokamaks are described while future applications of the diffractometer to radiation damage studies of x-ray and optical components [Hill et al., Rev. Sci. Instrum. 63, 5032 (1992)] used in D-T burning plasma experiments are envisaged. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146339
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  • 6
    Electronic Resource
    Electronic Resource
    High-frequency modulated light source for phase fluorometry and fluorescence lifetime imaging (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 48-51 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Phase fluorometry and fluorescence lifetime imaging require a source of exciting light which can be modulated at radiofrequency. This is difficult to achieve with reasonable efficiency using conventional light sources with external modulators such as Pockels cells, while laser sources are limited in wavelength tunability. In this paper a low-cost and versatile high-frequency modulated light source is described which is well suited to frequency-domain fluorescence measurements. The source is a modified deuterium arc lamp which can be driven directly at frequencies up to approximately 130 MHz, and which provides a highly stable source of ultraviolet and visible light. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146325
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  • 7
    Electronic Resource
    Electronic Resource
    Bragg rotor spectrometer for the JET tokamak (abstract) : 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. 5022-5022 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A Bragg rotor spectrometer uses diffractors ranging from LiF (420) (2d=0.18 nm) to a multilayer mirror (Ni–C 2d=11.7 nm). The extension to longer wavelengths is particularly useful at JET, where radiated power and Zeff are usually dominated by light impurities such as Be and C, whose H- and He-like transitions lie between about 2.5 and 10 nm. A hexagonal rotor scans six diffractors sequentially and gives either full coverage of the soft x-ray spectrum (to monitor a range of ionization stages of any possible impurity), or high monochromatic sensitivity (to monitor trace impurities and give time resolution of ∼10 μs for the study of transient events such as impurity injection). A large area gas proportional counter covers a Bragg angle range from 20° to 70°, with each of its ten anodes being connected to an independent amplifier-discriminator chain, allowing count rates up to 20 MHz to be processed. Moderate resolving power is provided by a 1:600 Soller collimator. A smaller rotor is mounted with a side-by-side array of four small diffractors, and is reciprocated over a relatively small Bragg angle range to give a time resolution of 20 ms for about ten representative lines (for routine analysis of radiated power components).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143479
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  • 8
    Electronic Resource
    Electronic Resource
    General purpose high-resolution x-ray crystal spectrometer (abstract) : 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. 5022-5022 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This spectrometer was designed to give access to a wide range of Bragg angles and crystal focal lengths while using the Rowland circle radius as a free parameter. Stability is achieved using a rigid beam or "Rowland chord,'' which provides a reference axis for all the critical alignments, the chord length being variable between about 0.2 and 5 m. Crystals of size up to 100×30×0.5 mm can be accommodated in a novel four-pillar jig, (λ/δλ) is typically 104 in the wavelength range from 0.1 to 1.3 nm, depending on the crystal. Various detectors have been used, including photographic film, multiwire gas proportional counters and large area CCD detectors, the latter having a 2-D spatial resolution of 22.5 μm (1152×1242 pixels, 26×28 mm2), a quantum efficiency greater than 20% between 0.7 and 12 keV and an energy resolution of about 150 eV. By sacrificing energy resolution, a one-dimensional mode with on-chip binning allows ∼ms time resolution of spectra from high flux sources such as tokamaks and synchrotrons. Results presented include photographic spectra from tokamak, beam foil and laser produced sources, and CCD spectra from tokamak and standard electron-beam excitation laboratory sources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143478
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  • 9
    Electronic Resource
    Electronic Resource
    A novel multichord spectrometer for plasma velocity measurements : 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. 5164-5166 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A diagnostic has been designed to study edge plasma velocities in (JET) with good space and time resolution. To eliminate ambiguities in the measurement arising from atomic physics effects opposing views are provided. Each viewing direction incorporates ten fibers imaged on the path of a neutral heating beam with a channel spacing of 1.5 cm. The chord views are imaged onto a spectrometer with 20 individual entrance slits arranged in a rectangular array. The dispersed spectra from adjacent slits form linear images 25 mm long that are recorded using four fast optical multichannel analyzers. To prevent crosstalk of signals from adjacent slits the instrument incorporates a low dispersion spectrometer to limit the bandpass of the system. The principal advantage of this design is the ability to match the f number of the fiber optic arrays. This results from the rectangular arrangement of the slits which allows for a 4× magnification of the fiber images without requiring an exceptionally long (70 mm) entrance slit. This matching optimises the light collection efficiency of the complete diagnostic which ultimately sets the shortest time resolution. The minimum readout time for all 20 channels is 0.5 ms, although longer integration times are generally needed in JET.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143468
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  • 10
    Electronic Resource
    Electronic Resource
    Quantitative spectroscopy of x-ray lines and continua in Tokamaks (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1734-1738 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Crystal and synthetic multilayer diffractors, deployed either as flat Bragg reflectors, or curved, as in the Johann configuration, are used to study the spectrum of COMPASS-D and other tokamaks in the wavelength region of 1–100 Å. In this article, we concentrate on the measurement of absolute photon fluxes and the derivation of volume emissivities of the lines and continua in the x-ray region. The sensitivities of these instruments to absolute photon flux have been constructed ab initio from the individual component efficiencies, including published values of the diffractor reflectivities, which have been checked or supplemented by measurements using a double-axis goniometer or from line branching ratios. For those tokamak plasmas, where the elemental abundances and effective ion charge are documented, the x-ray continuum intensity itself has been used as a calibration source to derive absolute instrument sensitivity, in reasonable agreement with the ab initio method. In the COMPASS-D Tokamak, changes in the effective ion charge state, Zeff, have been derived for different operating conditions, from the absolute intensity of the continuum at ∼4 Å. From the radiances of the line emission, changes in the absolute level of impurities following "boronization" of the vacuum vessel have also been documented. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147983
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