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  • 1
    Electronic Resource
    Electronic Resource
    Operation of a multichannel tangential bolometer on PBX (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2099-2099 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A compact 15-channel bolometer array that views plasma emission tangentially across the midplane has been installed on the PBX tokamak to supplement a 19-channel radially viewing poloidal array. By comparing these diagnostics, poloidal asymmetries in the emission profile can be determined. The detector array consists of 15 discrete 2-mm-diam thinistors, a mixed semiconductor material, which has a high temperature coefficient of resistance. Each active detector is operated in tandem with an identical blind detector in a Wheatstone bridge configuration. The variation in voltage owing to the change in resistance is amplified and stored on a CAMAC transient recorder. The detectors are sensitive to accumulated heat and software has been written to smooth and differentiate the signals so that instantaneous power can be calculated. In addition, the cooling time constants are determined in vacuo (3.1 s) so that the loss of heat from the detector during the course of a shot can be compensated. The detectors were relatively calibrated with a tungsten–halogen filament lamp and were found to vary by ±7%. The irradiance profiles are inverted and the power density is typically in the 0.1 to 0.5-W/cm3 range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138751
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  • 2
    Electronic Resource
    Electronic Resource
    Charge exchange recombination spectroscopy measurements of ion temperature and plasma rotation in PBX (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 865-867 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The primary diagnostic on PBX for ion temperature measurements is charge exchange recombination spectroscopy of low Z ions, wherein fast neutrals from the heating neutral beams excite spectral lines from highly excited states (n〉4) of hydrogenic O, C, and He via charge exchange collisions with the respective fully stripped ions. Since the neutral beams on PBX provide relatively low-velocity neutrals (i.e., D° beams at 44 keV), best signals are obtained using the near-UV lines of O7+ (e.g., n=8–7, 2976 A(ring)). Off-line analysis of the Doppler broadened and shifted line profiles includes nonlinear least-squares fitting to a model line profile, while a simplified on-line fast analysis code permits between-shot data analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138075
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  • 3
    Electronic Resource
    Electronic Resource
    Utilization of charge exchange recombination spectroscopy for the study of metallic ion transport in TFTR (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1518-1520 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Charge exchange recombination spectroscopy has been used to observe transitions originating from hydrogen-, helium-, and lithiumlike charge states of medium-Z metallic impurities in TFTR. The temporal and spatial densities of these ions were measured in ohmic and neutral beam heated plasmas. These preliminary results agree with predictions of a transport code.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140182
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  • 4
    Electronic Resource
    Electronic Resource
    Corrections to charge exchange spectroscopic measurements in TFTR due to energy-dependent excitation rates (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1521-1523 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The use of charge exchange spectroscopy to determine plasma rotation speeds and ion temperature is complicated by the energy dependence of the excitation cross sections. The Doppler-broadened spectral line shape is distorted by the relative velocity between the neutral hydrogen atoms of the injected beam and impurity ions. The asymmetric nature of the energy dependence of this cross section causes a nonmotional shift of the line center and a nonthermal change in the linewidth. These effects vary with the angles between the beam direction, rotation velocity direction, and direction of the viewing sightline. When viewing two neutral beams at different angles on TFTR, the two measurements of vφ(r) show discrepancies of about 20%–30% with each other. The calculation of the spectral intensity profiles using the available excitation rates overcorrects these discrepancies and indicates the need for better excitation coefficients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140183
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  • 5
    Electronic Resource
    Electronic Resource
    Species and divergence measurements on the TFTR diagnostic neutral beam (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1676-1678 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The ion source of the TFTR diagnostic neutral beam utilizes a magnetic cusp bucket from a PLT source modified with an internal rf antenna in place of filaments. The species mix of the beam has been measured after the neutralizer as a function of several parameters in two ways: spectroscopically and by an electrostatic charge exchange analyzer. Source and neutralizer gas feeds (both hydrogen) were varied. Some measurements were made with the bending magnet alternately on and off to obtain neutralizer efficiency for each component. Accelerator current was varied, at fixed acceleration voltage and gas feed rate, by varying rf power to the antenna. Relative beam divergence during this scan was monitored by both diagnostics, and an absolute divergence was obtained from a spectroscopic profile scan.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140130
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  • 6
    Electronic Resource
    Electronic Resource
    Tomographic imaging of MHD activity in tokamaks by combining diode arrays and a tangentially viewing pinhole camera (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1819-1821 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two 32-channel side-viewing soft x-ray diode arrays will be installed on PBX-M which will provide profile information in the horizontal and vertical directions with a time resolution up to 1 μs. The information from these arrays can be reconstructed to provide a high time-resolution poloidal emission profile using a maximum-entropy-based technique which incorporates the reconstructed profile from a tangentially viewing soft x-ray pinhole camera. The pinhole camera provides lower time-resolution (about 5 ms) shape information which has been reconstructed with the assumption of toroidal symmetry. The pinhole camera information supplements the information from the diode arrays, allowing a reconstruction which can resolve MHD fluctuations of the equilibrium profile. The pinhole camera information need only be a better approximation to the real emission profile than the assumption of a flat profile since the algorithm uses it as a first-order solution which is perturbed by the information from the diode arrays. The algorithm can also explicitly include the bean-shaped PBX-M vacuum vessel and the vignetting of some detectors by the pusher coil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140070
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  • 7
    Electronic Resource
    Electronic Resource
    Soft-x-ray camera for internal shape and current-density measurements on a noncircular tokamak (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1831-1833 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A two-dimensional, tangentially viewing, soft-x-ray pinhole camera has been fabricated to provide internal shape measurements on the PBX-M tokamak. It consists of a scintillator at the focal plane of a foil-filtered pinhole camera, which is, in turn, fiber-optically coupled to an intensified framing video camera (Δt≥3 ms). Automated data acquisition is performed on a stand-alone image processing system, and data archiving and retrieval take place on an optical disk video recorder. The derivation of the poloidal emission distribution from the measured image is done by fitting to model profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140074
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  • 8
    Electronic Resource
    Electronic Resource
    Impurity-induced turbulence suppression and reduced transport in the DIII-D tokamak : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1870-1877 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Long wavelength turbulence as well as heat and momentum transport are significantly reduced in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] as a result of neon seeding of a low confinement mode negative central shear discharge. Correspondingly, the energy confinement time increases by up to 80%. Fully saturated turbulence measurements near ρ=0.7 (ρ=r/a) in the wave number range 0.1≤k⊥ρs≤0.6, obtained with beam emission spectroscopy, exhibit a significant reduction of fluctuation power after neon injection. Fluctuation measurements obtained with far infrared scattering also show a reduction of turbulence in the core, while the Langmuir probe array measures reduced particle flux in the edge and scrape-off layer. Gyrokinetic linear stability simulations of these plasmas are qualitatively consistent, showing a reduction in the growth rate of ion temperature gradient driven modes for 0〈k⊥ρs≤1.4, and nonlinear gyrokinetic simulations show a reduced saturated density fluctuation amplitude. The measured ωE×B shearing rate increased at ρ=0.7, suggesting that impurity-induced growth rate reduction is acting synergistically with ωE×B shear to decrease turbulence and reduce anomalous transport. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874010
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  • 9
    Electronic Resource
    Electronic Resource
    Convergence, electrostatic potential, and density measurements in a spherically convergent ion focus (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4-15 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Unique measurements of the basic plasma-flow characteristics in a low pressure (≤53 mPa H2) spherically convergent ion focus are obtained using high-voltage (≤5 kV) emissive and double probes. The radial plasma potential distribution agrees with a collisionless, recirculating, space-charge-limited current model. Flow convergence increases with voltage and neutral pressure and decreases with cathode grid wire spacing and current. Core radii within 4–5 times the ideal geometric limit are measured, and the observed core sizes are consistent with predictions from a multipass orbit model which includes asymmetries in the accelerating potential well. A virtual anode is observed in the converged core region, and no evidence for multiple potential well structures in the core is found. Measurements of the core ion density (nic∼1015 m−3) are consistent with simple flow convergence models. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872110
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  • 10
    Electronic Resource
    Electronic Resource
    Technique for the experimental estimation of nonlinear energy transfer in fully developed turbulence (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3998-4009 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new procedure for calculating the nonlinear energy transfer and linear growth/damping rate of fully developed turbulence is derived. It avoids the unphysically large damping rates typically obtained using the predecessor method of Ritz [Ch. P. Ritz, E. J. Powers, and R. D. Bengtson, Phys. Fluids B 1, 153 (1989)]. It enforces stationarity of the turbulence to reduce the effects of noise and fluctuations not described by the basic governing equation, and includes the fourth-order moment to avoid the closure approximation. The new procedure has been implemented and tested on simulated, fully developed two-dimensional (2-D) turbulence data from a 2-D trapped-particle fluid code, and has been shown to give excellent reconstructions of the input growth rate and nonlinear coupling coefficients with good noise rejection. However, in the experimentally important case where only a one-dimensional (1-D) averaged representation of the underlying 2-D turbulence is available, this technique does not, in general, give acceptable results. A new 1-D algorithm has thus been developed for analysis of 1-D measurements of intrinsically 2-D turbulence. This new 1-D algorithm includes the nonresonant wave numbers in calculating the bispectra, and generally gives useful results when the width of the radial wave number spectrum is comparable to or less than that of the poloidal spectrum. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871572
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