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  • 1
    Electronic Resource
    Electronic Resource
    E×B circulation at the tokamak divertor X point : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2118-2124 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed measurements in two dimensions by probes and Thomson scattering reveal unexpected local electric potential and electron pressure (pe) maxima near the divertor X point in L-mode plasmas in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)]. The potential drives E×B circulation about the X point, thereby exchanging plasma between closed and open magnetic surfaces at rates that can be comparable to the total cross-separatrix transport. The potential is consistent with the classical parallel Ohm's law. A simple model is proposed to explain the pressure and potential hills in low power, nearly detached plasmas. Recent two-dimensional edge transport modeling with plasma drifts also shows X-point pressure and potential hills but by a different mechanism. These experimental and theoretical results demonstrate that low power tokamak plasmas can be far from poloidal uniformity in a boundary layer just inside the separatrix. Additional data, although preliminary and incomplete, suggest that E×B circulation across the separatrix might be a common feature of low confinement behavior. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1352597
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  • 2
    Electronic Resource
    Electronic Resource
    Spectroscopic determinations of carbon fluxes, sources, and shielding in the DIII-D divertors (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4470-4482 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The most important mechanisms for eroding plasma-facing components (PFCs) and introducing carbon into tokamak divertors are believed to be physical sputtering, chemical sputtering, sublimation, and radiation enhance sublimation (RES). The relative importance of these processes has been investigated by analyzing the spectral emission rates and the effective temperatures of CI, CD, and C2 under several operating conditions in the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEEE/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrical and Electronic Engineers, Piscataway, 1999), p. 515]. Discrimination of chemical sputtering from physical sputtering is accomplished by quantitatively relating the fraction of CI influxes expected from dissociation of hydrocarbons to the measured CD and C2 influxes. Characteristics of sublimation are studied from carbon test samples heated to surface temperatures exceeding 2000 K. The shielding efficiency of carbon produced at the divertor target is assessed from comparison of fluxes of neutral atoms and ions; approximately 95% of the primary influx appears to be redeposited before being transported far enough upstream to fuel the core plasma. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1403416
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  • 3
    Electronic Resource
    Electronic Resource
    Drift-wave-like density fluctuations in the Advanced Toroidal Facility (ATF) torsatron (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 398-413 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Density fluctuations in low-collisionality, low-beta (β∼0.1%), currentless plasmas produced with electron cyclotron heating (ECH) in the Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)] have been studied using a 2 mm microwave scattering diagnostic. Pulsed gas puffing is used to produce transient steepening of the density profile from its typically flat shape; this leads to growth in the density fluctuations when the temperature and density gradients both point in the same direction in the confinement region. The wave number spectra of the fluctuations that appear during this perturbation have a maximum at higher k⊥ρs (∼1) than is typically seen in tokamaks. The in–out asymmetry of the fluctuations along the major radius correlates with the distribution of confined trapped particles expected for the ATF magnetic field geometry. During the perturbation, the relative level of the density fluctuations in the confinement region (integrated over normalized minor radii ρ from 0.5 to 0.85) increases from ñ/n∼1% when the density profile is flat to ñ/n∼3% when the density profile is steepened. These observations are in qualitative agreement with theoretical expectations for helical dissipative trapped-electron modes (DTEMs), which are drift-wave instabilities associated with particle trapping in the helical stellarator field; they suggest that trapped-electron instabilities may play a role in constraining the shape of the density profile in ATF, but have little effect on global energy confinement. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870966
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  • 4
    Electronic Resource
    Electronic Resource
    Long pulse experiments on the Advanced Toroidal Facility (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2435-2439 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Advanced Toroidal Facility (ATF) [Fusion Technol. 10, 179 (1986)] is the world's largest stellarator. It was designed and built to demonstrate high beta, steady-state operation in a toroidal confinement system. During its final operating period ATF achieved pulse lengths of over one hour (4667 s). The objectives of these experiments were (1) investigation of plasma performance at times that are long compared to the plasma/wall equilibrium time; (2) determination of plasma control and wall conditioning techniques; and (3) adaptation of plasma diagnostic and data acquisition systems to long-pulse operation. Other experiments have also extended earlier studies of dimensionless-parameter plasma confinement scaling. By employing two discrete electron cyclotron heating (ECH) frequencies (28 and 35 GHz), and by simultaneously modulating the ECH power, magnetic field, and plasma density, it has been possible to maintain fixed plasma beta and collisionality while modulating the normalized gyroradius. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871267
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  • 5
    Electronic Resource
    Electronic Resource
    Possible integrated diagnostic set for ion cyclotron heating for the tokamak physics experiment (TPX) (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. 866-866 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Heating and current drive with ICRF is one of the major missions of TPX and is crucial to its success. In contrast to the integrated nature of core diagnostic programs, diagnostics that measure ICRF propagation and edge interactions are often assigned lower priority, have not been included in the base diagnositics set, or were included as upgrades. This can result in an incomplete and unoptimized set of measurements. Thus it is important that an integrated set of diagnostics (engineered along with the antenna design), capable of fully diagnosing the interaction, propagation, and absorption of the ICRF be available for TPX. The parameters of interest include: coupling of the ICRF antenna to the plasma, launched spectrum, wave propagation, edge plasma interactions, electron heating, and current drive, and fast ion power deposition and losses. The diagnostic set should be designed so it can be upgraded for control of loading and spectrum by providing feedback information for adjusting phase, power level, fuel gas injection, and plasma position. The proposed set focuses on wave propagation, launched spectrum, absorption, and measuring and comparing the plasma edge properties in the near vicinity of the antenna with that measured at a large toroidal distance from them; thus many would be installed as toroidally separated indentical sets. In addition to the planned core diagnostic set, the ICRF specific diagnostics proposed for TPX include: edge density reflectometers, RF fluctuation reflectometers, fixed and moveable Langmuir probes, visible and IR cameras with spectroscopic line filters, rf magnetic loop probes, local ion energy analyzer, direct ion loss detectors, charge exchange analyzers, fast response ECE, and edge temperature ECE. The anticipated approach is one in which individual diagnostics could be provided by industry, universities, or laboratories but overall coordination, driven by specific ICRF issues, would be required. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146425
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  • 6
    Electronic Resource
    Electronic Resource
    Electron beam and magnetic field mapping techniques used to determine field errors in the ATF torsatron (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2680-2689 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The beam from an electron gun was used to trace flux surfaces in the Advanced Toroidal Facility (ATF) torsatron. The ATF magnetic field was run steady state at 0.1 T, and the electron beam was detected optically with an image-intensified, solid-state camera when it impinged on a phosphor-coated screen. Closed flux surfaces and islands at several low-order resonances were observed. The largest island, located at the ι= 1/2 surface, was from 5 to 6 cm in width, and its presence implied the existence of magnetic field errors. To determine if these error fields could be traced to small misalignments of the magnetic coils, a device capable of accurately measuring the radial and vertical magnetic field components of individual coil sets was placed in the center of ATF. This device allowed for a determination of the precise location of each of the coils that make up the ATF coil set. No significant coil misalignments were found. A further investigation of the coil configuration led to the identification of dipole fields in the helical field coil leads as the source of the field errors. The techniques developed in making these measurements are described in the text.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141082
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  • 7
    Electronic Resource
    Electronic Resource
    Accurate electron gun-positioning mechanism for electron beam-mapping of large cross-section magnetic surfaces (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 795-797 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method of accurately supporting and positioning an electron source inside a large cross-sectional area magnetic field which provides very low electron beam occlusion is reported. The application of electrical discharge machining to the fabrication of a 1-m truss support structure has provided an extremely long, rigid and mechanically strong electron gun support. Reproducible electron gun positioning to within 1 mm has been achieved at any location within a 1×0.6-m2 area. The extremely thin sections of the support truss (≤1.5 mm) have kept the electron beam occlusion to less than 3 mm. The support and drive mechanism have been designed and fabricated at the University of Wisconsin for application to the mapping of the magnetic surface structure of the Advanced Toroidal Facility torsatron1 at the Oak Ridge National Laboratory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141024
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  • 8
    Electronic Resource
    Electronic Resource
    Charge exchange stripping cell measurements over a wide pressure range (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1667-1669 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The efficiency of the stripping cell incorporated in a charge exchange analyzer has been measured over a pressure range of 1.8–130 mTorr and over an energy range of 1–130 keV/amu. In these measurements, a beam of hydrogen atoms was ionized by helium gas. As a by-product of the measurements, the scattering cross section was also measured. At the lowest pressure, the scattering cross section compared well with those measured previously; at high pressure, the cross section no longer followed an energy power law. The analyzer efficiency (defined as the fraction of the atoms that is ionized and not lost through scattering) can be modeled over the entire range of energy and pressure by including the measured scattering cross sections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140127
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic surface mapping with highly transparent screens on the Auburn torsatron (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 460-466 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In stellarator-type magnetic confinement devices (of which the torsatron is one), the magnetic field is produced entirely by external, current-carrying coils. Two methods for mapping magnetic surfaces in the Auburn torsatron were tested and compared, both of which involve the use of highly transparent screens. The first method consists of coating the screen with a phosphor that emits light when struck by electrons emitted by an electron gun. A pattern representative of a magnetic surface is formed on the screen, and this pattern is recorded photographically. The second method uses an uncoated screen to collect electrons emitted from an emissive probe, which is scanned over a poloidal cross section of the torus. Under certain conditions, the collected current is a constant over a particular magnetic surface so that a contour plot of the current versus position is equivalent to a plot of the magnetic surfaces. Parametric studies of the two methods are presented, and the effectiveness of each technique is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139861
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  • 10
    Electronic Resource
    Electronic Resource
    Diagnostic applications of the TFTR XIS system (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2136-2138 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The horizontal x-ray imaging system (XIS) on the tokamak fusion test reactor (TFTR) tokamak is an array of 64 silicon surface-barrier x-ray diodes, with a 2.5-cm spatial resolution. The XIS system is primarily used to study magnetohydrodynamic (MHD) instabilities, but has also been used to measure electron thermal diffusivity, electron temperature, the radius of the q=1 surface, plasma vertical position, and toroidal rotation of the plasma. Movable absorber-foil arrays provide energy selection. Bandpass analog filters and digital techniques have been used on the x-ray signals in an attempt to infer turbulence levels in the plasmas. Details of the above techniques will be presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138709
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