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  • 1
    Electronic Resource
    Electronic Resource
    Observation of wall stabilization and active control of low-n magnetohydrodynamic instabilities in a tokamak (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1926-1934 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The High Beta Tokamak-Extended Pulse (HBT-EP) experiment [J. Fusion Energy 12, 303 (1993)] combines an internal, movable conducting wall with a high-power, modular saddle coil system to provide passive and active control of long wavelength magnetohydrodynamic (MHD) instabilities. Systematic adjustment of the radial position, b, of the conducting wall elements in relation to the surface of the plasma (minor radius a) resulted in the suppression of β-limiting disruptions for discharges in which b/a〈1.2 and a positive plasma current ramp was maintained. Conducting wall stabilization of kink instabilities was observed in discharges with strong current ramps and in plasmas with β values near the Troyon stability boundary. The frequency of slowly growing modes that persisted in wall-stabilized discharges was controlled by applying oscillating m=2, n=1 resonant magnetic perturbations. A compact, single-phase saddle coil system permitted modulation of the rotation velocity of internal m/n=2/1 instabilities by a factor of 2. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871988
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  • 2
    Electronic Resource
    Electronic Resource
    Development of a transient internal probe diagnostic : 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. 5148-5150 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The transient internal probe (TIP) diagnostic is a novel method for probing the interior of hot magnetic fusion plasmas. In the TIP scheme, a probe is fired, using a two-stage light gas gun, through a hot plasma at velocities up to 5 km/s, and makes direct, local measurements of the internal magnetic field structure. The data are relayed to the laboratory optical detection system using an incident laser that is directed through a Faraday rotator payload acting as a magneto-optic sensor. Ablative effects are avoided by minimizing the probe size, limiting the time that the probe is in the hot plasma, and encasing the probe with a diamond cladding. The degree to which the diamond probe cladding is susceptible to ablative effects will determine the plasma density and temperature regime in which the TIP diagnostic can be used. If the TIP suffers significant ablation it is an indication that the diagnostic is not usable on this hot and dense of a plasma (or that greater velocity must be imparted to the probe to further minimize the time that it is in the plasma). A quantitative experimental study of the ablation rates of diamond is planned as part of the TIP development. The integrated TIP system will be functional in 1992 and installed on the Helicity Injected Torus (HIT) [T. R. Jarboe, Fusion Tech. 15, 9 (1989)] at the University of Washington.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143812
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  • 3
    Electronic Resource
    Electronic Resource
    Wideband "silicon bolometers'' on the LSX field reversed configuration experiment : 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. 4717-4719 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Silicon photodiode detectors, which have nearly flat energy response from 1 eV to 6 keV [R. Korde and L. Randall Canfield, Proc. SPIE 1140, 126 (1989)], were used as bolometers in the field reversed theta pinch experiment LSX. Plasma escaping from the field reversed configuration is naturally diverted to the ends of the vacuum enclosure. There it affects the bolometer measurements either by direct energy deposition or by emission of low energy photons. These two particle effects can be avoided by optimizing the location of the bolometers and restricting their field of view. Good agreement is observed between the silicon bolometers and a gold foil calorimeter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143617
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  • 4
    Electronic Resource
    Electronic Resource
    Digital-image capture system for the IR camera used in Alcator C-Mod : 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. 927-930 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An infrared imaging system, based on an Amber Radiance 1 infrared camera, is used at Alcator C-Mod to measure the surface temperatures in the lower divertor region. Due to the supra-linear dependence of the thermal radiation with temperature it is important to make use of the 12-bit digitization of the focal plane array of the Amber camera and not be limited by the 8 bits inherent to the video signal. It is also necessary for the image capture device (i.e., fast computer) to be removed from the high magnetic field environment surrounding the experiment. Finally, the coupling between the digital camera output and the capture device should be nonconductive for isolation purposes (i.e., optical coupling). A digital video remote camera interface (RCI) coupled to a PCI bus fiber optic interface board is used to accomplish this task. Using this PCI-RCI system, the 60 Hz images from the Amber Radiance 1 camera, each composed of 256×256 pixels and 12 bits/pixel, are captured by a Windows NT computer. An electrical trigger signal is given directly to the RCI module to synchronize the image stream with the experiment. The RCI can be programmed from the host computer to work with a variety of digital cameras, including the Amber Radiance 1 camera.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321008
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  • 5
    Electronic Resource
    Electronic Resource
    The new infrared imaging system on Alcator C-Mod : 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. 734-737 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new infrared imaging system has been installed on Alcator C-Mod. This system uses an Amber Radiance 1 IR video camera (filtered to the 4.2–4.4 μm band) to view a 30 cm×30 cm region of the lower divertor from above by means of a re-entrant 5-m long ZnSe based periscope. Capture of the standard 30 Hz video frames (8-bit) and camera control are performed remotely over fiber optic links by a Windows 95 PC, using a MuTech MV-1000 video grabber board. Plans are under way to directly capture the 60 Hz, 12-bit, 256×256 pixel images using a digital video camera interface with a fiber optic link from EDT (Beaverton, Oregon). Preliminary results show that during nondisruptive discharges no substantial surface temperature increase is observed on the upper sections of the divertor, with the exception of "hot spots," although occasionally, increased heating in toroidal bands is seen. Bands can also be observed after disruptions that result in a downward movement of the plasma. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149496
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  • 6
    Electronic Resource
    Electronic Resource
    High resolution observations of pellet emission on TFTR (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. 841-841 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High resolution, rapidly sampled measurements of the light emission from injected impurity pellets have recently been carried out on TFTR. Both wide and narrow views of the pellet light have been accomplished with a tightly collimated fanned array of fiber-optically coupled photomultipliers. Deep (≈100%), high frequency (40–90 kHz) modulation of the pellet emission has been observed in both neutral beam and rf heated discharges with as little as ≈1.5 MW of heating. This finding is consistent with recent work carried out on ASDEXb) with the exception that this modulation phenomenon is seen not only with hydrogenic pellets but also with lithium and boron pellets. This observation seems to point to an instability associated with the plasma surrounding the pellet rather than an instability which depends upon the atomic physics of the pellet. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146243
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  • 7
    Electronic Resource
    Electronic Resource
    Design of an imaging bolometer system for the large helical device : 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. 766-769 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a radical design for a bolometer system employing infrared (IR) imaging of a segmented-matrix absorber in a cooled-pinhole camera geometry, which we will prototype and demonstrate on the large helical device (LHD).1 LHD will be operational in early 1998, with an l=2 superconducting winding, a major radius of 3.9 m, a minor radius of 0.5–0.65 m, and input powers ranging from 3 MW (steady state) to 30 MW (pulsed). The bolometer design parameters are determined by modeling the temperature of the foils making up the detection matrix using a two-dimensional time-dependent solution of the heat conduction equation. This design will give a steady-state bolometry capability, with modest (60 Hz) time resolution, while simultaneously providing hundreds of channels of spatial information. No wiring harnesses will be required, as the temperature-rise data is measured via a 12-bit, ±0.025 °C resolution, 3–5 μm band, 256×256 pixel IR camera. The spatial data will be used to tomographically invert the profile of the highly shaped stellarator main plasma and divertor radiation, in conjunction with more conventional fanned arrays of traditional bolometers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147693
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  • 8
    Electronic Resource
    Electronic Resource
    Edge turbulence measurements in NSTX by gas puff imaging : 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. 931-934 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Turbulent filaments in visible light emission corresponding mainly to density fluctuations at the edge have been observed in large aspect ratio tokamaks: TFTR, ASDEX, Alcator C-Mod, and DIII-D. This article reports on similar turbulent structures observed in the National Spherical Torus Experiment (NSTX) using a fast-framing, intensified, digital visible camera. These filaments were previously detected mainly in high recycling regions, such as at limiters or antennas, where the line emission from neutral atoms was modulated by the fluctuations in local plasma density. However, by introducing controlled edge gas puffs, i.e., gas puff imaging, we have increased the brightness and contrast in the fluctuation images and allowed the turbulent structure to be measured independently of the recycling. A set discrete fiber-optically coupled sight-lines also measured the frequency spectra of these light fluctuations with a 200 kHz bandwidth. Initial results in NSTX show that the turbulent filaments are well aligned with the magnetic field which can be up to 45° from the horizontal at the outer midplane of NSTX. The dominant wavelength perpendicular to the magnetic field is ∼7–11 cm, corresponding to a k⊥ ρs of ∼0.3 at an assumed Te=25 eV, and the frequency spectra has a typical broad shape characteristic of edge turbulence extending to about 100 kHz. By imaging a He gas puff along a magnetic field line the characteristic radial scalelength appears to be in the 3–5 cm range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1321009
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  • 9
    Electronic Resource
    Electronic Resource
    Density and Hα diagnostics and results for the sustained spheromak physics experiment : 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. 1059-1062 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A newly installed density diagnostic using CO2 laser interferometry and an Hα diagnostic using interference filters and photomultiplier tubes for the recently constructed sustained spheromak physics experiment (SSPX) are described. First diagnostic results of the Hα diagnostic were useful to understand the breakdown physics in the new SSPX experiments. Low-noise density data validates techniques to reduce vibration and electronic pickup. The data-processing electronics of the new interferometer can yield unambiguous density data that is equivalent to 16 fringe shifts. Density data is also critical to understand the particle source, and the J/ne parameter for SSPX.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319364
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  • 10
    Electronic Resource
    Electronic Resource
    Development of imaging bolometers for long-pulse MFE experiments (invited) : 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. 255-259 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed the concept of an imaging bolometer, capable of operation with 100's of individual channels, while relying on optical (infrared) readout of the temperature rise in a thin foil. A thin gold foil (0.5–5 μm thick) is sandwiched between pieces of copper. The copper mask (a large thermal mass) has a hole pattern drilled into it to form many "individual pixels," effectively forming many separate sensors. This segmented foil/mask combination is exposed on its front side to plasma radiation through a cooled pinhole camera geometry. Simultaneously, a high-resolution infrared camera monitors any temperature change on the backside of the thin foil. A sensitive infrared (IR) camera views the foil through an IR telescope/periscope system, and is shielded from the magnetic and nuclear radiation fields, either by distance and/or material shielding. A simple time-dependent design algorithm, using 1D heat transport to a cold boundary, has been written in MathCad, which allows us to select optimal material and geometries to match the expected plasma conditions. We have built a compact prototype with 149 channels, and tested it successfully both in a vacuum test stand in the laboratory, and on a plasma in the CHS at the National Institute for Fusion Science, subjecting it to electron cyclotron heated and neutral beam injection heated conditions. A water-cooled version has been built for the new LHD. Since the IR imaging bolometer uses only metal parts near the plasma, and has no need for wiring or wiring feedthrus, it is intrinsically radiation hard, and has direct application to ignition device to test engineering concepts (ITER), or ITER-class experiments. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149441
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