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  • 1
    Electronic Resource
    Electronic Resource
    TFTR Mirnov loop system (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2084-2086 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Magnetic pick-up loops (Mirnov coils) located on the inner wall of the tokamak fusion test reactor (TFTR) vacuum vessel have been used to study magnetic fluctuations in the plasma. To study the high-frequency magnetic turbulence associated with beam injection, the signal from one coil is passed through a comb filter, which gives a measure of the frequency spectrum throughout the shot. To look for tearing modes, the signals from a poloidal array of 15 coils are summed in an analog system to give the amplitudes of the m=2, 3, and 4 coherent modes throughout the shot. Additionally, 20 coil signals are digitized individually at a rate of 100 kHz for 80 ms and at 10 kHz for 800 ms. These data may also be analyzed off line to get both the toroidal and poloidal mode numbers as well as the frequency spectrum for a limited portion of the discharge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138746
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Heat pulse propagation studies on DIII-D and the Tokamak Fusion Test Reactor (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 5051-5063 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sawtooth phenomena have been studied on DIII-D and the Tokamak Fusion Test Reactor (TFTR) [D. Meade and the TFTR Group, in Proceedings of the International Conference on Plasma Physics and Controlled Nuclear Fusion, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, pp. 9–24]. In the experiments the sawtooth characteristics were studied with fast electron temperature (ECE) and soft x-ray diagnostics. For the first time, measurements of a strong ballistic electron heat pulse were made in a shaped tokamak (DIII-D) [J. Luxon and DIII-D Group, in Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Kyoto (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] and the "ballistic effect" was stronger than was previously reported on TFTR. Evidence is presented in this paper that the ballistic effect is related to the fast growth phase of the sawtooth precursor. Fast, 2 ms interval, measurements on DIII-D were made of the ion temperature evolution following sawteeth and partial sawteeth to document the ion heat pulse characteristics. It is found that the ion heat pulse does not exhibit the very fast, "ballistic" behavior seen for the electrons. Further, for the first time it is shown that the electron heat pulses from partial sawtooth crashes (on DIII-D and TFTR) are seen to propagate at speeds close to those expected from the power balance calculations of the thermal diffusivities whereas heat pulses from fishbones propagate at rates more consistent with sawtooth induced heat pulses. These results suggest that the fast propagation of sawtooth-induced heat pulses is not a feature of nonlinear transport models, but that magnetohydrodynamic events can have a strong effect on electron thermal transport. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319335
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  • 4
    Electronic Resource
    Electronic Resource
    Nonlinear evolution of double tearing modes in tokamaks (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4112-4120 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Δ′ formalism with neoclassical modifications has proven to be a useful tool in the study of tearing modes in high β, collisionless plasmas. In this paper the formalism developed for the inclusion of neoclassical effects on tearing modes in monotonic q-profile plasmas is extended to plasmas with hollow current profiles and double rational surfaces. First, the classical formalism of tearing modes in the Rutherford regime in low beta plasmas is extended to q profiles with two rational surfaces and it is shown that this formalism is readily extended to include neoclassical effects. The evolution of a double tearing mode on the Tokamak Fusion Test Reactor is then simulated. Reasonable agreement is found for the outer island, but the stabilizing effect of the neoclassical term is overly large for the inner island. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289893
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of modes at frequencies near the second Alfvén gap in the Tokamak Fusion Test Reactor (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4121-4125 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modes have been observed near the frequency of the second Alfvén gap during off-axis H-minority heating experiments in the circular cross-section Tokamak Fusion Test Reactor. The observation of these modes is surprising in that the second gap, which is generally opened with ellipticity, is expected to be small, of order (r/R)2. A model is proposed in which the second gap is opened by the fast ion beta, which is shown to be able to introduce mode coupling, much as toroidal effects introduce mode coupling for Toroidal Alfvén Eigenmodes (TAE). With the low inferred energy of the fast ion tail (30–50 keV), the fast ion bounce resonance condition is assumed to drive the modes. The modes are seen with and without accompanying TAE mode activity. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289894
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of the structure of magnetic islands on TFTR (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1797-1800 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Mirnov coil array, the horizontal soft x-ray camera, and the ECE (electron cyclotron emission) grating polychromator are used to unfold the structure of m≥2 coherent magnetic fluctuations (assumed to be tearing modes) observed in TFTR. The modes are found predominantly in the enhanced confinement, or supershot, regime, and when present seriously degrade confinement. The poloidal and toroidal mode numbers (m and n) are determined with the Mirnov coil array. The radial structure is found by calculating the theoretical radial eigenmode (based on the calculated current-density profile) and scaling the resulting linear eigenmode with the measured fluctuation amplitude at the plasma edge. The presence of rotating magnetic islands is detected as fluctuations on both the chord-averaged soft-x-ray emissivity measurements and the fast grating polychromator electron temperature measurements. The ECE and soft-x-ray systems are used to identify coherent modes as islands and confirm estimates of the islands' location inferred from the Mirnov coil data and calculated current-density profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140116
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  • 7
    Electronic Resource
    Electronic Resource
    Active feedback stabilization of the resistive wall mode on the DIII-D device : 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. 2071-2082 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A proof of principle magnetic feedback stabilization experiment has been carried out to suppress the resistive wall mode (RWM), a branch of the ideal magnetohydrodynamic (MHD) kink mode under the influence of a stabilizing resistive wall, on the DIII-D tokamak device [Plasma Phys. Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159; Phys. Plasmas 1, 1415 (1994)]. The RWM was successfully suppressed and the high beta duration above the no-wall limit was extended to more than 50 times the resistive wall flux diffusion time. It was observed that the mode structure was well preserved during the time of the feedback application. Several lumped parameter formulations were used to study the feedback process. The observed feedback characteristics are in good qualitative agreement with the analysis. These results provide encouragement to future efforts towards optimizing the RWM feedback methodology in parallel to what has been successfully developed for the n=0 vertical positional control. Newly developed MHD codes have been extremely useful in guiding the experiments and in providing possible paths for the next step. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1351823
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  • 8
    Electronic Resource
    Electronic Resource
    Initial physics results from the National Spherical Torus Experiment : 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. 1977-1987 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mission of the National Spherical Torus Experiment (NSTX) is to extend the understanding of toroidal physics to low aspect ratio (R/a(similar, equals)1.25) in low collisionality regimes. NSTX is designed to operate with up to 6 MW of high harmonic fast wave (HHFW) heating and current drive, 5 MW of neutral beam injection (NBI) and co-axial helicity injection (CHI) for noninductive startup. Initial experiments focused on establishing conditions that will allow NSTX to achieve its aims of simultaneous high βt and high-bootstrap current fraction, and to develop methods for noninductive operation, which will be necessary for Spherical Torus power plants. Ohmic discharges with plasma currents up to 1 MA and with a range of shapes and configurations were produced. Density limits in deuterium and helium reached 80% and 120% of the Greenwald limit, respectively. Significant electron heating was observed with up to 2.3 MW of HHFW. Up to 270 kA of toroidal current for up to 200 ms was produced noninductively using CHI. Initial NBI experiments were carried out with up to two beam sources (3.2 MW). Plasmas with stored energies of up to 140 kJ and βt=21% were produced. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1343089
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  • 9
    Electronic Resource
    Electronic Resource
    Recent advances in the design of quasiaxisymmetric stellarator plasma configurations : 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. 2083-2094 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Strategies for the improvement of quasiaxisymmetric stellarator configurations are explored. Calculations of equilibrium flux surfaces for candidate configurations are also presented. One optimization strategy is found to generate configurations with improved neoclassical confinement, simpler coils with lower current density, and improved flux surface quality relative to previous designs. The flux surface calculations find significant differences in the extent of islands and stochastic regions between candidate configurations. (These calculations do not incorporate the predicted beneficial effects of perturbed bootstrap currents.) A method is demonstrated for removing low order islands from candidate configurations by relatively small modifications of the configuration. One configuration is identified as having particularly desirable properties for a proposed experiment. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1351826
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  • 10
    Electronic Resource
    Electronic Resource
    Chemical composition of Flourensia cernua at four growth stages (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Grass and forage science 51 (1996), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Tarbush (Flourensia cernua DC) is an abundant Chihuahuan Desert shrub but is used sparingly by livestock. Leaves were removed from forty tarbush plants harvested in each of 3 years during four growth stages: (1) early. (2) mid-point, (3) late and (4) curtailed growth (ten plants per growth stage each year). Plants were air dried and all leaves were removed. In vitro dry-matter (DM) disappearance was greater for the early growth stage than other stages (P〈005). The fibrous fraction increased with maturity, with neutral detergent fibre (NDF), acid detergent fibre (ADF) arid acid detergent lignin (ADL) contents all less for the early growth stage (P〈0 05) than other stages. The latter three growth stages did not differ in NDF or ADF content, but ADL content was lower for the mid-point growth stage than for the two later stages (P〈0–05). Calcium content increased with advancing season (P〈0–05), whereas phosphorus concentration exhibited an inverse pattern (P〈0–05). Nitrogen (N) content of tarbush was greatest in the early growth stage (P 〈0–05) and declined substantially thereafter. Soluble N content was greater and acid detergent insoluble N (ADIN) content was lower for early growth (P〈005) than other stages. Insoluble N concentration followed a pattern similar to N, declining with advancing season (P〈0–05). When expressed as a fraction of total N, insoluble N decreased and soluble N increased with maturity (P〈005). Condensed tannin concentration tended (P〈0–10) to increase with advancing season. Total phenolic content was lowest for early growth (P〈005), and did not differ among the other stages. Chemical analysis revealed tarbush to be relatively high in N concentration. Fibre fractions, ADIN, ADL and condensed tannins were ail generally low whereas total phenolic content of tarbush was quite high. Early use by livestock would be most advantageous in terms of nutrient availability (N, P and in vitro digestibility) and lowest total phenolic concentration. Year-to-year variability in chemical composition of tarbush appears to be substantial. It remains to be seen whether overriding intake deterrents would be beneficial to livestock, given the high phenolic concentration in tarbush. Tarbush has several characteristics that make it a suitable model for studying plant-animal interactions of desert shrubs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2494.1996.tb02078.x
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