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  • Books
  • Articles  (16)
  • fusion reactors  (8)
  • variogram  (8)
  • 2020-2020
  • 1980-1984  (16)
  • 1950-1954
  • Geosciences  (8)
  • Energy, Environment Protection, Nuclear Power Engineering  (8)
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  • Books
  • Articles  (16)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 2 (1982), S. 207-224 
    ISSN: 1572-9591
    Keywords: tokamaks ; fusion reactors ; plasma physics ; ignition ; transport ; performance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Studies have been performed to explore various plasma burn scenarios for a tokamak test reactor which could follow the next generation of large tokamak experiments. Tradeoffs between an ignited burning plasma and a sub-ignited driven plasma are examined in terms of device size and performance as a fusion engineering test facility. It is found that plasma performance levels, measured by ignition margin, amplification factorQ, and fusion power output, increase with device size, more optimistic transport scaling laws, lower magnetic field ripple, and higherΒ. The performance of a generally low stress (B 0=4 T) reference device, with major radiusR=4.5 m and minor radiusa=1.3 m in a D-shaped (κ=1.6) plasma has been evaluated over a wide range of operating parameters. In particular, a moderate fusion power output of 300 MW is obtained, the driven plasma havingQ≅ 10, an edge ripple of 1%, and a density ranging between 1.0 and 1.5×1014 cm−3. The same device operated at a higher general level of stress (B 0=5.3 T) is predicted to achieve ignition, but is not required for the mission of an engineering test facility and would entail greater technical risk.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 3 (1983), S. 217-229 
    ISSN: 1572-9591
    Keywords: tokamak ; fusion reactors ; tokamak scaling ; ignition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A study of the interaction between the physics of ignition and the engineering constraints in the design of compact, high-field tokamak ignition demonstration devices is presented. The studies investigate the effects the various electron and ion thermal diffusivities, which result from the many tokamak scaling laws, have on the design parameters of an ignition device and show the feasibility of building and igniting a compact tokamak (R 〈 1m). The relevant machine technology is discussed.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 2 (1982), S. 197-205 
    ISSN: 1572-9591
    Keywords: fusion reactors ; tritium breeding ; semicatalyzed deuterium ; tokamak
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Nontritium-breeding D-T reactors have decisive advantages in minimum size, unit cost, variety of applications, and ease of heat removal over reactors using any other fusion cycle, and significant advantages in environmental and safety characteristics over breeding D-T reactors. Considerations of relative energy production demonstrate that the most favorable source of tritium for a widely deployed system of nontritium-breeding D-T reactors is the very large (∼10 GW thermal) semicatalyzed-deuterium (SCD), or sub-SCD reactor, where none of the escaping3He (〉 95%) or tritium (〈 25%) is reinjected for burn-up. Feasibility of the ignited SCD tokamak reactor requires spatially averaged betas of 15 to 20% with a magnetic field at the TF coils of 12–13 T.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 3 (1983), S. 283-302 
    ISSN: 1572-9591
    Keywords: fusion reactors ; inertial confinement ; thermonuclear reactor ; Monte Carlo method ; breeding ratio ; neutron sources ; neutron flux
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The neutronics and photonics performance of a pellet with a small DT core spark trigger, surrounded by a large volume of D to enable tritium and He-3 breeding, is examined. The response to a 70% DD and 30% DT composite neutron spectrum is calculated using either W, Be, or Pb as structural materials at core density radius products ranging from 9.42 to 94.2 kg/m2. At a core density-product of 94.2, the DT neutron source leads to an excess particle multiplication of 0.43 neutrons per source neutron. The percentage of energy leakage from the pellet in the form of escaped neutrons is 42.3% of the source energy for the DT source, and 28.8% for the DD source. The gamma-ray energy percentage deposited in the pellet is 26.7% for the DT source and 106.6% for the DD source. For the pellet with the composite source, the energy multiplication factor is 1.27. Thus the large DD contribution to the composite neutron source results in the pellet performing many of the functions normally reserved for the blanket such as spectral softening, breeding, and neutron and energy multiplication. The neutron energy leakage is 38.4% of the source energy for the composite source. It is estimated that the neutron energy leakage amounts to 10% of the fusion energy, compared with 70% as neutron energy in a DT pellet. These results are significantly different from those encountered in conventional DT inertial confinement designs, and thus lower tritium inventories, higher power densities, reduced radiation damage, and materials activation of the reactor coolant and structure may be achievable.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 14 (1982), S. 629-644 
    ISSN: 1573-8868
    Keywords: variogram ; kriging ; interpolation ; contouring ; inverse distance weighting ; geochemical gradient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Four variogram models for regional groundwater geochemical data are presented. These models were developed from an empirical study of the sample variograms for more than 10 elements in groundwaters from two geologic regions in the Plainview quandrangle, Texas. A procedure is given for the estimation of the variogram in the isotropic and anisotropic case. The variograms were found useful for quantifying the differences in spatial variability for elements within a geologic unit and for elements in different geologic units. Additionally, the variogram analysis enables assessment of the assumption of statistical independence of regional samples which is commonly used in many statistical procedures. The estimated variograms are used in computation of kriged estimates for the Plainview quadrangle data. The results indicate that an inverse distance weighting model was superior for prediction than simple kriging with the particular variograms used.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 14 (1982), S. 77-85 
    ISSN: 1573-8868
    Keywords: Geostatistics ; variogram ; polygonal function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The application of regionalized variables requires the estimation of the variogram function and the evaluation of its integral. By representing the variogram by a general polygonal function the requisite integrals may be easily computed by a closed form representation of simple integrals. This paper provides the integration formulas for two-dimensional variogram functions whose domain is represented as a finite collection of rectangles. The integration formulas essential for a fully developed polygonal approach to an extensive statistical evaluation of geostatistical quantities are presented.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 15 (1983), S. 553-564 
    ISSN: 1573-8868
    Keywords: variogram ; estimation ; conditionally positive semidefinite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Estimation of linear combinations is accomplished by using the observed (available) data. Accordingly, to require the negative of a modeled variogram function to be positive definite for all possible data combinations is unnecessary when only the observed data are used in estimation. The requirement that the negative of a variogram model be conditionally positive semidefinite is then relaxed to apply at the observed spatial locations only. In this setting a simple, yet crude, sufficient condition is developed to ensure that a variogram model will yield nonnegative variances for the available data. It is seen that the condition is independent of the dimensionality of the data and applies to both isotropic and anisotropic models. An example of the application of the condition is also presented. The condition is harder to satisfy as the amount of data increases and must be adjusted as the variogram changes to accommodate new data.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 12 (1980), S. 115-125 
    ISSN: 1573-8868
    Keywords: Geostatistics ; kriging ; robust estimation ; variogram
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract It is a matter of common experience that ore values often do not follow the normal (or lognormal) distributions assumed for them, but, instead, follow some other heavier-tailed distribution. In this paper we discuss the robust estimation of the variogram when the distribution is normal-like in the central region but heavier than normal in the tails. It is shown that the use of a fourth-root transformation with or without the use of M-estimation yields stable robust estimates of the variogram.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 12 (1980), S. 577-588 
    ISSN: 1573-8868
    Keywords: variogram ; geostatistics ; estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract The application of regionalized variables requires the estimation of the variogram function and the evaluation of its integral. By representing the variogram by a polygonal function the integral may be easily approximated by closed form representations of polygonal integrals. This approach provides a basis for more extensive statistical evaluation not evident in existing approximation methods. This paper provides the closed form representations for two-dimensional variogram functions whose domain is represented by a finite collection of rectangles.
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  • 10
    ISSN: 1573-8868
    Keywords: geostatistics ; variogram ; outliers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Variograms for gold and lead values from the Loraine and Prieska mines, respectively, indicate that data outliers can seriously distort and/or mask the real variogram patterns. Studies show that this problem is best overcome for these mines by logarithmic transformation of the data, and/or a suitable screening out of such outliers, and/or more robust variogram estimation procedures; the benefits are particularly significant when the basic data is limited.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 16 (1984), S. 809-822 
    ISSN: 1573-8868
    Keywords: variogram ; robustness ; kriging ; conditioning number
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Current ideas of robustness in geostatistics concentrate upon estimation of the experimental variogram. However, predictive algorithms can be very sensitive to small perturbations in data or in the variogram model as well. To quantify this notion of robustness, nearness of variogram models is defined. Closeness of two variogram models is reflected in the sensitivity of their corresponding kriging estimators. The condition number of kriging matrices is shown to play a central role. Various examples are given. The ideas are used to analyze more complex universal kriging systems.
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 16 (1984), S. 407-421 
    ISSN: 1573-8868
    Keywords: variogram ; geostatistics ; positive-definite ; Bochner's theorem ; Hankel transforms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract A method based on Bochner's theorem is described for demonstrating the positive-definiteness of variogram models and for generating classes of valid variogram functions.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 1 (1981), S. 367-380 
    ISSN: 1572-9591
    Keywords: fusion reactors ; tandem mirror ; transport theory ; Monte Carlo method ; sampling ; mathematical models ; radiation transport ; neutron transport ; shielding ; magnets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A neutronics analysis using the Monte Carlo method is carried out for the end-plug penetration and magnet system of a tandem mirror fusion reactor. Detailed penetration and the magnets' three-dimensional configurations are modeled. A method of position dependent angular source biasing is developed to adequately sample the DT fusion source in the central cell region and obtain flux contributions at the penetration components. To assure cryogenic stability, the barrier cylindrical solenoid is identified as needing substantial shielding of about 1 m of a steel-lead-boron-carbide-water mixture. Heating rates there would require a thermal-hydraulic design similar to that in the central cell blanket region. The transition coils, however, need a minimal 0.2 m thickness shield. The leakage neutron flux at the direct converters is estimated at 1.3×1015 n/(m2·s), two orders of magnitude lower than that reported at the neutral beam injectors for tokamaks around 1017 n/(m2·s) for a 1 MW/m2 14 MeV neutron wall loading. This result is obtained through a coupling between the nuclear and plasma physics designs in which hydrogen ions rather than deuterium atoms are used for energy injection at the end plug, to avoid creating a neutron source there. This lower and controllable radiation leakage problem is perceived as a potential major advantage of tandem mirrors compared to tokamaks and laser reactor systems.
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 1 (1981), S. 381-386 
    ISSN: 1572-9591
    Keywords: fusion reactors ; ELMO bumpy torus ; D-burning advanced fuels ; ratio of particle to energy confinement time ; ash buildup ; neoclassical transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Results of a point model calculation for advanced fuel (cat. D and D3He) EBT reactors are used to determine some of the limitations on the ratio of ion particle to energy confinement timeξ. The greater fraction of charged fusion products produced in the advanced fuel reactions and the greater fraction of their energy radiated cause the effect ofξ on ash buildup to be a factor of 4 greater for the advanced fuels than that of DT fuel. Hence it is found thatξ〈5 for steady state ignited advanced fuel EBT reactors, whereasξ ⩽22 is the restriction for DT fueled EBT reactors. A survey ofξ for neoclassical bumpy torus ions reveals that in the plateau regime,ξ〈5 appears possible but is critically dependent on the nature of the electric field.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 3 (1983), S. 13-24 
    ISSN: 1572-9591
    Keywords: fusion reactors ; current drive ; neutral beams ; tokamak ; internal transformer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A large improvement in efficiency of current drive in a tokamak can be obtained using neutral beam injection to drive the current in a plasma which has low density and high resistivity. The current established under such conditions acts as the primary of a transformer to drive current in an ignited high-density plasma. In the context of a model of plasma confinement and fusion reactor costs, it is shown that such transformer action has substantial advantages over strict steady-state current drive. It is also shown that cycling plasma density and fusion power is essential for effective operation of an internal transformer cycle. Fusion power loading must be periodically reduced for intervals whose duration is comparable to the maximum of the particle confinement and thermal inertia time scales for plasma fueling and heating. The design of neutron absorption blankets which can tolerate reduced power loading for such short intervals is identified as a critical problem in the design of fusion power reactors.
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 2 (1982), S. 173-178 
    ISSN: 1572-9591
    Keywords: neutron activation ; neutral beam injectors ; fusion reactors ; doses rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The dose equivalent rates outside the Engineering Test Facility neutral beam injector shield from the induced radioactivity have been calculated for the reactor operating at 1140 MW for 1, 30, and 365 days. The dose rates at one day after shutdown are large even after one day of operation. Depending on the location and operating time, cooling times from 30 days to ∼ 5 years are required before the dose rates are sufficiently low to allow routine maintenance work in the vicinity of the NBI shield.
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