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Статті в журналах з теми "HTS dynamo"

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Автор: Grafiati

Опубліковано: 10 грудня 2022

Оновлено: 28 січня 2023

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1

Hamilton, Kent, Ratu Mataira, Jianzhao Geng, Chris Bumby, Dale Carnegie, and Rod Badcock. "Practical Estimation of HTS Dynamo Losses." IEEE Transactions on Applied Superconductivity 30, no. 4 (June 2020): 1–5. http://dx.doi.org/10.1109/tasc.2020.2980830.

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2

Bumby, Chris W., Sinhoi Phang, Andres E. Pantoja, Zhenan Jiang, James G. Storey, Hae-Jin Sung, Minwon Park, and Rodney A. Badcock. "Frequency Dependent Behavior of a Dynamo-Type HTS Flux Pump." IEEE Transactions on Applied Superconductivity 27, no. 4 (June 2017): 1–5. http://dx.doi.org/10.1109/tasc.2016.2643498.

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3

Kalsi, S., R. A. Badcock, and K. A. Hamilton. "Coolant transfer coupling with integrated dynamo for rotor with HTS windings." IOP Conference Series: Materials Science and Engineering 756 (June 30, 2020): 012029. http://dx.doi.org/10.1088/1757-899x/756/1/012029.

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4

Storey, James G., Andres E. Pantoja, Zhenan Jiang, Rodney A. Badcock, and Chris W. Bumby. "Optimizing Rotor Speed and Geometry for an Externally Mounted HTS Dynamo." IEEE Transactions on Applied Superconductivity 29, no. 5 (August 2019): 1–5. http://dx.doi.org/10.1109/tasc.2019.2903038.

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5

Pantoja, Andres E., James G. Storey, Rodney A. Badcock, Zhenan Jiang, Sinhoi Phang, and Chris W. Bumby. "Output During Continuous Frequency Ramping of a Dynamo-Type HTS Flux Pump." IEEE Transactions on Applied Superconductivity 28, no. 3 (April 2018): 1–5. http://dx.doi.org/10.1109/tasc.2018.2793261.

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6

Hamilton, Kent, Andres E. Pantoja, James G. Storey, Zhenan Jiang, Rodney A. Badcock, and Chris W. Bumby. "Design and Performance of a “Squirrel-Cage” Dynamo-Type HTS Flux Pump." IEEE Transactions on Applied Superconductivity 28, no. 4 (June 2018): 1–5. http://dx.doi.org/10.1109/tasc.2018.2805161.

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7

Kalsi, S., R. A. Badcock, K. Hamilton, and J. G. Storey. "Homopolar superconducting AC machines, with HTS dynamo driven field coils, for aerospace applications." IOP Conference Series: Materials Science and Engineering 756 (June 30, 2020): 012028. http://dx.doi.org/10.1088/1757-899x/756/1/012028.

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8

Badcock, Rodney A., Sinhoi Phang, Andres E. Pantoja, Zhenan Jiang, James G. Storey, Hae-Jin Sung, Minwon Park, and Chris W. Bumby. "Impact of Magnet Geometry on Output of a Dynamo-Type HTS Flux Pump." IEEE Transactions on Applied Superconductivity 27, no. 4 (June 2017): 1–5. http://dx.doi.org/10.1109/tasc.2016.2636562.

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9

Ghabeli, Asef, Mark Ainslie, Enric Pardo, Loïc Quéval, and Ratu Mataira. "Modeling the charging process of a coil by an HTS dynamo-type flux pump." Superconductor Science and Technology 34, no. 8 (July 6, 2021): 084002. http://dx.doi.org/10.1088/1361-6668/ac0ccb.

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10

Pantoja, Andres E., Zhenan Jiang, Rodney A. Badcock, and Chris W. Bumby. "Impact of Stator Wire Width on Output of a Dynamo-Type HTS Flux Pump." IEEE Transactions on Applied Superconductivity 26, no. 8 (December 2016): 1–8. http://dx.doi.org/10.1109/tasc.2016.2598773.

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11

Storey, James G., Andres E. Pantoja, Zhenan Jiang, Kent Hamilton, Rodney A. Badcock, and Chris W. Bumby. "Impact of Annular Yoke Geometry on Performance of a Dynamo-Type HTS Flux Pump." IEEE Transactions on Applied Superconductivity 28, no. 3 (April 2018): 1–6. http://dx.doi.org/10.1109/tasc.2018.2797171.

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12

Nam, Gi-Dong, Hae-Jin Sung, Changhyun Kim, Junyeop Lee, Rodney A. Badcock, Zhenan Jiang, and Minwon Park. "Design and Performance Analysis of a Dynamo-Type HTS Flux Pump for a 10 kW Superconducting Generator." IEEE Transactions on Applied Superconductivity 30, no. 4 (June 2020): 1–5. http://dx.doi.org/10.1109/tasc.2020.2983362.

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13

Wen, Zezhao, Hongye Zhang, and Markus Mueller. "Sensitivity analysis and machine learning modelling for the output characteristics of rotary HTS flux pumps." Superconductor Science and Technology 34, no. 12 (November 12, 2021): 125019. http://dx.doi.org/10.1088/1361-6668/ac3463.

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Анотація:

Abstract High temperature superconducting (HTS) rotatory flux pump, or so called HTS dynamo, can output none-zero time-averaged DC voltage and charge the rest of the circuit if a closed loop has been formed. This type of flux pump is often employed together with HTS coils, where the HTS coils can potentially work in persistent current mode, and act like electromagnets with considerable magnetic field, having wide range of applications in industry. The output characteristics of HTS rotary flux pumps have been extensively explored through experiments and finite element method (FEM) simulations, yet the work on constructing statistical models as an alternative approach to capture key characteristics has not been studied and published. A 2D FEM program has been used to model the HTS rotatory flux pumps and evaluate the effects of different factors upon the output voltage through parameter sweeping and analysis of variance. Typical design considerations, including operation frequency, air gap, HTS tape width and remanent flux density have been investigated, in particular the bilateral effect of HTS tape width has been explained by looking at the averaged integration of the electric field over the tape. Based on the data obtained from various simulations, regression analysis has been conducted through a collection of machine learning methods and demonstrated that the output voltage of a rotary flux pump can be obtained promptly with satisfactory accuracy via Gaussian process regression, aiming to provide a novel approach for future research and powerful design tool for industrial applications using HTS rotary flux pump devices.

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14

Russo, Giacomo, and Antonio Morandi. "A Numerical Study on the Energization of the Field Coils of a Full-Size Wind Turbine with Different Types of Flux Pumps." Energies 15, no. 15 (July 26, 2022): 5392. http://dx.doi.org/10.3390/en15155392.

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Анотація:

High temperature superconductivity is emerging as a solution for lightweight, cost-effective and high-power wind generators. Current injection and maintainment/sustainment in the field winding are obtained by metal current leads which, due to persistent heat conduction and joule loss, are responsible for a large part of the total cryogenic heat load. Slip rings, which further reduce the overall performance and reliability of the system, are also required. In this paper we assess the viability of the HTS dynamo and the rectifier flux pumps for energizing the field coils of the EcoSwing 3.6 MW HTS wind generator. Both a “warm” solution, with the rectifier at room temperature, and a “cold” solution, in which the latter is integrated into the cryostat, are investigated with regard to the rectifier flux pump. A comparison with the actual, state-of-the-art, system of the EcoSwing machine is carried out in terms of the total required cooling power and the ability to charge the HTS field winding up to the rated current. It is found that the dynamo flux pump, beside avoiding the need of slip rings, allows the reduction in the required cooling by about 74% with respect to the conventional current-leads-based solution.

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15

Alaniz, Leela. "The Dynamo-Rhythm of Etienne Decroux and His Successors." Mime Journal 24, no. 1 (2014): 1–50. http://dx.doi.org/10.5642/mimejournal.20132401.02.

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16

Brandenburg, Axel, and Ilkka Tuominen. "The Solar Dynamo." International Astronomical Union Colloquium 130 (1991): 223–33. http://dx.doi.org/10.1017/s0252921100079665.

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Анотація:

AbstractThe traditionalαΩ-dynamo as a model for the solar cycle has been successful in explaining the butterfly diagram, phase relations between poloidal and toroidal field, and polar branch migration features. Observational and theoretical achievements in recent years have however shaken this picture. The current trend is towards dynamos operating in the overshoot region of the convection zone. Nevertheless, there are many open questions and a consistent picture has not been established. In this paper we compare recent approaches and discuss remaining problems.

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17

Weiss, Benjamin P., and Sonia M. Tikoo. "The lunar dynamo." Science 346, no. 6214 (December 4, 2014): 1246753. http://dx.doi.org/10.1126/science.1246753.

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Анотація:

The inductive generation of magnetic fields in fluid planetary interiors is known as the dynamo process. Although the Moon today has no global magnetic field, it has been known since the Apollo era that the lunar rocks and crust are magnetized. Until recently, it was unclear whether this magnetization was the product of a core dynamo or fields generated externally to the Moon. New laboratory and spacecraft measurements strongly indicate that much of this magnetization is the product of an ancient core dynamo. The dynamo field persisted from at least 4.25 to 3.56 billion years ago (Ga), with an intensity reaching that of the present Earth. The field then declined by at least an order of magnitude by ∼3.3 Ga. The mechanisms for sustaining such an intense and long-lived dynamo are uncertain but may include mechanical stirring by the mantle and core crystallization.

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18

Lorrain, P. "The Cowling 'limiting-points' proof of his anti-dynamo theorem." IEEE Transactions on Plasma Science 19, no. 5 (1991): 862–65. http://dx.doi.org/10.1109/27.108426.

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19

Schmitt, D. "The Solar Dynamo." Symposium - International Astronomical Union 157 (1993): 1–12. http://dx.doi.org/10.1017/s0074180900173784.

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Анотація:

The generation of the solar magnetic field is generally ascribed to dynamo processes in the convection zone. The dynamo effects, differential rotation (ω–effect) and helical turbulence (α–effect) are explained, and the basic properties of the mean–field dynamo equations are discussed in close comparison with the observed solar cycle.Especially the question of the seat of the dynamo is addressed. Problems of a dynamo in the convection zone proper could be magnetic buoyancy, the nearly strict observance of the polarity rules and the migration pattern of the magnetic fields which are difficult to understand in the light of recent studies of the field structure in the convection zone and by observations of the solar acoustic oscillations. To overcome some of these problems it has been suggested that the solar dynamo operates in the thin overshoot region at the base of the convection zone instead. Some aspects of such an interface dynamo are discussed. As an alternative to the turbulent α–effect a dynamic α-effect based on magnetostrophic waves driven by a magnetic buoyancy instability of a magnetic flux layer is introduced. Model calculations for both pictures, a convection zone and an interface dynamo, are presented which use the internal rotation of the sun as deduced from helioseismology. Solutions with solar cycle behaviour are only obtained if the magnetic flux is bounded in the lower convection zone and the α–effect is concentrated near the equator.Another aspect briefly addressed is the nonlinear saturation of the magnetic field. The necessity of the dynamic nature of the dynamo processes is emphasized, and different processes, e.g. magnetic buoyancy and α-quenching, are mentioned.

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20

Müller, U., and R. Stieglitz. "The Karlsruhe Dynamo Experiment." Nonlinear Processes in Geophysics 9, no. 3/4 (August 31, 2002): 165–70. http://dx.doi.org/10.5194/npg-9-165-2002.

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Abstract. It has been shown theoretically in the past that homogeneous dynamos may occur in electrically conducting fluids for various vortical velocity fields. Roberts (1972) investigated spatially periodic, infinitely extended fields of vortices which Busse (1978, 1992) confined to a finite cylindrical domain. Based on Busse's vortex arrangement a conceptual design for an experimental homogeneous dynamo has been developed and a test facility was setup at the Forschungszentrum Karlsruhe. The first experiments demonstrated that permanent dynamo action can be generated in a cylindrical container filled with liquid sodium in which by means of guide tubes counterrotating and countercurrent spiral vortices are established. The dynamo is self-exciting and the magnetic field saturates at a mean value for fixed super-critical flow rates. The instantaneous magnetic field fluctuates around this mean value by an order of about 5%. As predicted by theory the mode of the observed magnetic field is non-axisymmetric. In a series of experiments a phase- and a bifurcation diagram has been derived as a function of the spiral and axial flow rates.

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21

Stix, M. "III. The Solar Dynamo." Transactions of the International Astronomical Union 20, no. 1 (1988): 94–97. http://dx.doi.org/10.1017/s0251107x00007008.

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Traditionally the theory of the solar dynamo has been divided into two parts. The first, more difficult part, is the derivation of equations governing the mean magnetic field; the second, easier, is the solution of this equation, and the interpretation of the result in terms of observed solar magnetism. This report follows the traditional division.

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22

Hoyng, P. "Excitation of Dynamo Modes." Symposium - International Astronomical Union 138 (1990): 359–74. http://dx.doi.org/10.1017/s007418090004434x.

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Анотація:

After the very suggestive results of the early days, the theory of the solar dynamo has now entered a period of re-evaluation. It is clear that our initial expectations have been too high. I shall review some of the recent attempts to formulate nonlinear and stochastic mode excitation theoretically. We now have evidence from synoptic observations that the solar dynamo features many periods. Periods both shorter and longer than the fundamental 22 yr cycle have been claimed. The phase stability of any of these periods is uncertain. The phase memory of the 22 yr period may be as short as ~ 10 cycles, but could also be much longer. Linear mean field theories permit only one marginally stable mode; they predict one period with an infinitely long phase memory. Attempts to explain multiperiodicity and finite phase memory effects fall in two categories:(1). Nonlinear models. These feature a few nonlinearly coupled variables and may exhibit a multiperiodic or chaotic behaviour; (2). If the number of relevant variables is very high, then the dynamo behaves stochastically. It has been argued that this takes the form of stochastic excitation of many dynamo modes (overtones).

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23

Kurths, J., A. Brandenburg, U. Feudel, and W. Jansen. "Chaos in Nonlinear Dynamo Models." Symposium - International Astronomical Union 157 (1993): 83–89. http://dx.doi.org/10.1017/s0074180900173917.

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Анотація:

Two nonlinear dynamos have been analyzed by numerical means: 3D-simulation of the magneto-hydrodynamic equations and qualitative analysis of a simplified low-dimensional mean field model. It turns out that both are capable of deterministic chaos in a certain parameter range. As the basic tool the calculation of Lyapunov exponents has been used.

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24

ZABIELSKI, L., and A. J. MESTEL. "A double-helix laminar dynamo." Journal of Fluid Mechanics 573 (February 2007): 237–46. http://dx.doi.org/10.1017/s0022112006004174.

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Анотація:

It has recently been shown that laminar, pressure-driven flow of a conducting fluid in a helical pipe can generate a dynamo. Geometrical constraints have hitherto required a relatively small Reynolds number, and a much larger magnetic Reynolds number, Rm. Here, a configuration with two interwoven helical pipes is considered which is shown to drive a dynamo at a Reynolds number of a few hundred and Rm > 30. Various computer animations of the dynamo are available with the online version of the paper. It is found that hydrodynamic instabilities may inhibit the dynamo, but may also be regularized by it. It is also shown that a dynamo pump is possible, with flow down one pipe generating a field which drives flow in the second. Movies are available with the online version of the paper.

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25

Choudhuri, Arnab Rai. "Dynamo models of grand minima." Proceedings of the International Astronomical Union 7, S286 (October 2011): 350–59. http://dx.doi.org/10.1017/s174392131200508x.

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Анотація:

AbstractSince a universally accepted dynamo model of grand minima does not exist at the present time, we concentrate on the physical processes which may be behind the grand minima. After summarizing the relevant observational data, we make the point that, while the usual sources of irregularities of solar cycles may be sufficient to cause a grand minimum, the solar dynamo has to operate somewhat differently from the normal to bring the Sun out of the grand minimum. We then consider three possible sources of irregularities in the solar dynamo: (i) nonlinear effects; (ii) fluctuations in the poloidal field generation process; (iii) fluctuations in the meridional circulation. We conclude that (i) is unlikely to be the cause behind grand minima, but a combination of (ii) and (iii) may cause them. If fluctuations make the poloidal field fall much below the average or make the meridional circulation significantly weaker, then the Sun may be pushed into a grand minimum.

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26

Ferrier, R. C. "The DYNAMO Project: An Introduction." Hydrology and Earth System Sciences 2, no. 4 (December 31, 1998): 375–83. http://dx.doi.org/10.5194/hess-2-375-1998.

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Abstract. European concerns about the consequences of anthropogenic impacts on environmental quality have led to the establishment of various dynamic modelling approaches through which the consequences of impacts over time can be assessed. Similarly, throughout Europe, there has been extensive collection of regional data on "environmental capital" resulting in the production of wide area mapping of environmental quality (soils, land use etc). The aim of the DYNAMO was to integrate data and models, specifically; (1) to enhance the existing process based models to evaluate the impacts of multiple drivers of environmental change; (2) to evaluate these models at intensively studied (and manipulated) catchments and stands; (3) to scale up in time from observations collected over several years to predict the long term impacts over decades, and (4) to scale up in space from the individual site level to regional, National and European scale. The project aims to develop and enhance regional modelling approaches so that European scale impacts of acidic deposition, land use (forestry practices) and global change can be determined without compromising process level understanding of ecosystem function. The DYNAMO project contributes to the EU TERI (Terrestrial Ecosystems Research Initiative) framework of the Environment and Climate Programme of the European Commission.

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27

Brandenburg, A., D. Moss, M. Rieutord, G. Rüdiger та I. Tuominen. "αΛ-dynamos". International Astronomical Union Colloquium 130 (1991): 147–50. http://dx.doi.org/10.1017/s0252921100079550.

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Анотація:

Abstract In contrast to αω-dynamos, where the angular velocity is arbitrarily prescribed, we consider here αΛ-dynamos, for which the differential rotation and meridional circulation are solutions of the momentum equation. The non-diffusive parts of the Reynolds stress tensor are parameterized by the Λ-effect. In earlier investigations we have shown that the turbulent magnetic diffusivity has to be much smaller than the eddy viscosity, otherwise the dynamo is not oscillatory or else the contours of constant angular velocity are cylindrical, contrary to observations. In the present paper we investigate the effects of compressibility.

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28

Mighani, Saied, Huapei Wang, David L. Shuster, Cauȇ S. Borlina, Claire I. O. Nichols, and Benjamin P. Weiss. "The end of the lunar dynamo." Science Advances 6, no. 1 (January 2020): eaax0883. http://dx.doi.org/10.1126/sciadv.aax0883.

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Анотація:

Magnetic measurements of the lunar crust and Apollo samples indicate that the Moon generated a dynamo magnetic field lasting from at least 4.2 until <2.5 billion years (Ga) ago. However, it has been unclear when the dynamo ceased. Here, we report paleomagnetic and 40Ar/39Ar studies showing that two lunar breccias cooled in a near-zero magnetic field (<0.1 μT) at 0.44 ± 0.01 and 0.91 ± 0.11 Ga ago, respectively. Combined with previous paleointensity estimates, this indicates that the lunar dynamo likely ceased sometime between ~1.92 and ~0.80 Ga ago. The protracted lifetime of the lunar magnetic field indicates that the late dynamo was likely powered by crystallization of the lunar core.

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29

Brandenburg, A., R. L. Jennings, Å. Nordlund, M. Rieutord, R. F. Stein, and I. Tuominen. "Magnetic structures in a dynamo simulation." Journal of Fluid Mechanics 306 (January 10, 1996): 325–52. http://dx.doi.org/10.1017/s0022112096001322.

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Анотація:

We use three-dimensional simulations to study compressible convection in a rotating frame with magnetic fields and overshoot into surrounding stable layers. The, initially weak, magnetic field is amplified and maintained by dynamo action and becomes organized into flux tubes that are wrapped around vortex tubes. We also observe vortex buoyancy which causes upward flows in the cores of extended downdraughts. An analysis of the angles between various vector fields shows that there is a tendency for the magnetic field to be parallel or antiparallel to the vorticity vector, especially when the magnetic field is strong. The magnetic energy spectrum has a short inertial range with a slope compatible with k+1/3 during the early growth phase of the dynamo. During the saturated state the slope is compatible with k−1. A simple analysis based on various characteristic timescales and energy transfer rates highlights important qualitative ideas regarding the energy budget of hydromagnetic dynamos.

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30

Rüdiger, G., D. Elstner, and M. Schultz. "The Galactic Dynamo: Modes and Models." Symposium - International Astronomical Union 157 (1993): 321–31. http://dx.doi.org/10.1017/s0074180900174364.

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Анотація:

The hitherto known essentials of the present-day dynamo theory of the galactic magnetic fields are reported. The vertical stratification of the interstellar turbulence is exclusively considered as the source of the α-effect. New expressions for this tensorial effect and its quenching by the field are applied. Although its anisotropy and the influence of the halo easily yield the excitation of non-axisymmetric magnetic configurations of diverse equatorial symmetry, the galactic differential rotation finally leads to axisymmetric and quadrupolar solutions. The magnetic strength of the dynamo fields slightly exceeds the equipartition value while its angular momentum transport (into the intergalactic space) is very small.For increasingly steep vertical gradients of the turbulence intensity a saturation of the field strength is found since the eddy diffusivity grows with the α-effect. Only beyond the maximum of the field the equatorial symmetry changes to an equatorial antisymmetry,i.e.to dipolar solutions.In order to produce the observed values of the pitch angles one has only to choose correlation times of the turbulence slightly exceeding the usually accepted 107yrs.

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31

Krause, F. "Stellar Dynamos." International Astronomical Union Colloquium 137 (1993): 578–90. http://dx.doi.org/10.1017/s0252921100018509.

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Анотація:

AbstractEnergy is transported from the central regions of a star to its surface. Generally this transport is in certain layers carried on by convective motions. Because of the structure, which these motions have due to the influence of the overall rotation, the star becomes electromagnetically unstable, i.e. a large magnetic field grows from small seed fields as a result of the dynamo process. The internal structure, especially the symmetries of a star, will be, at least to some extend, reflected by the spatial structure and the time behaviour of the excited magnetic field. In this sense observations of the magnetic field on a surface of a star and the related activity phenomena can provide insight in the internal structure of the star, since characteristic parameters like thickness of the convection zone, mixing length, turnover time, profile of the differential rotation, etc. strongly influence the dynamo process.The actual magnetic field of a star is a product of a nonlinear process. Models elaborated on the kinematical (i.e. linear) level provide insight in the excitation conditions and the linear field modes. The marginal mode, i.e. the mode which is easiest to excite, reflects properties of the nonlinear solution in case the system operates not far from the margin to the dynamo unstable region. Here the solutions show symmetries with respect to the axis of rotation and the equatorial plane, properties which are, for example, to a large extend fulfilled for the solar average magnetic field. For systems operating far from this margin irregular or even chaotic behaviour has to be expected. From observations there is a strong indication that these theoretical possibilities find their realizations within the sample of late-type stars.

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32

Tuominen, I., G. Rüdiger, and A. Brandenburg. "Torsional Oscillations and the Solar Dynamo Regime." Symposium - International Astronomical Union 138 (1990): 387–90. http://dx.doi.org/10.1017/s0074180900044387.

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Анотація:

We discuss the observational results of cyclic variations of solar rotation and how these can be used as a means of probing the solar dynamo. We shortly describe two examples of dynamo models where the α-effect has been modified, and compare the resulting flows to the observations.

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33

KLEIDIS, KOSTAS, APOSTOLOS KUIROUKIDIS, DEMETRIOS PAPADOPOULOS, and LOUKAS VLAHOS. "DYNAMO EFFECTS IN MAGNETIZED IDEAL PLASMA COSMOLOGIES." International Journal of Modern Physics A 23, no. 11 (April 30, 2008): 1697–710. http://dx.doi.org/10.1142/s0217751x08039542.

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Анотація:

The excitation of cosmological perturbations in an anisotropic cosmological model and in the presence of a homogeneous magnetic field has been studied, using the ideal magnetohydrodynamic (MHD) equations. In this case, the system of partial differential equations which governs the evolution of the magnetized cosmological perturbations can be solved analytically. Our results verify that fast-magnetosonic modes propagating normal to the magnetic field, are excited. But, what is most important, is that, at late times, the magnetic-induction contrast(δB/B) grows, resulting in the enhancement of the ambient magnetic field. This process can be particularly favored by condensations, formed within the plasma fluid due to gravitational instabilities.

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34

Borlina, Cauê S., Benjamin P. Weiss, Eduardo A. Lima, Fengzai Tang, Richard J. M. Taylor, Joshua F. Einsle, Richard J. Harrison, et al. "Reevaluating the evidence for a Hadean-Eoarchean dynamo." Science Advances 6, no. 15 (April 2020): eaav9634. http://dx.doi.org/10.1126/sciadv.aav9634.

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The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown.

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35

Moffatt, H. K., and M. R. E. Proctor. "Topological constraints associated with fast dynamo action." Journal of Fluid Mechanics 154 (May 1985): 493–507. http://dx.doi.org/10.1017/s002211208500163x.

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The conjecture of Vainshtein & Zel'dovich (1972) concerning the existence of a fast dynamo (i.e. one whose growth rate is independent of magnetic diffusivity η in the limit η → 0) is discussed with particular reference to (i) the stretch–twist–fold cycle which can double the strength of a magnetic flux tube, and (ii) the space-periodic Beltrami flow of maximal helicity, which has been shown to be capable of space-periodic dynamo action with the same period as the velocity field, by Arnold & Korkina (1983) and by Galloway & Frisch (1984). The topological constraint associated with conservation of magnetic helicity is shown to preclude fast dynamo action unless the scale of the magnetic field is almost everywhere of order η½ as η → 0; in this case, the field structure is severely singular in the limit. A steady incompressible velocity field, quadratic in the space variables, is shown to mimic the action of the stretch–twist–fold cycle, and is proposed as a plausible candidate for fast dynamo action.

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36

Weiss, Nigel O. "Solar and Stellar Dynamos." Proceedings of the International Astronomical Union 6, S271 (June 2010): 247–60. http://dx.doi.org/10.1017/s1743921311017674.

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AbstractRecords of the solar magnetic field extend back for millennia, and its surface properties have been observed for centuries, while helioseismology has recently revealed the Sun's internal rotation and the presence of a tachocline. Dynamo theory has developed to explain these observations, first with idealized models based on mean-field electrodynamics and, more recently, by direct numerical simulation, notably with the ASH code at Boulder. These results, which suggest that cyclic activity relies on the presence of the tachocline, and that its modulation is chaotic (rather than stochastic), will be critically reviewed. Similar theoretical approaches have been followed in order to explain the magnetic properties of other main-sequence stars, whose fields can be mapped by Zeeman-Doppler imaging. Of particular interest is the behaviour of fully convective, low-mass stars, which lack any tachocline but are nevertheless extremely active.

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37

Oakes, Tim. "Building a Southern Dynamo: Guizhou and State Power." China Quarterly 178 (June 2004): 467–87. http://dx.doi.org/10.1017/s0305741004000268.

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Guizhou's west to east electricity transfer project is a major energy infrastructure development project associated with the campaign to Open Up the West. In terms of state investments, the project has been the major feature of the campaign in Guizhou. It indicates the intensification of, rather than departure from, a long-term pattern of western primary resource exploitation for the purposes of eastern development. Guizhou's experience in the campaign to Open Up the West has mostly been about “big development,” and the campaign may even represent a new stage in the province's long history of internal colonization. In broader terms, the west to east electricity transfer project is indicative of the campaign's agenda to recentralize state political and economic control away from provinces which have gained considerable autonomy during the reform era. Along with the burst of infrastructure, the implications for Guizhou appear to be a continuation of uneven patterns of exchange between coast and interior. Tied increasingly to its role as net supplier of power to Guangdong, Guizhou could face fresh challenges in diversifying its economy sufficiently to withstand the impacts of China's World Trade Organization accession.

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38

Krause, F., та G. Scholz. "Does 𝓿 Cep indicate a non-axisymmetric dynamo?" International Astronomical Union Colloquium 90 (1986): 51–54. http://dx.doi.org/10.1017/s0252921100091211.

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AbstractAccording to observations of Scholz and Gerth the super-giant 𝓿 Cep has a magnetic field with a maximum field strength up to 2500 Gauss. This field shows a period of about 5 years. It is unplausible that this magnetic field is a relic since 𝓿 Cep was formed by expansion of a B-star. We claim here that 𝓿 Cep represents a dynamo exciting a magnetic field which in the average strongly deviates from symmetry about the rotation axis.

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39

Weber, Maria A. "Dynamo Processes Constrained by Solar and Stellar Observations." Proceedings of the International Astronomical Union 13, S340 (February 2018): 275–80. http://dx.doi.org/10.1017/s1743921318001424.

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AbstractOur understanding of stellar dynamos has largely been driven by the phenomena we have observed of our own Sun. Yet, as we amass longer-term datasets for an increasing number of stars, it is clear that there is a wide variety of stellar behavior. Here we briefly review observed trends that place key constraints on the fundamental dynamo operation of solar-type stars to fully convective M dwarfs, including: starspot and sunspot patterns, various magnetism-rotation correlations, and mean field flows such as differential rotation and meridional circulation. We also comment on the current insight that simulations of dynamo action and flux emergence lend to our working knowledge of stellar dynamo theory. While the growing landscape of both observations and simulations of stellar magnetic activity work in tandem to decipher dynamo action, there are still many puzzles that we have yet to fully understand.

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40

MOROZ, IRENE M. "THE MALKUS–ROBBINS DYNAMO WITH A LINEAR SERIES MOTOR." International Journal of Bifurcation and Chaos 13, no. 01 (January 2003): 147–61. http://dx.doi.org/10.1142/s0218127403006431.

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Hide [1997] has introduced a number of different nonlinear models to describe the behavior of n-coupled self-exciting Faraday disk homopolar dynamos. The hierarchy of dynamos based upon the Hide et al. [1996] study has already received much attention in the literature (see [Moroz, 2001] for a review). In this paper we focus upon the remaining dynamo, namely Case 3 of [Hide, 1997] for the particular limit in which the Malkus–Robbins dynamo [Malkus, 1972; Robbins, 1997] obtains, but now modified by the presence of a linear series motor. We compare and contrast the linear and the nonlinear behaviors of the two types of dynamo.

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41

Kuzanyan, Kirill M. "Solar and Stellar Dynamo Waves Under Asymptotic Investigation." International Astronomical Union Colloquium 167 (1998): 415–18. http://dx.doi.org/10.1017/s0252921100048028.

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AbstractThe main magnetic activity of the Sun can be visualised by Maunder butterfly diagrams which represent the spatio-temporal distribution of sunspots. Besides sunspots there are other tracers of magnetic activity, like filaments and active regions, which are observable over a wider latitudinal range of the Sun. Both these phenomena allow one to consider a complete picture of solar magnetic activity, which should be explained in the framework of one relatively simple model.A kinematic αѡ-dynamo model of the magnetic field’s generation in a thin convection shell with nonuniform helicity for large dynamo numbers is considered in the framework of Parker’s migratory dynamo. The obtained asymptotic solution of equations governing the magnetic field has a form of a modulated travelling dynamo wave. This wave propagates over the most latitudes of the solar hemisphere equatorwards, and the amplitude of the magnetic field first increases and then decreases with the propagation. Over the subpolar latitudes the dynamo wave reverses, there the dynamo wave propagates polewards and decays with latitude. Butterfly diagrams are plotted and analyzed.There is an attractive opportunity to develop a more quantitatively precise model taking into account helioseismological data on differential rotation and fitting the solar observational data on the magnetic field and turbulence, analyzing the helicity and the phase shift between toroidal and poloidal components of the field.

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42

Giesecke, André, Frank Stefani, Thomas Gundrum, Gunter Gerbeth, Caroline Nore, and Jacques Léorat. "Experimental realization of dynamo action: present status and prospects." Proceedings of the International Astronomical Union 8, S294 (August 2012): 411–16. http://dx.doi.org/10.1017/s1743921313002846.

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AbstractIn the last decades, the experimental study of dynamo action has made great progress. However, after the dynamo experiments in Karlsruhe and Riga, the von-Kármán-Sodium (VKS) dynamo is only the third facility that has been able to demonstrate fluid flow driven self-generation of magnetic fields in a laboratory experiment. Further progress in the experimental examination of dynamo action is expected from the planned precession driven dynamo experiment that will be designed in the framework of the liquid sodium facility DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies).In this paper, we briefly present numerical models of the VKS dynamo that demonstrate the close relation between the axisymmetric field observed in that experiment and the soft iron material used for the flow driving impellers. We further show recent results of preparatory water experiments and design studies related to the precession dynamo and delineate the scientific prospects for the final set-up.

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43

Proctor, Michael R. E., and David W. Hughes. "Competing kinematic dynamo mechanisms in rotating convection with shear." Proceedings of the International Astronomical Union 6, S271 (June 2010): 239–46. http://dx.doi.org/10.1017/s1743921311017662.

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AbstractFollowing earlier work by Hughes & Proctor (2009) on the role of velocity shear in convectively driven dynamos, we present preliminary results on the nature of dynamo action due to modified flows derived by filtration from the full convective flow. The results suggest that filtering the flow fields has surprisingly little effect on the dynamo growth rates.

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44

Christensen, Ulrich R., Julien Aubert, and Peter Olson. "Convection-driven planetary dynamos." Proceedings of the International Astronomical Union 2, S239 (August 2006): 188–95. http://dx.doi.org/10.1017/s1743921307000403.

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AbstractNumerical simulations of convection-driven dynamos in rotating spherical shells are employed to better understand the observed strength and geometry of planetary magnetic fields. The model computations cannot be performed for realistic values of several of the control parameters. By varying parameters within the accessible range, it is possible to derive scaling laws for the magnetic field strength and the flow velocity in the dynamo region and for the dipole moment. Our scaling laws suggest that, even though diffusivities are far too large in the models, diffusive processes do not play an important role, just as in planetary cores. Extrapolating the scaling laws to planetary values of the control parameters leads to reasonable predictions for the field strength in the dynamo region and fits the observed dipole moments decently, in particular in the cases of Earth and Jupiter. For Mercury, which does not fit well when applying the scaling laws in a straightforward way, a model is proposed in which the upper part of the fluid core is stably stratified and the dynamo operates only in its deep regions. The time-varying dynamo field must diffuse through the stable region and is attenuated by the skin effect. The model explains why Mercury has a very weak but probably dipole-dominated magnetic field.

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45

Jouve, Laurène, and Rohit Kumar. "On the connections between solar and stellar dynamo models." Proceedings of the International Astronomical Union 12, S328 (October 2016): 12–21. http://dx.doi.org/10.1017/s1743921317004124.

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AbstractWe here discuss the various dynamo models which have been designed to explain the generation and evolution of large-scale magnetic fields in stars. We focus on the models that have been applied to the Sun and can be tested for other solar-type stars now that modern observational techniques provide us with detailed stellar magnetic field observations. Mean-field flux-transport dynamo models have been developed for decades to explain the solar cycle and applications to more rapidly-rotating stars are discussed. Tremendous recent progress has been made on 3D global convective dynamo models. They do not however for now produce regular flux emergence that could be responsible for surface active regions and questions about the role of these active regions in the dynamo mechanism are still difficult to address with such models. We finally discuss 3D kinematic dynamo models which could constitute a promising combined approach, in which data assimilation could be applied.

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46

Rädler, K. H., M. Rheinhardt, E. Apstein, and H. Fuchs. "On the mean-field theory of the Karlsruhe Dynamo Experiment." Nonlinear Processes in Geophysics 9, no. 3/4 (August 31, 2002): 171–87. http://dx.doi.org/10.5194/npg-9-171-2002.

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Abstract. In the Forschungszentrum Karlsruhe an experiment has been constructed which demonstrates a homogeneous dynamo as is expected to exist in the Earth's interior. This experiment is discussed within the framework of mean-field dynamo theory. The main predictions of this theory are explained and compared with the experimental results. Key words. Dynamo, geodynamo, dynamo experiment, mean-field dynamo theory, a-effect

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47

FEUDEL, ULRIKE, WOLFGANG JANSEN, and JÜRGEN KURTHS. "TORI AND CHAOS IN A NONLINEAR DYNAMO MODEL FOR SOLAR ACTIVITY." International Journal of Bifurcation and Chaos 03, no. 01 (February 1993): 131–38. http://dx.doi.org/10.1142/s021812749300009x.

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A nonlinear dynamo model for solar activity which includes the feedback of the helicity upon the mean magnetic field has been investigated. The qualitative behavior of a seven-dimensional system of ordinary differential equations obtained by truncation of that model has been studied numerically. It has been compared with results from a sixth order system derived from the seventh order system by a special polar coordinate transformation. Depending on characteristic parameters, the seven-dimensional model exhibits periodic, quasiperiodic (on T2 and T3) and chaotic behavior where a route to chaos via the transition T2⇒T3⇒T2⇒ chaos has been found to be typical. In contrast to that, no chaotic state occurs in the reduced system due to a nonregularity of the coordinate transformation.

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48

Chapman, P. B., J. N. Glover, and A. I. Mees. "The dynamics of the Rikitake dynamo from the stiff limit." Mathematical Proceedings of the Cambridge Philosophical Society 108, no. 1 (July 1990): 171–91. http://dx.doi.org/10.1017/s0305004100069036.

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The Rikitake two-disc system [10] has been proposed as a model of the Earth's magnetic dipole. Numerical integration of the system by Rikitake[10] and Allan [1] showed the phenomenon of polarity reversal which is seen in terrestrial paleomagnetic data [6]. Reversals in the simulations occurred at irregular and apparently unpredictable time intervals, in accord with the capricious character of the real data, though the agreement was qualitative rather than quantitative.

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49

Vidal, Jérémie, and David Cébron. "Kinematic dynamos in triaxial ellipsoids." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, no. 2252 (August 2021): 20210252. http://dx.doi.org/10.1098/rspa.2021.0252.

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Planetary magnetic fields are generated by motions of electrically conducting fluids in their interiors. The dynamo problem has thus received much attention in spherical geometries, even though planetary bodies are non-spherical. To go beyond the spherical assumption, we develop an algorithm that exploits a fully spectral description of the magnetic field in triaxial ellipsoids to solve the induction equation with local boundary conditions (i.e. pseudo-vacuum or perfectly conducting boundaries). We use the method to compute the free-decay magnetic modes and to solve the kinematic dynamo problem for prescribed flows. The new method is thoroughly compared with analytical solutions and standard finite-element computations, which are also used to model an insulating exterior. We obtain dynamo magnetic fields at low magnetic Reynolds numbers in ellipsoids, which could be used as simple benchmarks for future dynamo studies in such geometries. We finally discuss how the magnetic boundary conditions can modify the dynamo onset, showing that a perfectly conducting boundary can strongly weaken dynamo action, whereas pseudo-vacuum and insulating boundaries often give similar results.

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50

Teplitskaya, R. B., and V. G. Skochilov. "Does a Common Dynamo Mechanism Exist for Lower Main Sequence Stars?" Symposium - International Astronomical Union 138 (1990): 455–59. http://dx.doi.org/10.1017/s0074180900044466.

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Based on an extended list of lower main sequence stars from Rutten (1987), the relation between chromospheric activity and Rossby number has been revised. The increased statistics changes the shape of the curve as compared with that of Noyes et al. (1984). The saturation at small Rossby numbers has disappeared. The dependence on Rossby number in the range of very large Rossby numbers has weakened. The standard deviation of the activity indices from the mean curve is about 40%. This scatter of individual stars is not due to differences in the spectral type or age of the stars.

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