Asymmetric magnetic flux generation, <i>m</i>=1 activity, and edge phenomena on a reversed-field pinch

Howell, Robert B.; Ingraham, J. C.; Wurden, G. A.; Weber, P.; Buchenauer, C.J.

doi:10.1063/1.866198

Cited by 49 publications

(34 citation statements)

References 24 publications

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“…This can be explained by the above scenario that the m=O mode grows as a result of the nonlinear coupling of the m=l modes, and agrees well with the recent experimental observation. 19 > The dashed lines in the figures for W and F denote the simulation results for the case in which the perturbations (m; n)=F(O; 0) are excluded at time t=lOOrA. In this case the time development of the system is governed solely by the dissipation process, no relaxation process coming into play.…”

Section: Simulation Study Of the Nonlinear Dynamics In Rfpmentioning

confidence: 97%

Simulation Study of Self-Organization and Self-Relaxation Processes in Plasma

Horiuchi¹,

Kusano²,

Watanabe

et al. 1989

Prog. Theor. Phys. Suppl.

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Recent progress in super-computers has opened a new tool for the study of nonlinear dynamics in plasmas. This paper reviews the recent computer simulation studies for the self-organization and self-relaxation processes in MHD plasmas carried out by the Hiroshima group. Taylor's conjecture for the selective dissipation of magnetic energy keeping the total magnetic helicity constant is confirmed and the mechanisms for formation and maintenance of the reversed field pinch configuration are explained in terms of the self-relaxation of the plasma due to a driven magnetic reconnection triggered by ideal MHD helical kink unstable modes and their nonlinear couplings. § 1. IntroductionThe second law of thermodynamics predicts that the entropy of an isolated system increases monotonically_ At a glance, this law appears to imply that any structures in universe continuously decay and that the entire universe will eventually evolve to a state of complete randomness or uniformity. In our universe, however, a wide variety of structures does exist and continues to develop, as can be seen most clearly in the biological system_ 1 J Such a spontaneous generation and maintenance of structures is called a self organization process and can be widely observed in non-biological systems in nature. Formation of an ordered structure in fluids such as the Benard cell or a coherent oscillation reaction as the Belousov-Zhabotinsky reaction are the well-known examples.2l Recent progress in plasma physics has revealed that a plasma exhibits many such self-organization processes. In this paper, we present a review of the recent research on nonlinear dynamics associated with the self-organization processes in plasmas. Particular emphasis will be placed on the results of computer simulations that have made an important contribution to progress in this research.Self-organization in nature has attracted not only the poetic physicists, but also the nuclear fusion scientists who have been trying to find a magnetic field configuration, which can confine a high-temperature plasma in a stable and steady state. Since instabilities and resistive diffusions will disturb or modify the magnetic at

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Section: Simulation Study Of the Nonlinear Dynamics In Rfpmentioning

confidence: 97%

Simulation Study of Self-Organization and Self-Relaxation Processes in Plasma

Horiuchi¹,

Kusano²,

Watanabe

et al. 1989

Prog. Theor. Phys. Suppl.

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“…Magnetic fluctuations play a substantial role in the global dynamics of the RFP and much work has been carried out previously to characterize magnetic tearing mode behavior in the RFP. 5,[27][28][29][30][31][32][33] Direct measurements of the tearing mode spectrum in the core of MST are not available for any quantity, including magnetic fields. Nevertheless, magnetic mode spectral mea- surements are routinely made at the plasma wall by arrays of magnetic coils.…”

Section: B Extracting Tearing Mode Flowsmentioning

confidence: 99%

Local measurements of tearing mode flows and the magnetohydrodynamic dynamo in the Madison Symmetric Torus reversed-field pinch

et al. 2010

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The first localized measurements of tearing mode flows in the core of a hot plasma are presented using nonperturbing measurements of the impurity ion flow. Emission from charge exchange recombination is collected by a novel high optical throughput duo spectrometer providing localized ͑Ϯ1 cm͒ measurements of C +6 impurity ion velocities resolved to Ͻ500 m / s with high bandwidth ͑100 kHz͒. Poloidal tearing mode flows in the Madison Symmetric Torus reversed-field pinch are observed to be localized to the mode resonant surface with a radial extent much broader than predicted by linear magnetohydrodynamic ͑MHD͒ theory but comparable to the magnetic island width. The relative poloidal flow amplitudes among the dominant core modes do not reflect the proportions of the magnetic amplitudes. The largest correlated flows are associated with modes having smaller magnetic amplitudes resonant near the midradius. The MHD dynamo due to these flows on the magnetic axis is measured to be adequate to balance the mean Ohm's law during reduced tearing activity and is significant but does not exclude other dynamo mechanisms from contributing during a surge in reconnection activity.

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“…29 The observations of discrete relaxation in the RFP plasmas showed that the relaxation may go on in an oscillatory manner. The loop voltage, reversal parameter, and electron current all have sawtooth character [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] during the relaxation. The loop voltage and fluctuation amplitudes peak at the sawtooth crash.…”

Section: Jϭ"؋bϭb ͑1͒mentioning

confidence: 99%

“…63. Since the MHD dynamo action was introduced into the RFP plasma, 55 the MHD dynamo theory has enjoyed considerable success in the physics of the laboratory plasma and is well supported by the experimental phenomenology [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] and the numerical simulations. 66 -77 It is of great importance to the physics of the RFP plasma that the MHD dynamo electric field and mean-field Ohm's law have been verified in the recent experiment.…”

Section: Jϭ"؋bϭb ͑1͒mentioning

confidence: 99%

“…30 The cycle goes on and forms the discrete relaxation process which is probably responsible for the ''discrete dynamo events'' observed in the experiments. 15,[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] Now we discuss the fluid velocity U. The kinetic energy is dissipated by the viscosity, especially, the turbulent viscosity.…”

Section: Sawtooth Relaxation In Rfp Plasmasmentioning

confidence: 99%

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Model for relaxation in reversed-field pinch plasmas

Wang

Qiu

1996

Physics of Plasmas

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In this article, a model for anomalous ion heating, a dynamo current-sustained edge toroidal field, and a sawtooth oscillation during the relaxation in the reversed-field pinch ͑RFP͒ plasma is presented. The dynamo ͑␣͒, the turbulent resistivity ͑␤͒ and viscosity ͑͒, dependent on the magnetohydrodynamics ͑MHD͒ fluctuations, are incorporated into the model. Turbulent viscous dissipation of the fluctuation energy is proposed as the mechanism of the anomalous ion heating. This is a straightforward corollary of the turbulent viscosity heating of ions in that the temperature of the heavier ions is higher than that of the lighter ions and that the ion temperature increases with the MHD fluctuation level. Correspondingly, the turbulent resistivity heats electrons anomalously. It is shown that the dynamo current, generated by the back-transfer of fluctuating magnetic field helicity to mean magnetic field, sustains the RFP magnetic configuration. In the edge the total current density is approximately equal to the dynamo current density, while at the core the dynamo current opposes the applied electric-field-driven current, flattening the current profile. Provided the ␣ dynamo has a periodic behavior in time, the physical quantities of the RFP plasma have a sawtooth time dependence. The local poloidal current density in the edge increases during the sawtooth crash and peaks at the end of the crash, as do the ion and electron temperatures. In contrast, the toroidal current density at the core decreases during the crash and arrives at its minimum at the end of the crash. Qualitatively, the conclusions drawn from the present model are in good agreement with many of the experimental results ͓Scime et al., Phys. Rev. Lett. 68, 2165 Ji et al., ibid. 73, 668 ͑1994͔͒ and the numerical simulations.

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Asymmetric magnetic flux generation, m=1 activity, and edge phenomena on a reversed-field pinch

Cited by 49 publications

References 24 publications

Simulation Study of Self-Organization and Self-Relaxation Processes in Plasma

Simulation Study of Self-Organization and Self-Relaxation Processes in Plasma

Local measurements of tearing mode flows and the magnetohydrodynamic dynamo in the Madison Symmetric Torus reversed-field pinch

Model for relaxation in reversed-field pinch plasmas

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