Macroscopic behavior and discrete dynamo in high-Θ reversed-field pinch discharges

Arimoto, Hideki; Nakamura, Akira; Sato, Koichi; Nagata, Akiyoshi; Ando, T.; Kubota, S.; Masamune, S.; Nagatsu, Masaaki; Tsukishima, Takashige

doi:10.1063/1.860820

Cited by 7 publications

(5 citation statements)

References 13 publications

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“…On the other hand, Eqs. ͑61͒-͑66͒, in which ␣, ␤, and practically decay away in relaxation time scale length and finally are almost equal to zero in the Taylor state, are only phenomenological and qualitatively coincident with the experimental phenomenologies [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] and the numerical simulations. 66 -76 Thus the quantitative results are desirable, but it is outside the scope of this article.…”

Section: Discussionsupporting

confidence: 67%

“…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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Section: Discussionsupporting

confidence: 67%

Section: Jϭ"؋bϭb ͑1͒mentioning

confidence: 99%

Section: Jϭ"؋bϭb ͑1͒mentioning

confidence: 99%

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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“…The amplitude of m = 0 modes is quite large (larger than the m = 1 modes in some cases). This relaxation is called the 'discrete dynamo event' [22,23]. After this event, the m = 1 mode starts to rotate again as before and the localized m = 0 mode slowly decays within 0.5-2 ms.…”

Section: Mechanism Of Self-organizationmentioning

confidence: 99%

Self-organization and its effect on confinement in a reversed field pinch plasma

Hirano¹,

Yagi²,

Maejima³

et al. 1997

Plasma Phys. Control. Fusion

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Results of self-organization of the magnetic field and associating plasma loss are reviewed in the reversed field pinch (RFP) experiments on TPE machines. It is shown that the RFP plasma has a strong tendency to relax to a certain magnetic configuration similar to the energy minimum state predicted by Taylor. Thus the RFP configuration is self-organized and self-sustained with appropriate control of experimental conditions. Interestingly, however, it is observed in some cases that the relaxation can take place without the conservation of total magnetic helicity.The mechanisms of the self-organization and associated loss are discussed in some detail. In the low pinch parameter region (<1.6), the self-organization is continuous and the main loss mechanism seems to be the electron motion along the stochastic magnetic field line caused by the overlapping of multiple modes of the magnetic fluctuations being excited simultaneously. In the high pinch parameter region, self-organization is characterized by the pulse-like relaxation (intermittent in many cases), which seems to destroy the magnetic surface in a certain position of the torus and causes rapid loss of plasma energy. Attempts to improve RFP confinement by controlling the relaxation are described. One example is the improved high-theta mode in TPE-1RM20 and another is the pulsed poloidal current drive in MST.

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