Nonlinear dynamics of kink-tearing modes and their interaction with the current profiles in a reversed-field pinch

Nordlund, P.; Mazur, S.

doi:10.1063/1.870873

Cited by 37 publications

(28 citation statements)

References 25 publications

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“…Transient states where the magnetic field fluctuations spatial spectrum is dominated by one individual (m = 1, n ∼ 2R/a) MHD mode, were first detected in all large RFP's [69][70][71][72][73][74], and found to last for several energy confinement times. Later on, the single helicity (SH) states found in MHD simulations [29], triggered the discovery in the data base of RFX of similar states lasting over the whole flat top at about 1 MA [76].…”

Section: Quasi Single Helicitymentioning

confidence: 97%

What is a Reversed Field Pinch?

Escande¹

2015

Rotation and Momentum Transport in Magnetized Plasmas

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Section: Quasi Single Helicitymentioning

confidence: 97%

What is a Reversed Field Pinch?

Escande¹

2015

Rotation and Momentum Transport in Magnetized Plasmas

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“…5 Experimental RFP plasmas in which the spectrum of mϭ1 modes condenses spontaneously to one dominant mode with a well defined toroidal number n have been observed in several devices. [6][7][8][9] In the RFX device these spectra have been observed to last for the entire discharge, and a helical coherent structure, hotter than the plasma nearby, is detected in the plasma core. 10 The ratio of the dominant to the other secondary modes is much smaller than for the theoretical SH state, hence these experimental spectra are referred to as quasi-single helicity ͑QSH͒.…”

mentioning

confidence: 99%

Quasi-single helicity spectra in the Madison Symmetric Torus

et al. 2002

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Evidence of a self-organized collapse towards a narrow spectrum of magnetic instabilities in the Madison Symmetric Torus [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] reversed field pinch device is presented. In this collapsed state, dubbed quasi-single helicity (QSH), the spectrum of magnetic modes condenses spontaneously to one dominant mode more completely than ever before observed. The amplitudes of all but the largest of the m=1 modes decrease in QSH states. New results about thermal features of QSH spectra and the identification of global control parameters for their onset are also discussed. (C) 2002 American Institute of Physics

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“…The QSH states have also been observed in other RFP experiments on several machines, such as RFX, 12 madison symmetric torus ͑MST͒, 13 EXTRAPT-II, 14 and TPE-RX. 15 The structure of plasma in the QSH state was measured on RFX in some detail, where the existence of a hot plasma core with a helical structure was clearly shown by soft-x-ray tomography measurement, which indicated the improvement of transport in the core region.…”

Section: Introductionmentioning

confidence: 69%

Quasi-single helicity state at shallow reversal in TPE-RX reversed-field pinch experiment

et al. 2005

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The operating conditions for obtaining a quasi-single helicity (QSH) state with a good reproducibility are found in a reversed-field pinch (RFP) experiment on the large RFP machine, TPE-RX [Y. Yagi et al., Fusion Eng. Des. 45, 421 (1999)]. In these conditions, the reversal of toroidal magnetic field (Bta) is maintained at a very shallow value (∼−0.2mT) after the setting up phase and the following fast current rising phase. After a certain period at this shallow reversal (∼15–25ms), the m∕n=1∕6 mode (m and n being the poloidal and toroidal Fourier mode numbers, respectively) rapidly grows and saturates before the termination of discharge. The growth of this mode dominates the other modes and the QSH state with m∕n=1∕6 is finally achieved. This QSH state can be sustained for a long period (up to ∼45ms) almost until the end of discharge by applying a delayed reversal of Bta with appropriate trigger timing and magnitude. The initial setup of the QSH states shows a reproducibility of almost 100%, but its sustainment for a long period shows a slightly reduced reproducibility (∼85%). The initial rapid growth of the single dominant mode is compared with the numerical results of linear stability and nonlinear three-dimensional (3D) calculations by assuming the experimental magnetic field profile estimated with a standard model. Linear calculations show that the m∕n=1∕6 mode has the maximum growth rate to the ideal magnetohydrodynamic instability and can explain the dominant growth of this mode. The 3D calculations also show a qualitative agreement with the experiment, where under some conditions the m∕n=1∕6 mode becomes dominant after an initial relaxation and continues to the end of the simulation. These results indicate that the present QSH state is the combined result of the linear growth and nonlinear saturation of a particular mode.

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Nonlinear dynamics of kink-tearing modes and their interaction with the current profiles in a reversed-field pinch

Cited by 37 publications

References 25 publications

What is a Reversed Field Pinch?

What is a Reversed Field Pinch?

Quasi-single helicity spectra in the Madison Symmetric Torus

Quasi-single helicity state at shallow reversal in TPE-RX reversed-field pinch experiment

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