Locked modes in two reversed-field pinch devices of different size and shell system

Malmberg, Jenny-Ann; Brunsell, Per R.; Yagi, Y.; Koguchi, Haruhisa

doi:10.1063/1.1290281

Cited by 18 publications

(19 citation statements)

References 29 publications

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“…10 The modified theory for the RFP 9 was also applied to predict a mode amplitude threshold for locking in three RFP experiments. 9,[11][12][13] Consistency with the theory was found, in that mode amplitudes in locked plasmas were above the predicted threshold. Most recently, an estimate of the eddy-current torque was made to try to account for two cases of varying mode rotation behavior in a tokamak.…”

Section: Introductionsupporting

confidence: 66%

Observation of tearing mode deceleration and locking due to eddy currents induced in a conducting shell

et al. 2004

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Growth to large amplitude of a single core-resonant tearing mode in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch is accompanied by braking and eventual cessation of mode rotation. There is also a concurrent deceleration of bulk plasma rotation. The mode deceleration is shown to be well described by a time-dependent version of a magnetohydrodynamical model [R. Fitzpatrick et al., Phys. Plasmas 6, 3878 (1999)] in which a braking torque originates from eddy currents induced by the rotating mode in the conducting shell surrounding the plasma. According to the model, the electromagnetic braking torque is localized to the plasma in the immediate vicinity of the mode’s resonant surface, but viscosity transfers the torque to the rest of the plasma. Parametrizing the plasma viscous momentum diffusivity in terms of the global momentum confinement time, the model is used to predict both the momentum confinement time and the time evolution of the decelerating mode velocity. In both respects, the model is quite consistent with experimental data.

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Section: Introductionsupporting

confidence: 66%

Observation of tearing mode deceleration and locking due to eddy currents induced in a conducting shell

et al. 2004

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“…13 Moreover, the tearing modes generally lock in phase together, generating a toroidally localized strong magnetic perturbation, commonly called the "slinky" mode. 14,15 When the modes also lock to the wall, the slinky-wall interaction is increased, producing influx of wall impurities. 16,17 Instead, in the theoretically predicted single helicity ͑SH͒ regime, the dynamo is produced by the interaction of a single tearing mode with the velocity field produced by an electrostatic drift due to a small charge separation; 18 the SH plasma core is characterized by a magnetic island generated by the single mode and has no magnetic chaos.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch

et al. 2007

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In recent years, good progress toward a better understanding and control of the plasma performance in reversed-field pinch devices has been made. These improvements consist both of the discovery of spontaneous plasma regimes, termed the quasi single helicity ͑QSH͒ regime, in which part of the plasma core is no longer stochastic, and of the development of techniques for active control of plasma instabilities. In this paper, a systematic study of spontaneous QSH in the EXTRAP T2R device ͓P. R. Brunsell, H. Bergsaker, M. Cecconello et al., Plasma Phys. Control. Fusion 43, 1457 ͑2001͔͒ is presented. In this device, QSH states can occur spontaneously and it is associated with magnetic and thermal structures. A statistical analysis to determine the most favorable experimental conditions to have a transition to the QSH regime will be presented. The results described here are useful to understand the underlying properties of QSH regimes in view of future applications of the QSH active control in EXTRAP T2R; they are also important to have a comparison with the QSH studied in other devices.

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“…Many experimental observations [6][7][8][9][10][11][12][13][14][15] and theoretical studies [16][17][18] have been made regarding the mode-locking phenomenon. Many experimental observations [6][7][8][9][10][11][12][13][14][15] and theoretical studies [16][17][18] have been made regarding the mode-locking phenomenon.…”

Section: Introductionmentioning

confidence: 99%

“…Many experimental observations [6][7][8][9][10][11][12][13][14][15] and theoretical studies [16][17][18] have been made regarding the mode-locking phenomenon. A further investigation has been performed in the T2 device, 9,15 which is the former OHTE device. This localization of the mode amplitude causes an enhanced plasma wall interaction that could lead to engineering problems involving damage to the first wall and impurity influx.…”

Section: Introductionmentioning

confidence: 99%

Evolution process of the mode wall-locking and phase-locking in a reversed-field pinch plasma

Yagi¹,

Koguchi²,

Sakakita³

et al. 2001

Physics of Plasmas

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Wall-locking and phase-locking modes are studied in detail in a reversed-field pinch device, TPE-RX ͓Y. Yagi et al., Fusion Eng. Design 45, 409 ͑1999͔͒. These mode-locking phenomena arise from tearing instabilities. Wall locking means the stopping of mode rotations, and phase locking means the locking of the phases of multiple modes. Phase locking induces a toroidally localized enhanced magnetic amplitude. There are two types of mode-locking states in TPE-RX. One of them exhibits a clear phase-locked structure, while the other exhibits a weak toroidal localization. Both types show finite toroidal rotation during the current-rising phase of the discharge, and are eventually wall locked during the current flat-top phase. However, the rotation speeds are clearly different between the two types. Confinement properties are compared between the two types of mode-locking states. It is shown that the threshold for the mode amplitude necessary to wall lock the toroidal rotation, as well as the bifurcation of phase-locked structures, agrees with theoretical predictions ͓R. Fitzpatrick et al., Phys. Plasmas 6, 1168, 3878 ͑1999͔͒.

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Locked modes in two reversed-field pinch devices of different size and shell system

Cited by 18 publications

References 29 publications

Observation of tearing mode deceleration and locking due to eddy currents induced in a conducting shell

Observation of tearing mode deceleration and locking due to eddy currents induced in a conducting shell

Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch

Evolution process of the mode wall-locking and phase-locking in a reversed-field pinch plasma

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