Quasi-single helicity state at shallow reversal in TPE-RX reversed-field pinch experiment
- Institute of Energy Technology, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba-shi, Ibaraki, 305-8568 (Japan)
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 (B{sub ta}) is maintained at a very shallow value ({approx}-0.2 mT) after the setting up phase and the following fast current rising phase. After a certain period at this shallow reversal ({approx}15-25 ms), 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 {approx}45 ms) almost until the end of discharge by applying a delayed reversal of B{sub ta} 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 ({approx}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.
- OSTI ID:
- 20782342
- Journal Information:
- Physics of Plasmas, Vol. 12, Issue 11; Other Information: DOI: 10.1063/1.2118728; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CHARGED-PARTICLE TRANSPORT
COMPUTERIZED SIMULATION
ELECTRIC CURRENTS
ELECTRIC DISCHARGES
HELICITY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
PLASMA
PLASMA INSTABILITY
PLASMA SIMULATION
RELAXATION
REVERSE-FIELD PINCH
STABILITY
THREE-DIMENSIONAL CALCULATIONS
TPE-RX DEVICE