In astrophysical and laboratory plasmas chaotic quasi-periodical (CQP) phenomena are often observed. Very famous examples in astrophysics are the cycle of the sunspots, or the inversion of the earth magnetic field, likely linked to the dynamo processes in the sun and in the earth. In laboratory plasmas also CQP phenomena are frequent. Examples are the sawtooth activity observed in the core of the tokamak and of the Reverse Field Pinch (RFP), the edge localized modes (ELMs) activity detected at the edge of highly confined tokamak plasmas. In many cases a link between the magneto-hydro-dynamic stability, and the matter and energy transport in the system, can be hypothesized and at least qualitatively, inferred from the experimental measurements. In this paper a model that couple transport and stability is numerically solved for the RFP case in the attempt to interpret the experimental CQP oscillations of a dominant mode observed in the plasma core. The model is built taking into account some key experimental observations: (i) the antagonism between the dominant and the so called "secondary" modes; (ii) a threshold in the measured upper value of the dominant mode; (iii) the oscillations in phase with the dominant mode, of the electron temperature. Some critical points will be discussed in the paper, such as the large excursion in the transport coefficients needed to approximately fit the experiments, the role and nature of the nonlinear coupling between the dominant mode and the secondary modes.
Chaotic quasi periodical oscillations in Reversed Field Pinch plasmas
2015
Abstract
In astrophysical and laboratory plasmas chaotic quasi-periodical (CQP) phenomena are often observed. Very famous examples in astrophysics are the cycle of the sunspots, or the inversion of the earth magnetic field, likely linked to the dynamo processes in the sun and in the earth. In laboratory plasmas also CQP phenomena are frequent. Examples are the sawtooth activity observed in the core of the tokamak and of the Reverse Field Pinch (RFP), the edge localized modes (ELMs) activity detected at the edge of highly confined tokamak plasmas. In many cases a link between the magneto-hydro-dynamic stability, and the matter and energy transport in the system, can be hypothesized and at least qualitatively, inferred from the experimental measurements. In this paper a model that couple transport and stability is numerically solved for the RFP case in the attempt to interpret the experimental CQP oscillations of a dominant mode observed in the plasma core. The model is built taking into account some key experimental observations: (i) the antagonism between the dominant and the so called "secondary" modes; (ii) a threshold in the measured upper value of the dominant mode; (iii) the oscillations in phase with the dominant mode, of the electron temperature. Some critical points will be discussed in the paper, such as the large excursion in the transport coefficients needed to approximately fit the experiments, the role and nature of the nonlinear coupling between the dominant mode and the secondary modes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
