Publication

The search for chaotic edge localized modes in ASDEX Upgrade

2004
Journal Articles

Abstract

Time intervals between edge localized modes (ELMs) from the ASDEX Upgrade tokamak have been analysed to determine whether the ELM dynamics is chaotic (deterministic) or random (noise dominated). Two different methods have been used to detect unstable periodic orbits or unstable fixed points, which are indicators of chaos, in the ELM time series. It has been found that these time series generally are noise dominated, with the notable exception of five individual discharges in which traces of chaos have been detected.

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2004
Journal Articles

Abstract

Official source

Related concepts (28)

Edge-localized mode

An edge-localized mode (ELM) is a plasma instability occurring in the edge region of a tokamak plasma due to periodic relaxations of the edge transport barrier in high-confinement mode. Each ELM burst is associated with expulsion of particles and energy from the confined plasma into the scrape-off layer. This phenomenon was first observed in the ASDEX tokamak in 1981. Diamagnetic effects in the model equations expand the size of the parameter space in which solutions of repeated sawteeth can be recovered compared to a resistive MHD model.

Stable manifold

In mathematics, and in particular the study of dynamical systems, the idea of stable and unstable sets or stable and unstable manifolds give a formal mathematical definition to the general notions embodied in the idea of an attractor or repellor. In the case of hyperbolic dynamics, the corresponding notion is that of the hyperbolic set. The gravitational tidal forces acting on the rings of Saturn provide an easy-to-visualize physical example. The tidal forces flatten the ring into the equatorial plane, even as they stretch it out in the radial direction.

Chaos theory

Chaos theory is an interdisciplinary area of scientific study and branch of mathematics focused on underlying patterns and deterministic laws of dynamical systems that are highly sensitive to initial conditions, and were once thought to have completely random states of disorder and irregularities. Chaos theory states that within the apparent randomness of chaotic complex systems, there are underlying patterns, interconnection, constant feedback loops, repetition, self-similarity, fractals, and self-organization.

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The search for chaotic edge localized modes in ASDEX Upgrade

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