Open Access

Werner Ernst Schabert

• The H-mode is an improved confinement regime for tokamak reactors, in which the performance of individual devices improves typically by a factor of two or more. Fusion capabilities of future tokamaks can be greatly enhanced, if they can access this operational regime. However, the H-mode is often perturbed by an intermittent series of relaxation oscillations known as ELMs (edge-localized modes), which show bursts of MHD activity and a fast (0.1 ms) loss of particles and energy from the plasma. The analytical understanding of the H-mode and the ELMs can benefit from the fact that the dynamics of plasmas can in many cases be reduced to low-dimensional mathematical models. An important technique for obtaining details of the dynamics of the plasma from measured data is given by the method of delays, which creates a dynamical system that shows qualitatively the same behaviour as the investigated plasma. For the investigation of the plasma dynamics, data from COMPASS-D is used, whichThe H-mode is an improved confinement regime for tokamak reactors, in which the performance of individual devices improves typically by a factor of two or more. Fusion capabilities of future tokamaks can be greatly enhanced, if they can access this operational regime. However, the H-mode is often perturbed by an intermittent series of relaxation oscillations known as ELMs (edge-localized modes), which show bursts of MHD activity and a fast (0.1 ms) loss of particles and energy from the plasma. The analytical understanding of the H-mode and the ELMs can benefit from the fact that the dynamics of plasmas can in many cases be reduced to low-dimensional mathematical models. An important technique for obtaining details of the dynamics of the plasma from measured data is given by the method of delays, which creates a dynamical system that shows qualitatively the same behaviour as the investigated plasma. For the investigation of the plasma dynamics, data from COMPASS-D is used, which indicates the presence of several modes during the L-H transition and the H-mode. The analysis identifies a model due to Sugama and Horton as the most promising candidate among existing models to describe the L-H transition and the ELMs.…