One dimensional (1D) energy and particle di ffusion in a magnetized plasma rely on the presence of nested flux surfaces, which, fro m the geometrical point of view, provide a monotonic radial coordinate from the magnetic axis to the plasma edge. Resonant layers in the plasma may lead to the growth of magnetic islands, with the consequent breaking of the magnetic flux surfaces in that region of the plasma. This brings to multiple magnetic axes in the plasma domain, and to an intrinsically thre e dimensional (3D) nature of the transport problem. Since 1.5 transport codes need a monotonic radial coordinate, they cannot manage topologies with more than one ma gnetic axis; on the other side a proper fully 3D treatment of the problem is difficult and CPU-time demanding . In order to preserve a 1D geometrical description, a piecewise treatment where different radial coordi nates are defined in different domains around their own magnetic ax es has been developed [1]. In this contribution we present an altern ative method [2] based on the idea that the presence of magnetic islands does not impede making 1D transport calculations if the island region is excluded and then, eventually, treated separately. We present a simple way to modify the geometry (radial coordinate and relate d metric coefficients) in order to exclude the island region from the 'principal' plasma, wher e 1D transport is considered. The method would equally apply to a fully chaotic region, excluded from the conserved plasma. Comparison with the metrics obtained from Poincaré plots (in presence of magnetic islands) are shown, as well as applications to two types of plasma using the ASTRA transport shell [3] with appropriately modified metrics: Heliac (TJ-II, CIEMAT, Spain), and Heliotron (LHD, NIFS, Japan).
Radial transport studies in magnetized plasmas with islands
Predebon I;
2018
Abstract
One dimensional (1D) energy and particle di ffusion in a magnetized plasma rely on the presence of nested flux surfaces, which, fro m the geometrical point of view, provide a monotonic radial coordinate from the magnetic axis to the plasma edge. Resonant layers in the plasma may lead to the growth of magnetic islands, with the consequent breaking of the magnetic flux surfaces in that region of the plasma. This brings to multiple magnetic axes in the plasma domain, and to an intrinsically thre e dimensional (3D) nature of the transport problem. Since 1.5 transport codes need a monotonic radial coordinate, they cannot manage topologies with more than one ma gnetic axis; on the other side a proper fully 3D treatment of the problem is difficult and CPU-time demanding . In order to preserve a 1D geometrical description, a piecewise treatment where different radial coordi nates are defined in different domains around their own magnetic ax es has been developed [1]. In this contribution we present an altern ative method [2] based on the idea that the presence of magnetic islands does not impede making 1D transport calculations if the island region is excluded and then, eventually, treated separately. We present a simple way to modify the geometry (radial coordinate and relate d metric coefficients) in order to exclude the island region from the 'principal' plasma, wher e 1D transport is considered. The method would equally apply to a fully chaotic region, excluded from the conserved plasma. Comparison with the metrics obtained from Poincaré plots (in presence of magnetic islands) are shown, as well as applications to two types of plasma using the ASTRA transport shell [3] with appropriately modified metrics: Heliac (TJ-II, CIEMAT, Spain), and Heliotron (LHD, NIFS, Japan).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
