In magnetically confined experiments the presence of rational surfaces modifies the magnetic configuration with one or more islands embedded in the main plasma. The islands strongly influence particle and heat fluxes, hence their role must be included in the study of the transport properties. For this reason a new approach in modelling transport in presence of islands is presented: this method, dubbed Multiple Domains Scheme (MDS), with some simplifying assumptions, is directly applicable to 1.5D transport codes. In MDS three regions (core, island and outer part) are identified inside the plasma, all interfaced by the separatrix that acts as common boundary through which thermal and particle fluxes can be exchanged. In each domain a monotonic radial coordinate can be chosen and the metric elements can be computed accordingly. The MDS has been implemented in a new numerical tool, called Multiple Axis Solver (MAxS) [1]. To build a straight-field-line coordinate system and to compute the metric elements needed by MAxS, a new method that starts from discretized (Poincaré) magnetic field maps has been also developed [2]. Thanks to its flexibility, MAxS can be exploited to study transport in various plasma configurations: its application to LHD, a heliotron device, and to RFX-mod, a Reversed Field Pinch machine, is here presented. In LHD, a large m/n=1/1 magnetic island can be induced in the edge region by means of external coils. In stationary condition, the island alters the kinetic quantities appearing, for example, as a flat region in the electron temperature profile. To properly test the cross-field diffusivity in background plasma and inside of the island region, perturbative methods, such as heating modulation or pellet injection, are preferable. In previous works [1,3] a clear reduction of the transport in the island region has been found. Those studies have been performed, for simplicity, starting with a magnetic field given by the vacuum component. Now, the comparison of the transport properties of plasma with islands in LHD using the vacuum field and the more realistic finite beta configuration will be presented.
Study of transport modulation by magnetic islands in different magnetic configurations
Predebon I;Spagnolo S;
2018
Abstract
In magnetically confined experiments the presence of rational surfaces modifies the magnetic configuration with one or more islands embedded in the main plasma. The islands strongly influence particle and heat fluxes, hence their role must be included in the study of the transport properties. For this reason a new approach in modelling transport in presence of islands is presented: this method, dubbed Multiple Domains Scheme (MDS), with some simplifying assumptions, is directly applicable to 1.5D transport codes. In MDS three regions (core, island and outer part) are identified inside the plasma, all interfaced by the separatrix that acts as common boundary through which thermal and particle fluxes can be exchanged. In each domain a monotonic radial coordinate can be chosen and the metric elements can be computed accordingly. The MDS has been implemented in a new numerical tool, called Multiple Axis Solver (MAxS) [1]. To build a straight-field-line coordinate system and to compute the metric elements needed by MAxS, a new method that starts from discretized (Poincaré) magnetic field maps has been also developed [2]. Thanks to its flexibility, MAxS can be exploited to study transport in various plasma configurations: its application to LHD, a heliotron device, and to RFX-mod, a Reversed Field Pinch machine, is here presented. In LHD, a large m/n=1/1 magnetic island can be induced in the edge region by means of external coils. In stationary condition, the island alters the kinetic quantities appearing, for example, as a flat region in the electron temperature profile. To properly test the cross-field diffusivity in background plasma and inside of the island region, perturbative methods, such as heating modulation or pellet injection, are preferable. In previous works [1,3] a clear reduction of the transport in the island region has been found. Those studies have been performed, for simplicity, starting with a magnetic field given by the vacuum component. Now, the comparison of the transport properties of plasma with islands in LHD using the vacuum field and the more realistic finite beta configuration will be presented.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
