In the RFP edge, measured transport and flows are strongly influenced by magnetic islands [1]. In fact, these islands determine a differential radialdiffusion of electrons and ions which, interacting with the wall, give rise to a characteristic edge ambipolar potential. A natural analogue of this phenomenology are the resonant magnetic perturbations (RMPs), applied in tokamaks to reduce ELM's. They impose a characteristic modulation to the edge electron density and temperature fields, in close correlation with the local magnetic vacuum topology [2]. Measurements of plasma potential inside an m/n=4/1 island in the edge of the TEXTOR Tokamak suggest the island is a particle pumping out region enhancing the transport. In order to understand if a unified picture of the particle transport is possible and there are any similarities in the phenomena observed in tokamak devices with RMP (such as the particle pumpout) and in RFP (such as convective cells in the edge), test particle transport simulations similar to replicate the study performed for RFX-mod have been done on TEXTOR with the guiding-center code ORBIT [3]. This versatile numerical tool allows to obtain plots of the parallel connection length of thermal electrons to the wall as L ? (r,?) ? v th ? trav(? travbeing the electron travel time between the initialand final positions and v th the thermal velocity), to be compared to the connection lengthsof RMPs [4]. Besides this, ORBIT calculates density distributions of test ions or electrons in the (r,?) plane, whose differences, especially around the X-points of islands, allow for an initial estimate of the radial electric field E r . Finally, a map of the simulated ambipolar field can be compared with m/n=4/1 island plasma potential measurements. References [1] N.Vianello, in Proc. 24th IAEA Fusion Energy Conference (2012), paper EX/P8-02 [2] O. Schmitz, Nucl.Fusion 52 054001 (2012) [3] White R.B. and Chance M.S. Phys. Fluids 27 2455-2467 (1984) [4] G. Spizzo, et al., Nuclear Fusion 52 054015 (2012)
Edge islands transport in tokamaks and RFPs
M Agostini;M E Puiatti;P Scarin;G Spizzo;N Vianello;
2013
Abstract
In the RFP edge, measured transport and flows are strongly influenced by magnetic islands [1]. In fact, these islands determine a differential radialdiffusion of electrons and ions which, interacting with the wall, give rise to a characteristic edge ambipolar potential. A natural analogue of this phenomenology are the resonant magnetic perturbations (RMPs), applied in tokamaks to reduce ELM's. They impose a characteristic modulation to the edge electron density and temperature fields, in close correlation with the local magnetic vacuum topology [2]. Measurements of plasma potential inside an m/n=4/1 island in the edge of the TEXTOR Tokamak suggest the island is a particle pumping out region enhancing the transport. In order to understand if a unified picture of the particle transport is possible and there are any similarities in the phenomena observed in tokamak devices with RMP (such as the particle pumpout) and in RFP (such as convective cells in the edge), test particle transport simulations similar to replicate the study performed for RFX-mod have been done on TEXTOR with the guiding-center code ORBIT [3]. This versatile numerical tool allows to obtain plots of the parallel connection length of thermal electrons to the wall as L ? (r,?) ? v th ? trav(? travbeing the electron travel time between the initialand final positions and v th the thermal velocity), to be compared to the connection lengthsof RMPs [4]. Besides this, ORBIT calculates density distributions of test ions or electrons in the (r,?) plane, whose differences, especially around the X-points of islands, allow for an initial estimate of the radial electric field E r . Finally, a map of the simulated ambipolar field can be compared with m/n=4/1 island plasma potential measurements. References [1] N.Vianello, in Proc. 24th IAEA Fusion Energy Conference (2012), paper EX/P8-02 [2] O. Schmitz, Nucl.Fusion 52 054001 (2012) [3] White R.B. and Chance M.S. Phys. Fluids 27 2455-2467 (1984) [4] G. Spizzo, et al., Nuclear Fusion 52 054015 (2012)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
