Comparison of resonant magnetic perturbation induced particle transport changes in H-mode (DIII-D) and L-mode (MAST)

Comparison of resonant magnetic perturbation induced particle transport changes in H-mode (DIII-D) and L-mode (MAST)

Comparison of resonant magnetic perturbation induced particle transport changes in H-mode (DIII-D) and L-mode (MAST) 150 150 Mathew

Comparison of resonant magnetic perturbation induced particle transport changes in H-mode (DIII-D) and L-mode (MAST)

Recent experiments show the impact of Resonant Magnetic Perturbations on the density [O Schmitz et al Plasma Phys. Control. Fusion 50 124029 (2008); T E Evans et al Nucl. Fusion 48 024002 (2008); A Kirk et al Nucl. Fusion 50 024002 (2008); Y Liang et al Phys. Rev. Lett. 98 265004 (2007)], leading to a so-called density pump-out. Previous comparisons between DIII-D and TEXTOR have focussed on the similarities of the deformation of the separatrix and the creation of striations at the intersection of the main chamber wall [O Schmitz et al Plasma Phys. Control Fusion 50 124029 (2008); O Schmitz et al Phys. Rev. Lett. 103 165005 (2009)]. In this paper, we compare the difference in magnitude of the experimentally observed density pump-out in L-mode with H-mode in two diverted tokamaks: MAST and DIII-D. In order to address the differences in magnetic field from the coils, plasma shape and q 95 between the two devices, we compute a weighted magnetic diffusion coefficient with a vacuum field line tracing code. This allows us to compare the changes in density pump-out with the weighted magnetic diffusion coefficient, using a simple particle diusion model. We find that the density pump-out is vastly different in the two devices, suggesting different particle transport mechanisms. Since one main difference in transport characterics between L- and H-mode is turbulence, we compare turbulent particle characteristics. We find that in L-mode (MAST) the fluctuations and E x B shear increase at the plasma edge, whereas in H-mode (DIII-D) the fluctuations decrease at the plasma edge. Deeper inside the core, the E x B shear remains similar in L-mode (MAST), whereas a large decrease that quickly saturates with RMP strength is observed in H-mode (DIII-D). These results suggest that the RMP induced particle transport at the plasma edge in L-mode (MAST) is the result from increases in turbulent particle transport, whereas the results in H-mode (DIII-D) suggest a decrease in turbulent particle transport.

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01/01/2011