Ciaccio, G. and Schmitz, O. and Spizzo, G. and Abdullaev, S. S. and Evans, T. E. and Frerichs, H. and White, R. B. (2015) Helical modulation of the electrostatic plasma potential due to edge magnetic islands induced by resonant magnetic perturbation fields at TEXTOR. Physics of Plasmas, 22 (10). ISSN 1089-7674
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Abstract
The electrostatic response of the edge plasma to a magnet ic island induced by resonant magnet ic perturbations to the plasma edge of the circular limiter tokamak TEXT OR is analyzed. Measurem ents of plasma potential are interprete d by simulations wit h the Hamilton ian guiding center code ORBIT. We find a strong correlation between the magnetic field topology and the poloidal modulation of the measured plasma potential. The ion and electron drifts yield a predominantly electron driven radial diffusion when approaching the island X-point while ion diffusivities are generally an order of magnitude smaller. This causes a strong radial electric field structure pointing outward from the island O-point. The good agreement found between measured and modeled plasma potential connected to the enhanced radial particle diffusivities supports that a magnetic island in the edge of a tokamak plasma can act as convective cell. We show in detail that the particular, non-ambipolar drifts of electrons and ions in a 3D magnetic topology account for these effects. An analytical model for the plasma potential is implemented in the code ORBIT, and analyses of ion and electron radial diffusion show that both ion- and electron-dominated transport regimes can exist, which are known as ion and electron root solutions in stellarators. This finding and comparison with reversed field pinch studies and stellarator literature suggest that the role of magnetic islands as convective cells and hence as major radial particle transport drivers could be a generic mechanism in 3D plasma boundary layers.
| Item Type: | Article |
|---|---|
| Subjects: | 500 Scienze naturali e Matematica > 500.2 Scienze fisiche 500 Scienze naturali e Matematica > 530 Fisica > 530.7 Strumentazione 500 Scienze naturali e Matematica > 530 Fisica > 530.8 Misure 500 Scienze naturali e Matematica > 530 Fisica > 533 Meccanica dei gas > 533.7 Teoria cinetica dei gas 500 Scienze naturali e Matematica > 530 Fisica > 538 Magnetismo > 538.6 Magnetoidrodinamica 500 Scienze naturali e Matematica > 530 Fisica > 539 Fisica moderna > 539.7 Fisica atomica e nucleare |
| Depositing User: | Dr Gianluca Spizzo |
| Date Deposited: | 21 Dec 2016 13:42 |
| Last Modified: | 21 Dec 2016 13:42 |
| URI: | http://eprints.bice.rm.cnr.it/id/eprint/15467 |
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