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- Chu, M.S., et al.
(författare)
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Physics of Plasmas Modeling of Feedback and Rotation Stabilization of the Resistive Wall Mode in Tokamaks
- 2004
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Ingår i: Physics of Plasmas. ; 11, s. 2497-
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Tidskriftsartikel (refereegranskat)abstract
- Steady-state operation of the advanced tokamak reactor relies on maintaining plasma stability with respect to the resistive wall mode ~RWM!. Active magnetic feedback and plasma rotation are the two methods proposed and demonstrated for this purpose. A comprehensive modeling effort including both magnetic feedback and plasma rotation is needed for understanding the physical mechanisms of the stabilization and to project to future devices. For plasma with low rotation, a complete solution for the feedback issue is obtained by assuming the plasma obeys ideal magnetohydrodynamics ~MHDs! and utilizing a normal mode approach ~NMA! @M. S. Chu et al., Nucl. Fusion 43, 441 ~2003!#. It is found that poloidal sensors are more effective than radial sensors and coils inside of the vacuum vessel more effective than outside. For plasmas with non-negligible rotation, a comprehensive linear nonideal MHD code, the MARS-F has been found to be suitable. MARS-F @Y. Q. Liu et al., Phys. Plasmas 7, 3681 ~2000!# has been benchmarked in the ideal MHD limit against the NMA. The effect of rotation stabilization of the plasma depends on the plasma dissipation model. Broad qualitative features of the experiment are reproduced. Rotation reduces the feedback gain required for RWM stabilization. Reduction is significant when rotation is near the critical rotation speed needed for stabilization. The International Thermonuclear Experimental Reactor ~ITER! @R. Aymar et al., Plasma Phys. Controlled Fusion 44, 519 ~2002!# ~scenario IV for advanced tokamak operation! may be feedback stabilized with babove the no wall limit and up to an increment of ;50% towards the ideal limit. Rotation further improves the stability.
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- Ericsson, David, 1979, et al.
(författare)
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A quasi-planar incident wave excitation for time-domain scattering analysis of periodic structures
- 2005
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present a quasi-planar incident wave excitation for time-domain scattering analysis of periodic structures. It uses a particular superposition of plane waves that yields an incident wave with the same periodicity as the periodic structure itself. The duration of the incident wave is controlled by means of its frequency spectrum or equivalently the angular spread in its constituting plane waves. Accuracy and convergence properties of the method are demonstrated by scattering computations for a planar dielectric half-space. Equipped with the proposed source a time-domain solver based on linear elements yields an error of roughly 1 percent for a resolution of 20 points per wavelength and second order convergence is achieved for smooth scatterers. Computations of the scattering characteristics for a sinusoidal surface and a random rough surface show similar performance.
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- Ericsson, David, 1979, et al.
(författare)
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Calculating the Scattering from Periodic Surfaces in Time Domain Using a FEM-FDTD Hybrid Code
- 2004
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Ingår i: EMB04, Computational Electromagnetics - Methods and Applications, Conference Proceedings. - 9163160765 ; , s. 74-79
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Konferensbidrag (refereegranskat)abstract
- In this paper, we apply a new method for calculating the scattering from periodic structures in time-domain. By carefully choosing the incident wave, simple periodic boundary conditions can be used to truncate the computational domain and there is no need to make a transformation of Maxwell's equations to deal with the time delay between the periodic boundaries for oblique incidence.
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