Publication Date:
2014-03-01
Description:
The traditional theory of the resistive wall modes (RWMs) in the toroidal fusion systems was developed assuming the magnetic permeability μ of the wall the same as the vacuum one μ 0 . Here, we analyze the dynamics of unstable RWMs at the presence of a ferromagnetic wall with μ ̂ ≡ μ / μ 0 ≤ 4 . This choice with μ ̂ = c o n s t corresponds to the saturated state of ferritic materials in a strong magnetic field, as it should be in a tokamak reactor. The study is based on the cylindrical dispersion relation valid for arbitrary s / d w , where s is the skin depth and d w is the wall thickness. This equation is solved numerically, and the solutions are compared with analytical asymptotes obtained for slow ( s ≫ d w ) and fast ( s ≪ d w ) RWMs. Within the model, only very slow RWMs are found insensitive to variations of μ ̂ , while slightly above the no-wall stability limit the growth rate of the modes increases with larger μ ̂ . It is shown that at s 〈 d w this increase is roughly given by a factor of μ ̂ compared to a similar case with μ ̂ = 1 . The dependence of the transition from slow to fast RWMs on μ ̂ is discussed, and the accuracy of the available analytical relations is evaluated.
Print ISSN:
1070-664X
Electronic ISSN:
1089-7674
Topics:
Physics