On the axisymmetric stability of tokamaks with ferromagnetic walls

On the axisymmetric stability of tokamaks with ferromagnetic walls

On the axisymmetric stability of tokamaks with ferromagnetic walls 150 150 amit lakhani
UKAEA-CCFE-PR(20)80

On the axisymmetric stability of tokamaks with ferromagnetic walls

Reduced activation ferritic steels are an attractive option for use in large structural components surrounding tokamak plasmas in future fusion power plants, but their ferromagnetic response to the confining magnetic fields must be properly understood. Simultaneously, the advantages of operating at high plasma elongation push tokamak designs toward scenarios which are more vulnerable to vertical displacement events. Passive conducting structures in present tokamaks slow these instabilities such that they may be feedback controlled, but the efficacy of this process is likely to be eroded by ferromagnetic effects. We approach two related analytical models – in cylindrical and spherical geometries – which qualitatively and quantitatively assess the impact of a ferritic steel wall on the vertical instability growth rate for a plasma of certain elongation. Distinct limits for magnetically thick and thin walls give key physical insight, but the dependence on magnetic permeability and wall geometry is in general quite complex. Equilibrium considerations, particularly with respect to radial force balance, are also encountered.

Collection:
Journals
Journal:
Physics of Plasmas
Publisher:
AIP (American Institute of Physics)
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