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Report No.

Extension of halo current model by introducing sheath constraints

Miyamoto, Seiji; Sugihara, Masayoshi*; Sugie, Tatsuo; Kusama, Yoshinori

Vertical displacement events (VDEs) and subsequent plasma major disruptions induce severe electromagnetic force on the vacuum vessel (VV) of the ITER machine. The force primarily dependent on the ratio of current quench time to the vessel resistive time constant, $$tau_mathrm{cq}/tau_mathrm{L/R}$$, and the vertical force on the VV increases with this ratio. In this presentation, the primary concern is the resistivity of halo, which determines $$tau_mathrm{cq}$$ and hence the maximum vertical force. The electrostatic sheath on the boundary between halo plasma and the wall is considered as a constraint on the halo current flowing into the wall. The sheath increases resistance of the halo path; the sheath adds the sheath resistance, and the limitation of halo current density restrains halo temperature and thereby conductivity from exceeding a certain value because the power input from joule heating is limited. These constraints were implemented in the disruption simulation model of DINA. A self-consistent simulation of ITER VDE scenario is presented, where halo resistance is determined based on the balance between joule heating and sheath transmission power.



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