The problem of calculating vertical electromagnetic force on the vacuum vessel of axisymmetric magnetic confinement fusion devices is reformulated to a linear response problem. It is theoretically shown that the treatment of currents in the vessel is reduced to a quantity calculated in the plasma region, the source term or input for vertical force. Vertical force emerges in response to the input, where the transfer function of the response originates in the electromagnetic shielding of the vessel. The model provides an analytical way of calculating vertical force. An example is given in application to a vertical displacement event in ITER. The derived analytical formula provides an approximate explanation of the current quench time dependence of the vertical force obtained using the DINA code.
Fast calculation of the tokamak vertical instability