Reconstruction of the magnetic field configuration by use of novel MHD-EFIT model in TS-6 spherical tokamak merging experiment

We present procedures and results of the novel MHD-EFIT model to reconstruct the magnetic field configuration using the external magnetic probes and Rogowski coil data measured during the plasma formation and merging of TS-6 spherical tokamak.  In TS-6 merging experiments, it is possible to measure the magnetic field components directly right after plasma formation before plasma merging/ reconnection heating.

The current MHD-EFIT method utilizes the external plasma parameters to reconstruct the plasma shape and position at the end of merging process; however there is no information on magnetic field components during the merging process. The main goal of this work is to reconstruct the internal magnetic field values during the merging.

In order to reconstruct the internal magnetic field, a series of out of domain virtual zero size coils have been virtually installed to adjust the magnetic field to values measured at the external probes positions. To control the size of the plasma toroids, the total plasma current data obtained from the Rogowski coil are also used which leads to  4% absolute error between the numerical and experimental B_z at the mid-plane during the merging confirming the ability of MHD-EFIT to reconstruct the magnetic configuration during merging.