For a tokamak, the poloidal field control systems drive current in coils to provide the contributions to the total poloidal field. The current in each coil must be adjusted to achieve a large enough null field region and a proper loop voltage for the breakdown of the gas pre-fill and the initial ramp-up of the plasma current. Whether the vacuum field can be reconstructed precisely is very important to the optimizing of plasma breakdown. Two kinds of algorithms were investigated to calculate the vacuum field. The first algorithm, being a traditional algorithm used to calculate the vacuum field is based on Green’s function. The second algorithm, used to calculate the vacuum field is based on the Cauchy condition surface method, a method which was used to calculate the vacuum field at start-up for the first time. Comparing the calculation results of the algorithms for EAST, the results for flux and magnetic field agree well in the region that matter, which confirms the utility of the new method.
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