A 3D electrostatic modeling of an inertial electrostatic confinement (IEC) fusion device been realized. Finite element method is considered in order to identify the potential and electrical fields inside the spherical device. Two different material types are examined for the holder part of the cathode by comparing the field results. Meanwhile, different structures of cathode spheres are investigated for the determination of minimal and maximal field values, thereby the effect of structures on the ion confinement process has been found. Parallel to our previous study, the porcelain holder presents better homogeneous field and at the center of the inner sphere. In addition, an increase of vertical rings on the inner grid affects the bottom corner of electrical potential, thereby ions are scattered to the entire region of the inner grid. There an optimal number of vertical rings should be considered for the inner grid so that one can achieve a better ion core at the middle of the grid for the confinement process.