The contour distributions of the trapping field for the X OY plane ((a), (b)), X OZ plane ((c), (d)), and Y OZ plane ((e), (f)) by analytical solutions ((a), (c), and (e)) and numerical solutions ((b), (d), and (f)). Here we use U = 10 kV and E_bias = −1.8 × 10⁶ V/m.