An advanced configuration of minimum‐Bfield is designed for the electron cyclotron resonance (ECR) multicharged ion sources. The aim is to dramatically increase the efficiency of ion beam extraction by correcting the deformed magnetic flux tube containing hot plasma. The correction is performed by reversing the polarity of successive multipoles in the longitudinal direction. This method enables us to adopt the quadrupole that causes the greatest deformation. In addition, the most intense electron acceleration can be achieved with the quadrupole, since the radial field gradient is the largest of all multipoles.