Experiments have shown that especially the radial magnetic field component plays a crucial role in the production of highly charged ions with Electron Cyclotron Resonance Ion Sources(ECRIS).However,in several room temperature operating ECRISs the radial magnetic field strength is below the optimum value,mainly due to the limits in permanent magnet technology.Remarkable radial magnetic field improvement can be reached with a relatively simple and cost-effective idea called Modified MultiPole Structure (MMPS).The MMPS differs strongly from the former structures because here the magnetic field is increased only locally without affecting the plasma size.The idea was studied experimentally with a new MMPS plasma chamber prototype.which was designed and constructed for the JYFL 6.4GHz ECRIS.The new chamber is versatile and made it possible to perform several new types of measurements.These showed that the MMPS is especially applicable to increase very high charge-state ion production.Typically the ion current increases more than a factor of 2 in the case of highly charged ions such as Ar16+.