Methods of operating an electromagnet of an ion source for generating an ion beam with a controllable ion current density distribution. The methods may include generating plasma in a discharge space of the ion source, generating and shaping a magnetic field in the discharge space by applying a current to an electromagnet that is effective to define a plasma density distribution, extracting an ion beam from the plasma, measuring a distribution profile for the ion beam density, and comparing the actual distribution profile with a desired distribution profile for the ion beam density. Based upon the comparison, the current applied to the electromagnet may be adjusted either manually or automatically to modify the magnetic field in the discharge space and, thereby, alter the plasma density distribution.