A series of systematic tests have been carried out on the superconducting electron cyclotron resonance ion source SCECRIS at the Michigan State University National Superconducting Cyclotron Laboratory in order to better understand the role of different parameters which determine the performance of these sources. A relevant part of these tests has been focused on the role of magnetic field and microwave frequency, with the goal of demonstrating the capability of low frequency electron cyclotron resonance ion sources to produce high ion charge states, in spite of their relative low plasma density. This goal can be achieved using a very high magnetic confining field, according to the concept of a high B mode. A comparison of the source performance at 2.45 and 6.4 GHz for different levels of magnetic field is described in this article. ©1996 American Institute of Physics.