An electron cyclotron resonance plasma source is built by arranging SmCo magnets to form a multicusp magnetic field with axial magnetic plugging. The source is tested in H2, N2, and Ar by the microwave of 2.45 GHz in the range from 10−2to 10−3Pa. The discharge sustaining power is measured as a function of pressure. The plasma density, the average electron energy, and the electron energy distribution are measured by using a Langmuir probe. Plasma is obtained at pressures as low as 10−3Pa in Ar. The average electron energy and the ion density increase with the feed microwave power. The electron energy distribution shows depletion at the low‐energy part. Ion spectra obtained in Ar show a multicharged state up to Ar8+. ©1994 American Institute of Physics.