A multipole magnetic field is applied in a multifilament plasma source. By changing the strength of the magnetic field, the instability of the discharge, the change of the density profile, and the increment of the ion density are investigated. It is shown that the stable plasma with a rather high density on the order of 1012cm−3and with a uniform density profile within ±5% over the 9‐cm diameter is obtained in the lower discharge current compared with the discharge without the magnetic field, and the total heater current of the filament can be reduced by about 10%. The ratio (0.93) of the discharge current to the heater current without a magnetic field is improved to 1.8 with the field.