The efficiency of radio-frequency (RF) power absorption,RF magnetic field structure and plasma parameters were measured in cylindrical inductive RF plasma sources 20 cm in diameter and 22,32,53 cm in length with a low value external magnetic field.The experiments were carried out in argon at pressures of 13-140 mPa.The RF power supply changed from 200 W to 800 W.The spiral antenna was used for sustaining the discharge.It was shown that efficiency of RF power absorption depended nonlinearly on the external magnetic field values.At maximal values of the RF power absorption efficiency,the axial distributions of longitudinal Bz and azimuthal Bφ components of RF magnetic field manifested the formation of the partially standing wave with a half wavelength close to 8 cm.At the same conditions,the axial dependence of the radial RF magnetic field component Br differed drastically.It was concluded that the Bz and Bφ amplitudes were largely determined by the RF field of Trivelpiece-Gould wave,while Br amplitude represented the radial RF field of the helicon wave.