Diagnostic studies of a low-pressure inductively coupled plasma in argon using a double Langmuir probe

The electron temperature and electron number density of a laboratory-built low-pressure inductively coupled plasma (LP-ICP) were measured using a double Langmuir probe. The probe was composed of two 0.5 mm diameter tungsten wires and a magnesia sleeve shielding the wires that could be linearly moved in the central channel of the plasma by a vacuum linear-motion feedthrough. The role of parameters was studied at a height of 25 mm above the load coil, which yielded an electron temperature of 3-6 eV and an electron number density of 2.5-5 x 10(13) cm(-3). Less dependence on operating factors was noticed at higher observation heights, and when water loaded on the low-pressure plasma was increased, the electron temperature and electron number density were reduced, unlike with an atmospheric ICP.