THE SPATIAL PROFILES OF CHARGED-PARTICLES IN A MULTIPOLAR MAGNETICALLY CONFINED AR-O-2 PLASMA

The spatial profiles of charged particles in multipolar magnetically c onfined Ar-O-2 plasmas produced by do discharges are investigated by v arying the total pressure from 2 to 10 mTorr, the discharge current fr om 10 to 90 mA and the oxygen content from 4 to 20%. The measured spat ial negative ion and electron density profiles, which are approximated as a parabolic distribution and a uniform one except in the vicinity of the chamber wall, respectively, allow us to divide the entire disch arge into three regions: (i) an electronegative region, (ii) an electr opositive region and (iii) the sheath. The ratio of the negative ion d ensity to the electron density measured at the centre increases with i ncreasing oxygen content and pressure, but decreases with increasing d ischarge current. Oxygen content- and discharge current-dependences of the electronegative region's length are similar to those of the ratio , although the length does not strongly depend on the pressure. A glob al model, in which the flux balance equations for charged particles an d a power balance equation for electrons are taken into account, to es timate plasma parameters such as the individual charged particle densi ty and electron temperature is proposed, and then compared with the ex perimental results.