MEASUREMENT OF THE NEUTRAL PARTICLE DENSITY IN AN ELECTRON-CYCLOTRON-RESONANCE PLASMA BY RAYLEIGH-SCATTERING

The neutral atom density in an electron cyclotron resonance plasma has been directly measured for the first time using a combination of Rayleigh and Thomson scattering. The measurements were made in the source region of a 3 mTorr argon discharge, and indicated that the neutral atom density was at least 50% less than would be expected at a gas pressure of 3 mTorr. The decrease in the neutral atom density is attributed to the effect of ion-neutral charge exchange collisions in the plasma. The accuracy of the measurement was found to depend on the contribution of metastable atoms to the measured scattered signal.