Presheaths in multi-dipole plasma

Summary form only given. Measurements of plasma presheath thickness as a function of pressure (0.5 to 2 mTorr) were made in a DC hot-filament produced multi-dipole plasma discharge. The presheath plasma potential near a negatively biased plate (D=10 cm) was mapped with an emissive probe. The inflection point method in the limit of zero emission was used. The probe measurement of the plasma potential were accurate to approximately 0.1 V. Measurements were made in plasmas based on nitrogen, argon and combinations of both gases. Experimental results were similar to those found in ECR magnetized plasmas. The presheaths were found to be regions of approximately constant electric field with characteristic lengths the order of the ion-neutral collision lengths. The results show contraction of the presheath as the pressure increased. Two competing processes affect the presheath. These are ionization and collisions with ionization becoming more important at lower pressures. Experimental results are compared to various presheath models.