Measurement of the plasma potential in a magnetron discharge and the prediction of the electron drift speeds

Summary form only given, as follows. Using an emissive probe the distribution of plasma potential Vp in the bulk plasma of a DC Magnetron discharge has been determined for a range of pressures (0.26, 0.53 and 0.78 Pa) and cathode voltages (between -236 and -338 V). The results reveal a large axial variation in the space potential in the confined plasma, with & DeltaV/sub p/ /spl sim/25 V over a distance of 5 cm, from plasma to target. By combining the derived electric field with the modelled magnetic field, the distribution of single particles drifts have been found, namely the, electron E/spl times/B, GradB and curvature drift speeds. The predicted E/spl times/B drift speeds (with values up to /spl sim/1.5/spl times/10/sup 5/ ms/sup -1/) are typically 2 to 3 times higher than the GradB and curvature drifts. The Hall current channel is a broad region extending from above the ´race-track´ down to a position close to the axis, 6 cm from the cathode. The calculated total Hall current is approximately 5 times the discharge current. Using a simple model of the discharge, in which a possible distribution of electron current throughout the plasma is considered, allows the determination of the ratio of the gyro-frequency to the collision frequency &omega/&nu locally in the bulk. Using this method, the maximum value of &omega/&nu is found to be /spl sim/25, which indicates that cross-field electron transport occurs more rapidly than from a classical prediction.