Magnetic probe (B-dot) measurements in an inductively coupled plasma (ICP): techniques and results

Summary form only given. We will discuss B-dot (dB/dt) measurement techniques and how these measurements are used to determine the spatial distribution of the electric field (E) and the current density (J). In this part of the talk we will present the little discussed, yet extremely important details in probe measurements. Topics include: basic B-dot probe operation, an electrical circuit model of the probe, experimental system and probe considerations that maximize differential mode (actual) probe components and minimize common mode (extraneous) signals, calibration of the probe for determination of E and J, and the importance of a probe configuration and geometry which minimizes plasma current perturbation. In the second part of the talk we will present selected results of the axial spatial profiles of magnitude and phase of E(z) and J(z) determined in a cylindrical ICP with a planar coil. Families of curves, such as: variable power with constant frequency and gas pressure, and variable frequency with constant power and gas pressure, will be presented so that the general behavioral trends can be recognized. From the spatial distribution of E(z), the skin depth near the induction coil will be determined and compared with the skin depth calculated from the classical (local) theory. It will be shown that the measured values of skin depth are in fairly good agreements with the classical skin depths evaluated from Langmuir probe measurements.