Angular resolved energy and particle flux measurements in a magnetized plasma

A flat probe allowing simultaneous energy flux and current density measurements as functions of an applied voltage was rotated in a homogeneous plasma. The probe dimensions (a) were larger or comparable to the ion gyro radius (r(i)). Current density (j(i)), floating potential (U-f), energy flux density (q), ion energy reflection coefficient RE and the sheath energy transmission coefficient gamma were determined as functions of the angle a between the probe surface normal and the magnetic field. For normal incidence conditions (alpha = 0) all measured quantities do agree well with the theoretical predictions. With \alpha\ approaching 90degrees, finite gyro-radii effects of the ions become important. To lowest order the angular variations can be understood by assuming Gamma(e,i) proportional to cos alpha + 2r(e,i)/a for the ion particle flux density. Most remarkably, a pronounced reduction of the floating potential and the ion impact energy was found experimentally at shallow angles. In contrast, relatively small angular dependencies were found for gamma and RE. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.