Abstract
A new probe method is proposed. This method is based upon the idea that the end of a cylindrical probe affects the surface area of the sheath. The first stage of this method is to measure the sheath radius by using a variable-length structure. The procedure is to extrapolate the probe current to l=0 along the straight line of the plot of current vs. length of probe and to measure the slope of the straight line and thus to derive the radius of the sheath. Experimental results of ion sheath for Ar are fairly well consistent with the theoretical radius expected from simple theories, except for low plasma density. The discrepancy between the theory and the experiment is caused by the disturbance.
By taking into account a correction factors, namely, depletion in ion collection due to elastic scattering, plasma density can be exactly estimated by measuring the radius of ion sheath without having any know-ledge of the adequate space charge equation. Thus, the reliability of the probe method is increased.
