Measurements of ion temperature by Langmuir probes in a non-magnetized plasma

The ion temperature is measured by using a combination of a very fine cylindrical probe and a large spherical probe in a non-magnetized plasma. In the region where the cylindrical probe radius is much smaller than the Debye radius, the ion saturation current collected by the probe is proportional to the product of the plasma density and the square root of the ratio of the electron to the ion temperatures. The spherical probe is used for the measurement of the plasma density. A sufficient agreement of the ion temperature measured by the present method with that by an electrostatic energy analyzer is obtained with the uncertainty of 35%. (auth.)