Self-calibrated measurement of ion flow using a fine multihole directional langmuir probe

A fine multihole directional Langmuir probe (FM-DLP) has been developed to measure ion Mach number and tested in an electron cyclotron resonance (ECR) plasma. It is found that the FM-DLP can measure the ion Mach number with the same method used for a conventional directional Langmuir probe (DLP). Moreover, the sensitivity of the FM-DLP is almost twice as high as that of the conventional DLP by changing the aspect ratio of the hole that collects ion saturation current. It is also found that the electron saturation current of the FM-DLP is markedly reduced to the level of ion saturation current; thus, the current-voltage characteristics of the FM-DLP become similar to those of an emissive probe, which suggests the emissive-probe-like function of the FM-DLP. We have demonstrated that the FM-DLP can measure the plasma potential, which enables us to determine the calibration factor without other diagnostic tools. Therefore, it is concluded that the FM-DLP has a self-calibration capability for ion flow measurement. © 2010 The Japan Society of Applied Physics.