Patent ID: 7696758

Claim:
A plasma diagnostic apparatus including a probe unit inserted into a plasma or disposed at a boundary of a plasma, the apparatus comprising: a signal supplying unit having a signal supplying source; a current detecting/voltage converting unit for applying a periodic voltage signal applied from the signal supplying unit to the probe unit, detecting the magnitude of the current flowing through the probe unit, and converting the detected current into a voltage; and a by-frequency measurement unit for receiving the voltage output from the current detecting/voltage converting unit as an input and computing the magnitude of individual frequency components of the current flowing through the probe unit; wherein an ion density (ni) of the plasma is computed from the computed individual frequency components of the current by following Equation: n i = 2 ⁢ i k , w ⁢ I 0 ⁡ ( V sh T e ) 0.61 ⁢ eu B ⁢ AI k ⁡ ( V sh T e ) where Te is an electron temperature, Vsh is the magnitude of the sheath voltage between a probe unit and a plasma, A is a probe area, and ikw is a magnitude of kth harmonic frequency of the current flowing through a probe unit.