Plasma parameter measurement by the impedance of a coil inductively coupled with a plasma

We have developed a method to measure plasma parameters in a discharge by a nalyzing the impedance of a search coil wound around a discharge tube. This technique is based on the diamagnetic characteristic of the plasma. When a high-frequency current passes through the search coil, a diamagnetic curre nt is induced inside the plasma, and the energy to the search coil is dissi pated by Joule loss due to the resistivity of the plasma. As a result, the impedance of the search coil varies depending on plasma properties. The rel ationship among plasma parameters, magnetic field and impedance of the sear ch coil is derived from Maxwell's equations and generalized Ohm's law. Thus , plasma parameters can be determined from the variation of the impedance. The present diagnostic method was applied to measure electron density and e lectron temperature in a mercury-argon plasma at a pressure of 2.5 Torr.