Instantaneous Direct-Display System of Plasma Parameters by Means of Triple Probe

A new electrostatic probe method utilizing the triple probe is proposed in which no voltage or frequency sweep (or switching) is required. This feature enables us to determine the instantaneous values of the electron temperature (Te), as well as the electron density (ne), within a short time which is of the order of the intrinsic response time of the probe itself (⪝1μsec). Moreover, the system allows the direct display of the Te values as well as the semidirect display of the ne values on appropriate display units, thus permitting us to eliminate almost all procedures usually required for data processing. In view of the features mentioned, this system may be a useful diagnostic tool not only for stationary plasmas but also for rapidly varying time-dependent plasmas of various types. This paper presents theoretical considerations for the instantaneous direct-display system using a symmetrical triple probe. Discussions are also presented for the estimation of errors caused by the variation of ion saturation current, for the application to magnetoplasmas, and for the time and spatial resolutions. Experimental confirmation was made through the measurements of stationary magneto- as well as non-magnetoplasmas. As an example of the application to time-dependent plasmas, the electron temperature waves accompanied by the moving striations in hydrogen discharge were observed.