A Current-Mode Triple Langmuir Probe methodology for the investigation of unsteady, small

Summary form only given. The applicable range of a Current-Mode Triple Langmuir Probe (CM-TLP) has been extended towards transient, sub- centimeter scale plasmas, requiring augmentations to existing theory of operation as well as bias circuit design optimization. These improvements are validated through the CM-TLP characterization of a small-scale plasma jet produced by a Micro Liquid-fed Pulsed Plasma Thruster prototype developed and MEMS fabricated at the Johns Hopkins University Applied Physics Laboratory. The CM-TLP theory of operation for the thin-sheath and the transitional regimes is expanded to include the Orbital Motion Limited regime applicable to low density plasmas. An optimized CM-TLP bias circuit employing operational amplifiers in both a differential amplifier configuration as well as a voltage follower configuration has been developed to adequately amplify current signals in instances where traditional current measuring techniques are no longer valid. This research also encompasses novel sub-microampere signal amplification in the presence of substantial common-mode noise as well as several a priori electromagnetic interference elimination and filtering techniques. The CM-TLP wires were designed with a radius of 37.5 Icircfrac14m and length of 5 mm. Measurements were taken at 2.0 cm, 6.0 cm and 10.0 cm locations from the exit of the plasma source using a linear translation stage. Results indicate a peak electron temperature of 13.59 eV at 2.0 cm from the exit. Electron number density for the 2.0 cm case is relatively volatile, with an observed peak of 3.18xl018 m"3 occurring at 0.3 ms after discharge initiation. Characterization of the plasma has confirmed the reliability and accuracy of time- resolved measurements via a CM-TLP methodology as extended to small-scale, relatively high-density plasmas.