Application of a quadruple probe technique to MPD thruster plume measurements

A new quadruple Langmuir probe diagnostic technique is applied to the plume of a pulsed magnetoplasmadynamic (MPD) thruster with argon propellant. The probe permits simultaneous measurement of electron temperature Te, density ne, and ion flow velocity u in the exhaust stream. For distances of 3-25 cm from the thruster face, Te is 8-1.5 eV, ne is 4.8-1.2 x 10 m~, and u is 0.7-1.8 x 10 m/s. The measurements suggest that the plume is well-collimated, and that the ion temperature is significantly higher than the electron temperature, consistent with an ion-conduction model of the thruster.