An Electrostatic Ion-guide and a High-resolution Thrust-stand for Characterization of Micro-propulsion Devices

Interest in microthrusters has grown significantly in the last two decades for possible applications in small satellites and deep space missions. This thesis is motivated by the need of experimental setup for characterization of microthrusters. In the first part of the thesis, a time-of-flight (ToF) mass spectrometer with an electrostatic ion-guide has been developed for characterization of electrospray microthrusters that can focus all mono-energetic emitted charges within about 23 degree emission half-angle on a small detector placed at a distance nearly 60 times larger than the diameter of the detector. This helps time-of-flight analysis from a large fraction of the emission in real time. Experiments performed with externally wetted tungsten emitters have shown up to 80% charge collection from a nearly 15 degree half-angle in positive and negative polarities of emission. From capillary emitters with about 40 degree emission half-angle, nearly up to 30% of the emission has been collected for ToF measurement. Despite accommodation of large beam spread and increase in flight time, flight time measurement has been possible quite accurately. In the second part of the thesis, a nano-Newton thrust stand has been developed that can measure thrust up to about 100 ÎŒN with a resolution of 10 nN from different types of microthrusters. The operating principle of the thrust stand is different from other nano-Newton thrust stands developed in the last few years and it works by measuring impingement force of the emitted particles on a suspended plate with a sensitive force sensor. The suspended plate possesses a natural frequency around 50 Hz, and, by a homodyne thrust measurement scheme, avoids coupling of facility vibrations with the measurement. The resolution is among the best reported so far from thrust stands that measure thrust directly on the thruster and the first of its type to demonstrate less than 3 ÎŒN resolution. The setup has been characterized with the help of a cold-gas ejecting capillary and an electrospray device. Experiments with cold-gas ejector have shown that thrusts can be resolved with 10 nN resolution and a minimum thrust of about 10 nN can be detected. Measurements up to 2-3 ÎŒN from the electrospray device has been demonstrated with the thrust stand and the results are within 50-150 nN from that obtained from indirect beam diagnostics.

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