In previous tests on FEEP thrusters, the traditional propellant feeding system, based on the storage of pure cæsium, showed some drawbacks. The seals in the propellant tank had to be extremely tight for two reasons; firstly, and most importantly, cæsium is highly reactive with water vapour. Secondly, cæsium has strong wetting properties and this can often lead to leakage. It was proposed to try overcome these problems by storing the propellant as a chromate compound, Cs2CrO4, that is inert to water vapour. In this way, cæsium is safely contained prior to use, and is released upon thermal decomposition. The experiments here reported were aimed at testing this feeding system, consisting of a heating unit and a cartridge loaded with the Cs2CrO4 powder, when connected to a 3 cm FEEP emitter. The cæsium was to exit the cartridge via a capillary tube and drip into a funnel which then led to the emitter. Ion emission was tried in continuous and pulsed modes, and the pulse characteristics showed excellent reproducibility. Different failure modes of the feeding system were identified, including cæsium vapour losses from the capillary and evaporation from the funnel, both causing cæsium deposition on the experimental equipment. Ion beam scanning was performed using electrostatic probes, showing, in several cases, uneven emitter slit wetting, probably due to the content in impurities in the Cs2CrO4 powder.

Experimental Behavior of FEEP Emitters Fed by a Caesium Chromate Tank

MARCUCCIO, SALVO;ANDRENUCCI, MARIANO
1994-01-01

Abstract

In previous tests on FEEP thrusters, the traditional propellant feeding system, based on the storage of pure cæsium, showed some drawbacks. The seals in the propellant tank had to be extremely tight for two reasons; firstly, and most importantly, cæsium is highly reactive with water vapour. Secondly, cæsium has strong wetting properties and this can often lead to leakage. It was proposed to try overcome these problems by storing the propellant as a chromate compound, Cs2CrO4, that is inert to water vapour. In this way, cæsium is safely contained prior to use, and is released upon thermal decomposition. The experiments here reported were aimed at testing this feeding system, consisting of a heating unit and a cartridge loaded with the Cs2CrO4 powder, when connected to a 3 cm FEEP emitter. The cæsium was to exit the cartridge via a capillary tube and drip into a funnel which then led to the emitter. Ion emission was tried in continuous and pulsed modes, and the pulse characteristics showed excellent reproducibility. Different failure modes of the feeding system were identified, including cæsium vapour losses from the capillary and evaporation from the funnel, both causing cæsium deposition on the experimental equipment. Ion beam scanning was performed using electrostatic probes, showing, in several cases, uneven emitter slit wetting, probably due to the content in impurities in the Cs2CrO4 powder.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/25199
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