Hollow cathode life time modelling

Hollow Cathodes (HCs) are of primary importance in the field of electric space propulsion, being used as electron sources in ion and Hall-effect thrusters. Hence, their lifetime is a key factor in all these applications.<br/><br/>HCs have demonstrated the capability of providing up to 30,000 hours of operation, whereas no direct experimental data exist above this limit.<br/><br/>The importance of HC lifetime is a growing issue for deep space missions using<br/>propulsive systems based on ion or Hall-effect thrusters that may require longer<br/>lifetimes than those demonstrated up to now. To address these concerns about HCs and<br/>to prove the suitability of an ion thrusters based solar electric propulsion subsystem for<br/>future high-impulse missions (such as Bepi Colombo), a model able to predict the HC<br/>lifetime is needed.<br/><br/>The model that has been developed in this thesis consists of three parts: a barium oxide<br/>depletion model, a low work function surface coverage model and a plasma update<br/>procedure to calculate the effects that a change in the insert surface work function will<br/>produce on the cathode plasma.<br/><br/>The barium-oxide depletion model has been validated by comparing its results with<br/>experimental measurements performed at QinetiQ and NASA, showing a good<br/>quantitative agreement.<br/><br/>The low-work function surface coverage model is the first of its kind to include the<br/>effect of ion bombardment. The plasma update procedure, even if semi-empirical, is<br/>able to produce results that are in good agreement with the measurements.<br/><br/>Using these three models the lifetime of the NSTAR hollow cathode has been<br/>simulated, yielding predictions that are in good agreement with the theoretical<br/>expectations.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Coletti, Michele

Advisor dc:contributor.advisor

• Gabriel, Stephen