Measurement of the thrust generated by a hollow cathode with noble gases

Abstract

Hollow cathodes (HCs) have been used for decades in various electric propulsion applications.  In spite of this, understanding and modelling of the HC discharge physical mechanisms is still far from satisfactory.  Further investigations are therefore necessary.  In particular, the thrust generated by a HC has actually been measured only in one instance, with a device quite different from the one investigated in this thesis.  A thrust measurement system has therefore been developed, in order to evaluate for what discharge conditions the highest values of specific impulse and in general the best performance are attained.  The system consists of a Cantilever beam Target (CBT) and of a Laser Optical Level (LOL).  Extensive thrust measurements with several noble gases as propellants are presented and discussed.  They show that several mN of thrust can be produced, at values of specific impulse exceeding, in some cases, 500s.  Such values confirm that the device is not just heating the gas, like a resistojet, but is operating in a fashion more similar to that of an arcjet, with the heavy particle average temperature sensibly higher than the wall value.  These encouraging results were obtained just by varying the discharge parameters, with very little attempt at optimising the electrode configuration. The use of different electrode configurations, like for instance and enclosed keeper, and the investigation of other propellants, could lead to the development of a viable HC microthruster, competitive with already existing devices.

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