Performance and Characterization of a Neutral Beam Propulsion Technology Demonstrator

A neutral beam propulsion technology demonstrator has been fabricated and tested. It uses gas diffusion neutralization to create a globally neutral plasma from an ion source. Thrust measurements for the neutral beam demonstrate that thrust at the very low 100 μN levels produced by this system can be measured during thermal drift of the variable amplitude hanging pendulum with extended range thrust stand. The beam energy, which exhibits good quantitative agreement with the thrust measurements, is measured as a function of neutralizer gas flow rate using a graphite calorimeter. A Faraday cup is used to measure the neutralization of the beam. These measurements generally exhibit quantitative agreement with predictive analytical and numerical models. Losses owing to the use of a grounded metal neutralizer are discussed, and it is quantitatively demonstrated through thrust, neutralization, and calorimetry measurements that the neutralizer is the source of the performance losses.