Further investigations on low-density Hall accelerators

The Hall-Ion-Thrustor is well suited for the power range of 0.5 ... 10 kW. Interesting applications for this thrustor type are the use for a Van-Allen-probe and for orbit-to-orbit transfer. Based on theoretical considerations, the dependance of the thrustor efficiency on the magnetic field and on the length of the accelerator channel has been calculated. To reduce the anomalous electron back-flow, an external ion source should be used, which produces a homogenious ion beam. This can be obtained by an annular plasma source with a slit hollow cathode. Experiments have been carried out on two different accelerator types. HIT III has been operated with a power input of about 5 kW, a ratio of thurst to power of 25 mN/kW at a velocity of the argon plasma of 35 km/s. This means an electric efficiency of almost 50%. HIT IV has been operated with a power input up to 8 kW. At lower power levels the thrust to power ratio is about 30 ... 35 mN/kW at an exhaust velocity of some 25 ... 30 km/sec. (Author)