Design of a hollow cathode thruster: concepts, parameter study and initial test results

Two electric propulsion concepts have been developed at Technische Universität Dresden as spin-off devices of regular hollow cathodes and initial testing has been conducted. Both devices represent millinewton thrusters that take advantage of thermionic electron emission using the low work function materials C12A7, LaB6, and thoriated tungsten in different design configurations. The first concept represents an electrothermal thruster which generates thrust by expanding and accelerating a heated propellant in a nozzle. Initial thrust measurement tests were carried out which showed thrust levels well above cold gas thrust, but low thrust efficiencies. The influence of different geometric parameters on the discharge properties and the performance is investigated and presented. The second thruster concept is a novel electromagnetic device in which charge carriers in a plasma discharge are accelerated by an applied magnetic field that is orthogonally oriented to the discharge current. Initial tests with C12A7 were not successful, but the functionality of the concept was shown by thrust measurements using a thoriated tungsten wire as an electron emitter.

Моделирование плазмы короткодугового ксенонового разряда сверхвысокого давления

We have studied a high- (ultrahigh-) pressure short-arc discharge in xenon with thoriated tungsten cathodes. A system of equations formulated based on earlier experimental data indicating possible emission of cathode material (thorium) into the discharge gap has made it possible to determine the electric field strength, plasma temperature, and concentration of thorium atoms as well as thorium and xenon ions in the plasma. The problem has been solved for a model discharge between planar electrodes. The results indicate the key role of thorium atoms in the cathode region. Thorium atoms determine the ionization balance and other electrokinetic properties of plasma. Emission of thorium atoms reduces the plasma temperature at the cathode, which turns out to be noticeably lower than the plasma temperature near the anode; this is a new result that agrees with experimental data. Other electrokinetic characteristics of the plasma (in particular, charged particle concentration and electric field strength) are also in good agreement with the experiment.

Energy distribution of electrons under axial motion in a quadrupole Penning trap

We present results of the energy distribution function of trapped electrons through a measurement of their axial oscillation in a quadrupole Penning trap. Electrons emitted from a thoriated tungsten filament with a range of energies (3–5 eV) are trapped in a low magnetic field quadrupole Penning trap. Subsequent to storage the trapped electrons are detected through monitoring their axial oscillations by an electronic tank circuit that is weakly coupled to the trap, by resonant energy transfer to the electrons. The technique, developed using LabVIEW, enables a direct measurement of the energy distribution function of the electrons in the trap. We obtain a normal distribution of energy, with a maximum that coincides with the potential applied on the electron filament, indicating that the energy distribution of electrons in the trap reflects the energy distribution of the thermionically emitted electrons from the filament.