The dynamics of xenon atoms and ions expanding in the magnetic nozzle (MN) of a helicon plasma thruster is studied by means of near-infrared laser-induced fluorescence spectroscopy on resonant and metastable states. Fluorescence spectra are measured for several operating conditions inside and outside the thruster discharge chamber. In the near-field plume, the relatively intense magnetic field induces Zeeman effect on the probed optical transitions. Hence, modeling of the atomic lineshapes is addressed to accurately compute the Doppler shift and infer the velocity. The first direct measurements of the neutral flow in a MN reveal that atoms are accelerated to supersonic velocities behind the thruster exit. The ions acceleration region extends several centimeters downstream the exit plane. Larger axial ion speeds are attained when the thruster operates at lower mass flow rates and higher levels of input power.

Helicon plasma sources currently represent an active field of research in the domain of low-temperature plasmas due to several interesting characteristics for in-space propulsion applications. This work reports direct comparison of krypton and xenon plasma properties through spatially resolved measurements performed in the near-field plume of a sub-kilowatt-class 13.56 MHz helicon source. The set of developed and employed intrusive diagnostics is comprehensively described. The magnetic components of the plasma rf field are inferred using a 3D B-dot probe along the reactor axial direction with and without the externally applied DC magnetic field. Plasma floating potential fluctuations are measured using a capacitive probe to draw design requirements for a rf-compensated Langmuir probe. The latter is used to perform axial and radial measurements of plasma density, electron temperature, and plasma potential. A four-grids retarding potential analyzer is used to infer the ion kinetic energy downstream the source exit. The effect of magnetic field magnitude on ions and electrons properties is especially investigated.

Iodine is considered as a feasible alternative to xenon as a propellant for electric propulsion systems, thanks to its good propulsive performance, high availability, and high storage density. However, as iodine is stored in solid state at ambient temperature, current state-of-the-art propellant management systems are not suitable to be used with it. Moreover, due to its high reactivity, iodine imposes requirements on material-compatibility, hindering the use of mass flow measurement and control systems typically used with other propellants. The architecture of a controlled iodine feeding system for low power (200 W class) ion and Hall effect thrusters is presented and the resulting prototype is described. It consists of a sublimation assembly whose temperature is used to control the tank pressure, a normally-closed ON-OFF valve, and a thermal throttle to perform the fine control of the mass flow rate. A 1D thermal-fluid model concerning the vapor generation in the tank, and its evolution along the different components is detailed. The thermal throttle model has been experimentally verified using air as a working fluid. The model results agree with the measurements of the verification tests in the hypothesis of the presence of an extended region at the entrance of the pipe where the laminar flow velocity and temperature profiles are not fully developed (known as entry flow region). Finally, the system is experimentally characterized and the model of the full system is calibrated using experimental measurements. The calibration shows that the thermal throttle flow presents an entry flow region, that the viscosity is correctly modeled, and that there is a difference between the measured tank temperature and the effective sublimation temperature.

The electron cooling rate is experimentally investigated along the magnetic lines of a helicon plasma device operating with different magnetic nozzle shapes. Probe measurements in a 2-D region of the plasma plume outline that the polytropic index of electrons has dissimilar values along distinct streamlines ranging from γ_e≃1.4 to γ_e>1.8. Accounting for ionization phenomena as an additional degree of freedom allows to predict a polytropic index smaller than the adiabatic limit. It is observed that a reduced cross-field transport can effectively reduce the electrons degrees of freedom.

A fully cylindrical Hall thruster prototype was tested in the power range of 30–300 W with the objective of understanding the behavior of the discharge as a function of input parameters. Various operating conditions were compared, including two magnetic field configurations, a set of propellant mass flow rates, and a range of discharge voltages. Plasma properties were measured in the plume, with a Langmuir probe, a retarding potential analyzer, and a Faraday cup. The experimental results showed that the mass flow rate strongly affects the ionization and, consequently, other related properties such as the plasma density, currents, and propellant utilization. The discharge voltage also appeared to influence the ion energy and propellant utilization. The performance accessible from the measured magnitudes is assessed, resulting in a maximum thrust efficiency of about 18% at 0.35 mg s−1 and 168 W.