Quad Confinement Thruster produces strange, disjointed acceleration layer

Modern spacecraft are increasingly reliant on plasma-based thrusters for propulsion. These drives produce low levels of thrust but are extremely efficient in terms of propellant consumption. One promising design is the Quad Confinement Thruster (QCT), which uses an array of electric and magnetic fields in multiple orientations to provide precise control over the plasma discharge and thrust.

Lucca Fabris et al. studied a QCT and mapped the velocity of the ions over a variety of magnetic field arrangements. They found an ion acceleration layer disconnected from the plasma source.

“Surprisingly, ion acceleration is happening in a narrow layer detached from the thruster exit plane,” said author Andrea Lucca Fabris. “This finding is profoundly different in comparison with experimental observations in other plasma propulsion technologies, where ions are accelerated in proximity of the thruster exhaust plane.”

The researchers set up their QCT in a vacuum chamber to simulate the environment of space and examined the resulting plasma discharge using laser-induced fluorescence spectroscopy. This method allowed them to non-invasively map the ion velocity at multiple points throughout the plume.

Using this method, they discovered a centimeter-wide acceleration layer, located 8 centimeters downstream from the plasma discharge exit plane. Here, the ions more than triple their velocity. This layer exists through multiple configurations and testing conditions. The researchers propose that this effect is due to the presence of an electrostatic potential drop, although they suggest additional study is needed.

“A deeper understanding of the nature of this layer constitutes an interesting scientific research question that deserves further investigation,” said Lucca Fabris.

Source: “Evidence of a free-space ion acceleration layer in the plume of a quad confinement plasma source,” by Andrea Lucca Fabris, Christopher V. Young, Aaron Knoll, Emmanuelle Rosati Azevedo, and Mark A. Cappelli, Journal of Applied Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0062555 .

This paper is part of the Physics of Electric Propulsion Collection, learn more here .