Low-power inductively coupled plasma (ICP) electrothermal thrusters have possible applications in satellite propulsion due to their long lifetime and sustainable, impurity-free plasmas. Aiding in the comprehension of the plasma and fluid characteristics of these thrusters, Takayasu Fujino and Mioko Yamauchi studied their performance and power loss using molecular hydrodynamics (MHD) simulations.

“ICP electrochemical thrusters can potentially be used as thrusters for atmospheric-breathing electric propulsion systems in low Earth orbits, because they can use chemically aggressive gases, such as atomic oxygen and molecular oxygen, as propellants,” Fujino said.

Their findings suggest thermal conduction plays an important role in ICP energy loss to the flow channel wall. This leads to a considerably large wall heat loss of over 90% of the input power, creating a hot centerline within the induction coil that cools significantly in the radial direction. The plasma flow is also in a thermal nonequilibrium state with variations in ionization degree and electrical conductivity, which the authors note is an important effect to consider in future simulations.

To validate the transport properties derived from their MHD techniques, Fujino and Yamauchi created an experimental ICP electrothermal model consisting of a hollow-tube flow channel and a radio frequency induction coil, with plasma discharge occurring through a convergent-divergent nozzle. They measured thrust in the experimental system using a relationship between thrust force and applied voltage.

Despite the large wall heat loss and some discrepancy between the simulations and experimental data, the present work provides a good starting point as a rough prediction of ICP thruster performance.

“To be able to implement the proposed low-power ICP electrothermal thrusters in spacecraft and satellites, a substantial improvement in thrust performance is required,” said Fujino.

Source: “Numerical study of plasma-fluid characteristics and thrust performance of a low-power argon inductively coupled plasma electrothermal thruster,” by Takayasu Fujino and Mioko Yamauchi, Journal of Applied Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0022018.