Validating THz time-domain spectroscopy as a tool for characterizing low pressure inductively coupled plasmas of ion thrusters

• DOI: 10.1007/s44205-025-00106-4
• Publication Date: 2025-02-25T10:40:42Z
• Authors: Kalle Bräumer; Rodrigo Sandoval ...; Markus Stein; Konstantin Keil; Kristof Holste; Felix Becker; Jana Zorn; Konrad Wehkamp; Sangam Chatterjee; Peter J. Klar

Abstract Accurate characterization of plasmas within the discharge chambers of gridded ion engines is essential for their advancement. This study showcases the effectivity of terahertz time-domain spectroscopy (THz-TDS) as a non-invasive technique for profiling low-pressure inductively coupled plasmas, mimicking the conditions of the discharge chamber in a radio-frequency ion thruster. Operating at pressures of 3 -

$$7\cdot 10^{-3}$$

7 ·

10

- 3

mbar inside the discharge chamber and a supply power of the radio frequency generator ranging from 10 - 80 W, THz-TDS reveals electron densities in the range of

$$2\cdot 10^{16}$$

2 ·

10 16

-

$$2\cdot 10^{17}$$

2 ·

10 17

m

$$^{-3}$$

- 3

for xenon, krypton, and argon plasmas. Our results show good agreement with Langmuir probe measurements and global plasma modeling, highlighting the accuracy and reliability of THz-TDS. This validation, conducted under conditions representative of gridded ion engines, demonstrates that THz-TDS is, in principle, suitable for characterizing the electron system of the plasma ignited in such thrusters in operation. This offers great potential of developing a promising additional tool for plasma diagnostics in electric propulsion systems.