Experimental Diagnostics for Electrons and Atoms in Low Pressure Iodine Plasmas

Iodine has been studied by several groups as a propellant for spacecraft electric propulsion devices as an alternative

to replace xenon, which is expensive, scarce, and requires compressed gas handling. The physics of electronegative

plasmas, such as iodine plasmas, has a much less extensive literature, as compared to electropositive plasmas. In this work, spatially resolved optical and electrostatic diagnostics are developed and implemented on PEGASES thruster, used as an ICP ion source without any magnetic field nor acceleration stage. Effects of pressure are studied over a large range (0.5 mTorr – 30 mTorr) with a discharge power around 200W. Langmuir probe measurements yield the electron density and the electron temperature. In order to measure the temperature of I, two optical diagnostics have been implemented. Laser absorption spectroscopy at 7603 cm^-1 yield the temperature and the absolute density of the fundamental state while laser absorption spectroscopy at 11036 cm^-1 leads to the temperature of an atomic excited state. Even at very low pressure, temperatures are much hotter than with in argon plasmas meaning that creation processes of I atoms are very energetic.