Langmuir probe characterization of a miniature inductively coupled plasma source for ion thrusters

Abstract

Summary form only given. A miniature inductively coupled plasma (ICP) source has been developed. The ICP source is a 1.5cm diameter 5-turn spiral antenna embedded in low temperature co-fired ceramic (LTCC). LTCC has a permittivity of er=7.8. The ICP source operates in a range of 700-900MHz and can strike a plasma from 3-50W at pressures ranging from 50mTorr to 1.75 Torr. The ICP source is now being characterized for use as a plasma generator for a miniature ion thruster. These characterization tests are being conducted for operating conditions comparable to an ion thruster in space, i.e. background pressure of <;10E-6 Torr and a propellant mass flow rate of <;10sccm. A single Langmuir probe is inserted into the plasma approximately 2mm from the antenna, and the voltage is swept from -50 to +50V. The IV curve produced from this voltage sweep is used to estimate the density of the plasma. The results of these experiments will help describe the relationship between the plasma density with RF input power to the ICP source and mass flow rate of propellant. The experiment will be conducted with the ICP source by itself, the ICP source integrated with thruster discharge chamber, and the ICP source with the thruster discharge chamber with a magnetic cusp. Each experiment should show an increase in plasma density compared to the prior experiment. These results will be used to determine the optimum operating condition for an ion thruster by maximizing the mass utilization efficiency and electrical efficiency of the ICP source.