Characterization and stabilization of an electron-cyclotron resonance plasma source using an automatic microwave tuner

Abstract

An automatic microwave stub tuner (AST) has been developed and used to characterize and stabilize an electron-cyclotron resonance (ECR) plasma source. The tuner provides a new method for measuring plasma impedance dynamically without disturbing the plasma. The Ar ECR plasmas were excited by a 2.45 GHz microwave (<800 W) in the presence of the static axial magnetic fields ranging from 875 to 2000 G, and the characteristics were investigated using a double probe and the AST. Results of these measurements indicated that the Ar ECR plasma had discrete stable modes where the plasma parameters and impedance varied continuously. For certain operating conditions, slight shifts of microwave power and/or magnetic-field strength brought about discontinuous mode transitions. In the transition regions, the drastic changes of plasma characteristics were observed, resulting in the instability of the plasma. It was quite effective for stabilizing the unstable plasmas to control the reflection coefficient of the microwave transmission line.

Experimental study of pulsed ion beam generated by different pulsing topology in 2.45 GHz ECR proton source

“…When the microwave power is applied to the plasma chamber in presence of a magnetic field, the gas ionization and plasma formation processes take place [17]. Once the plasma is formed, impedance matching between the plasma impedance (load impedance) and the microwave generator impedance (source impedance) is necessary for maximum power transfer [18,19]. The plasma impedance is a complex time-varying parameter whereas the source impedance is static.…”

Microwave Frequency Tuning of an ECR Ion Thruster for Impedance Matching

“…Most of ground ECR ion/plasma sources are equipped with a triple-stub tuner in the microwave feed line for impedance matching and are operated at a constant microwave frequency of magnetrons (usually at 2.45 GHz). Some of them are operated using automatic mechanical tuners 2) . On the other hand, JAXA's ECR ion thrusters for spacecraft propulsion eliminate these mechanical tuners because of simplicity, reliability and robustness.…”