Fast and Automatic Control of a Frequency-Tuned Radiofrequency Plasma Source

Abstract

A frequency-tuned radiofrequency (rf) plasma source is automatically controlled to minimize the rf power reflection and to maintain the constant net rf power corresponding to the forward power minus the reflected power. The experiment is performed with a power amplifier operational for the frequency of 37-43 MHz, a compact helicon source consisting of a loop antenna, a solenoid, and an insulator tube. The rf power is supplied to the rf antenna via an impedance matching circuit consisting of only fixed small ceramic capacitors. It is demonstrated that the reflection coefficient of the rf power is minimized within ∼10 ms, and the net power is successfully maintained at a constant level.

Magnetic Nozzle Radiofrequency Plasma Systems for Space Propulsion, Industry, and Fusion Plasmas

“…Here, the output frequency and power can be quickly and automatically controlled by mounting a controller board on the system, where tiny ceramic capacitors are used for the matching circuit [71]. One of the authors has demonstrated impedance matching within 5 ms and the stabilization of the discharge by maintaining not the output power but the net power, corresponding to the forward reflected powers, at a constant level [73,74]. This system is indeed useful because of the tiny matching circuit for developing the sputtering and etching tools in Minimal Fab.…”

Commentary: On helicon thrusters: Will they ever fly?

“…The suitability criteria also include issues such as the allowed development timeframe and cost, the system's expected lifetime, and potential competitive advantages if successfully developed. There is on-going development work on RF thrusters of different types including the HT and the ICP, which aims at increasing performance and design based on space mission requirements; this includes improved designs of RF antenna, matching network, and RF power control, as shown in recent studies [22][23][24] including Godyak [1].…”

Automatically Controlled Frequency-Tunable rf Plasma Thruster: Ion Beam and Thrust Measurements

“…To overcome the issue on the matching box, several types of the rf generators have adjusted the frequency to match the load impedance to the output impedance of the generator [50][51][52][53], where fixed capacitors are used in the matching circuit. A recently developed fast and automatically controlled rf system has demonstrated the fast impedance matching for the rf plasma source [54], where the source tube is attached to a vacuum flange of a chamber and the rf antenna wound around the source tube is exposed to the atmosphere. On the other hand, the whole structure of the plasma source including the antenna has to be immersed in vacuum for the thruster assessment configuration.…”