Gilles Courret
University of Applied Sciences of Western Switzerland, 1400, Switzerland
Title: High-Power Short-pulsed Microwave Impingement on a High-Pressure Plasma Ball in Acoustic Spherical Resonance
Biography
Biography: Gilles Courret
Abstract
In a project on the development of a pulsed microwave sulfur lamp prototype of 1 kW, we discovered a phenomenon in which the plasma forms a ball at the center of the electrodeless spherical bulb despite gravity. In a preceding publication, we then reported measurements performed with a photodiode that show the high pressure plasma response to short pulses, and showed by modelization that the ball formation results from an acoustic resonance in a spherical mode. With our setup, so using a bulb with 15.6 cm3 volume, this phenomenon appears mostly at a pulse repetition frequency a little below 30 kHz. In this paper, we present complementary results obtained with a second photodiode placed opposite to the first, targeting the side of the ball where the high-power pulse microwaves impinge on the plasma. The second signal is similar to the preceding in the main characteristics: when the resonance occurs, its modulation passes from quasi-triangular to sinusoidal form with a frequency decrease of a few percent, as the oscillation slows down a little below the pulse repetition frequency. The resulting beat also shows up at a frequency equal to the frequency shift. However, the second signal shows an additional rectangular modulation that matches the pulses. The present work focuses on this new revelation and its interpretation.