Eur. Phys. J. D (2017) 71: 134
https://doi.org/10.1140/epjd/e2017-70549-4

Regular Article

Asymmetric frequency dependence of plasma jet formation in resonator electrode

¹ Department of Physics, Pohang University of Science and Technology, 37673 Pohang, Republic of Korea
² Center for Attosecond Science, Max Planck-POSTECH/Korea, 37673 Pohang, Republic of Korea
³ Division of Advanced Nuclear Engineering, Pohang University of Science and Technology, 37673 Pohang, Republic of Korea

^a e-mail: gunsu@postech.ac.kr

Received: 1 September 2016
Received in final form: 15 March 2017
Published online: 25 May 2017

Abstract

Large aspect ratio plasma jets with sub-mm diameter are produced by a microwave coaxial resonator electrode. The jet length shows a sharp asymmetric dependence on the drive frequency: the plasma jet suddenly turns off below a critical frequency while the jet length slowly decreases above the frequency. A general mechanism is proposed to explain the asymmetry based on a universal feedback relation among the plasma impedance, the power coupling efficiency and the plasma dimension in resonator type electrodes. The input impedance of the resonator electrode changes depending on the plasma size formed in the electrode. The degree of the impedance mismatch between the electrode-plasma and the power source determines the power coupling efficiency and the resistive loss in the electrode which in turn affects the plasma size. The asymmetric dependence on the drive frequency is a consequence of the fact that the resonance frequency decreases for increasing plasma size. The feedback model shows a good agreement with the experimental measurements, providing essential information for the plasma control.