Impedance Measurement of the Planar Multiring Antenna in the Linear Experimental Advanced Device

The linear experimental advanced device (LEAD) was built at the Southwestern Institute of Physics, aiming to study fundamental plasma physics and serve as a testbed for radio frequency (RF) diagnostics. LEAD equips a helicon plasma source, which adopts a specially designed planar multiring antenna. In order to monitor in real time the antenna impedance, a voltage-current (V–I) probe was developed. First, the results of the antenna impedance measurement by the homemade V–I probe are given. The variations of the antenna impedance with respect to the RF power, magnetic field, and gas flow rate are explored. The antenna impedances measured by the homemade V–I probe are further compared with the commercial V–I suit. These measurements of the antenna impedance could provide essential information to the helicon wave coupling studies in LEAD.

I. Introduction

Helicon plasma has several outstanding features, notably, the high ionization ratio. It could form a high plasma density of up to m⁻³, with only a few tens of kilowatts of external radio frequency (RF) power [1]. Besides, the required confinement magnetic field and the aspect ratio of the device are very flexible, making the helicon a very useful plasma source in various applications, e.g., material surface processing and coating, integrated circuit etching, electrode-free plasma thruster, and wall cleaning in tokamaks. In contrast to numerous small-scale helicon devices [2], [3], [4], [5], [6]; nowadays, coupling to large-volume helicon plasmas has attracted more and more attention in multiple research fields [6], [7], [8], [9].