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 (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i>–<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i>) probe was developed. First, the results of the antenna impedance measurement by the homemade <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i>–<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i>–<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> probe are further compared with the commercial <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i>–<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> suit. These measurements of the antenna impedance could provide essential information to the helicon wave coupling studies in LEAD.