Radio frequency matching for helicon plasma sources

A theoretical and experimental study of the matching network linking the antenna of a helicon plasma system to its rf power source is described. It is shown that the introduction or a rf step-down transformer into the conventional L-section network has a number of benefits. The transformer increases the reflected antenna impedance seen by the network, bringing it closer to the output resistance of the rf source. The resulting low-e network is shown to be insensitive to changes in the antenna impedance and the values of the matching elements. It is found that in general only one component in this broad-band network needs to be adjusted father than the iterative adjustment of two components in the conventional network. The importance of this simplification with respect to the automatic control of the matching network is discussed. (C) 1996 American Vacuum Society.