The results of a study of the mode transitions in the helicon source when used in the geometry required for plasma processing are presented. We find that the basic characteristics of high density (>5×1011cm−3in the processing chamber at 500 W) and low plasma potential (∼15 V) are observed in this configuration. The mode transitions can be interpreted in terms of the dispersion relation for the helicon wave. A study of the initial plasma breakdown has also been made and the results have aided in the understanding of the operation of the helicon source during pulsed plasma etching.