We report on the development of unique, high-density helicon plasma sources and describe their applications. Characterization of one of the largest helicon plasma sources yet constructed is made. Scalings of the particle production efficiency are derived from various plasma production devices in open literature and our own data from long and short cylinder devices, i.e., high and low values of the aspect ratio A ͑the ratio of the axial length to the diameter͒, considering the power balance in the framework of a simple diffusion model. A high plasma production efficiency is demonstrated, and we clarify the structures of the excited waves in the low A region down to 0.075 ͑the large device diameter of 73.8 cm with the axial length as short as 5.5 cm͒. We describe the application to plasma propulsion using a new concept that employs no electrodes. A very small diameter ͑2.5 cm͒ helicon plasma with 10 13 cm −3 density is produced, and the preliminary results of electromagnetic plasma acceleration are briefly described.

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