Hydrogen ion beam generated by a current-free double layer in a helicon plasma

摘要

A current-free double layer in an expanding hydrogen helicon discharge (13.56 MHz) has been discovered by measuring a beam of hydrogen ions at the low potential side of the double layer. The ion beam is supersonic (～2.1c_s) and is detected using a retarding field energy analyzer positioned downstream of the double layer for pressures below a few mTorr and for radio frequency powers up to 1800 W.