Radial characterization of the electron energy distribution in a helicon source terminated by a double layer

Electron energy probability functions EEPFs are measured across the radius 0 r 6.85 cm of a low pressure 0.3 mTorr helicon plasma source terminated by a current-free double layer. The source field of about 130 G is generated using a Helmholtz coil pair and the radio frequency rf power is maintained at 250 W. All EEPFs exhibit a distribution with a temperature Te bulk out to a break energy break and a relatively depleted distribution for higher energies with a lower temperature Te tail. Te bulk and Te tail are about 8 eV and 5 eV, respectively, for r 4 cm and increase up to about 14 eV and 9 eV near the source wall, i.e., near the rf antenna. break is found to correspond to the potential drop of the double layer for the central part of the source and to the sheath potential near the wall. © 2008 American Institute of Physics. DOI: 10.1063/1.2959137