title: Upstream ionization instability associated with a current-free double layer.
abstract: A low frequency instability has been observed using various electrostatic probes in a low-pressure expanding helicon plasma. The instability is associated with the presence of a current-free double layer (DL). The frequency of the instability increases linearly with the potential drop of the DL, and simultaneous measurements show their coexistence. A theory for an upstream ionization instability has been developed, which shows that electrons accelerated through the DL increase the ionization upstream and are responsible for the observed instability. The theory is in good agreement with the experimental results.
authors.affiliation: SP3, Research School of Physical Sciences and Engineering, The Australian National University, Australian Capital Territory 0200, Australia. ane.aanesland@anu.edu.au
authors.forename: A
authors.initials: A
authors.lastname: Aanesland
authors.forename: C
authors.initials: C
authors.lastname: Charles
authors.forename: M A
authors.initials: MA
authors.lastname: Lieberman
authors.forename: R W
authors.initials: RW
authors.lastname: Boswell