On-axis parallel ion speeds near mechanical and magnetic apertures in a helicon plasma device

Xuan Sun, S. A. Cohen, Earl E. Scime, Mahmood Miah

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Using laser-induced fluorescence, measurements of parallel ion velocities were made along the axis of a helicon-generated Ar plasma column whose radius was modified by spatially separated mechanical and magnetic apertures. Ion acceleration to supersonic speeds was observed 0.1-5 cm downstream of both aperture types, simultaneously generating two steady-state double layers (DLs) when both apertures were in place. The DL downstream of the mechanical aperture plate had a larger potential drop, Δ φDL =6-9 k Te, compared to the DL downstream of the magnetic aperture, Δ φDL ∼3 k Te. In the presheath region upstream of the mechanical aperture, the convective ion speed increased over a collisional distance; from stagnant at 4 cm from the aperture to the 1.4 times the sound speed at the aperture. The dependence of the free- and trapped-ion-velocity-distribution functions on the magnetic-field strength and mechanical-aperture electrical bias are also presented.

Original languageEnglish (US)
Article number103509
Pages (from-to)1-8
Number of pages8
JournalPhysics of Plasmas
Issue number10
StatePublished - 2005

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics


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