NDLI: Fast and slow ion populations in expanding helicon plasma observed by laser induced fluorescence tomography

Content Provider	IEEE Xplore Digital Library
Author	Biloiu, I.A. Scime, E.E.
Copyright Year	2008
Description	Author affiliation: Phys. Dept., West Virginia Univ., Morgantown, WV (Biloiu, I.A.; Scime, E.E.)
Abstract	Summary form only given. Since first reports, the current-free electric double layer (EDL) that spontaneously forms at the end of a helicon plasma source, in a region of divergent magnetic field and for pressures below a threshold value, has attracted considerable of interest due to its potential application as a plasma thruster. The measurable parameter of interest in studies of EDL physics is the ion velocity (energy) distribution function (ivdf). One method for obtaining ivdf in plasma is laser induced fluorescence (LIF). However, classical LIF can provide only one-dimensional information since the obtained ivdf is the projection of the 3D ivdf on the laser propagation direction kL. By rotating kL and employing filtered backprojection, the complete 2D ion velocity space distribution function can be acquired via optical tomography. Two dimensional ivdfs were obtained with an internal, scanning LIF probe employing the 3 level Aril LIF scheme $3d'^{2}G_{9/2rarr}4p'^{2}F_{7/2rarr}4s'2D_{5/2}.$ To detect the fast ion population accelerated by passing through the potential drop of the EDL, measurements were taken in the divergent magnetic field region, 19 cm downstream from the helicon source-diffusion chamber junction. It has been found that below a certain value of the magnetic field in the expansion region, the ivdfs change their character: from unimodal to bimodal, showing an almost isotropic slow ion population and a fast ion population. The shape of the fast ion distribution is skewed and distorted. The distortion is a clear signature of the magnetic field divergence. Furthermore, as the helicon source/diffusion chamber magnetic field ratio is increased, the location of the fast group ion population shifts toward higher axial speeds values. A maximum axial speed of ~10.7 km/s, ~2.8 $c_{s}$ (ion sound speed), has been obtained for a magnetic field ratio of 43. The slow ion population location in velocity space is not affected by the change in the magnetic field ratio.
Starting Page	1
Ending Page	1
File Size	63619
Page Count	1
File Format	PDF
ISBN	9781424419296
ISSN	07309244
DOI	10.1109/PLASMA.2008.4591154
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2008-06-15
Publisher Place	Germany
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Physics Laser theory Fluorescence Tomography Plasmas
Content Type	Text
Resource Type	Article
Subject	Atomic and Molecular Physics, and Optics Condensed Matter Physics Electrical and Electronic Engineering

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