Abstract
It has been known since Langmuir’s pioneering work with plasma discharges
in the 20’s that one characteristic medium like behavior of the
plasma state of matter is electrostatic shielding of external potentials by
the formation of a ‘sheath’, wherever the plasma comes into contact with
a material boundary. Langmuir first referred to the sheath as the very
thin space charge layer in between the boundary and the bulk plasma,
serving to the keep the plasma neutral. Later, the Langmuir-Bohm fluid
theory of sheath formation held that ions must break the ion sound barrier
in order for charge neutrality to broken and for the sheath to appear,
which is the so-called Bohm Criterion. This was circa 1950. The first
experimental tests of the theory however are only a little more than 10
years old. These involved the use of laser-induced fluorescence (LIF) for
nonperturbing ion dynamics measurements in the plasma state of matter.
Theory agreed with experiment in some respects, but troublingly, not in
others. The beginnings of a resolution, involving another plasma medium
like behavior–streaming instabilities–will be described. The resolution has
gotten the authors muddled with disputes over the nature scientific validity,
disputes which have played out in the pages of Physical Review
Letters. Good and bad career moves will be described.
speaker link: http://www.sandiego.edu/~severn
work funded by National Science Foundation under the Grant Nos. CBET-0903832 and
CBET-0903783
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