Spectroscopic diagnostics for liquid lithium divertor studies on the NSTX Page: 4 of 14
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I. INTRODUCTION
The use of lithium coatings evaporated on graphite plasma facing components (PFCs)
has been under investigation for plasma density control and performance improvements in
the National Spherical Torus Experiment (NSTX)"2. Recently, a liquid lithium toroidal
module was installed in the NSTX lower divertor area. The liquid lithium divertor (LLD)
module has a porous molybdenum surface, separated by a stainless steel liner from a copper
substrate. Lithium is deposited on the LLD surface from two overhead evaporators'. A
perceived advantage of the LLD over the solid lithium coating is a self-regenerating lithium
surface for pumping hydrogenic fuel ions and atoms.
In order to assess the relationship between lithium-coated and liquid lithium divertor
surface conditions and edge-core plasma transport and radiation properties, the NSTX di-
agnostics complex has been augmented with a new array of divertor Langmuir probes at the
LLD radial location4 , a material analysis and particle probe, a two color infrared thermog-
raphy system5, and a charge-exchange recombination spectroscopy system6 upgraded for
core lithium density measurements. In this paper we describe two new divertor diagnostics
that are being installed on NSTX: (1) A Lyman-a (Lye) diode array (hereforth referred to
as LADA) for divertor recycling measurements, and (2) A ultraviolet-visible-near infrared
(UV-VIS-NIR) divertor imaging spectrometer (hereforth referred to as DIMS) for divertor
atomic and molecular flux measurements. These diagnostics will contribute to the planned
studies of retention and recycling of deuterium as a function of LLD surface conditions (e.g.,
Li coverage, temperature), divertor Te and ne, strike point proximity and flux expansion,
as well as to relate the LLD surface temperature to the measured influx of impurity and
hydrogenic species.
II. METHOD
Plasma operations with evaporated lithium coatings in NSTX bring up a number of
diagnostic concerns. The concerns include (1) degradation in transmission of diagnostic
port windows and reflectivity of in-vessel mirrors due to exposure to lithium fluxes, (2)
deposition of lithium on exposed diagnostic parts (e.g., foil filters, probe surfaces), and (3)
large changes in the dynamic range of some measured quantities (e.g., edge neutral pressure,2
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Soukhanovskii, V A; Roquemore, A L; Bell, R E; Kaita, R & Kugel, H W. Spectroscopic diagnostics for liquid lithium divertor studies on the NSTX, article, June 4, 2010; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc870807/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.