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Abstract: PSFC/RR-03-06
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In-Situ Gas Conductance and Flow Measurements Through Alcator C-Mod
Divertor Structures With and Without Plasma Present
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B. LaBombard and C. Boswell |
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A specialized arrangement of gas-puff capillaries and in-situ pressure
gauges has been installed in Alcator C-Mod to allow gas conductances
and flows around divertor structures to be measured with or without
plasma present in the chamber. Results are presented from a series of
dedicated experiments performed during the 1020725 run day (MP#313,
"Instrumented Divertor Leakage Experiments"). Gas conductances and flows
are compiled in this report with the aim of providing good benchmark
points for numerical simulations of gas flow and "plasma plugging" physics
in Alcator C-Mod. A strong plasma plugging effect is found at locations
where the divertor structure is opened for diagnostics access (the so-called
"open-port" locations), as evidenced by a factor of ~4 reduction in
the local gas conductance with plasma present. The effect is most dramatic
for locations in the upper chamber region where there is no neutral
baffle structure; a factor of ~5 reduction in the local gas conductance
is found there. Gas conductance through an open divertor flap is measured
to be a factor of ~3 lower than that which has been commonly assumed
using the area of the open flap. The conductance through the flap is
found to be similar with or without plasma present, indicating that
there is no "plasma plugging" effect occurring at this location. The
gas flow rate through a flap that is adjacent to an "open-port" location
is found to be a factor of 2 lower than at a location distant from open
ports. The latter result suggests that significant toroidal variations
in the pressures exist under the lower divertor modules. |
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| 9/11/03 |
Full text:
PDF (42 pages, 2.6 MB) |