Modeling of DIII-D noble gas puff and pump experiments Page: 4 of 6
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neon and argon, as determined by fits to the
6.5 Neon influ 89873 pumping decay after impurity injection is ter-
Gas pu 80 T /s D2 fuelling minated.
(rt) recy (midplane)
ELM = 55 Hz Global particle balance
Previous analysis of DIII-D impurity
fueling and exhaust experiments has shown
that up to 90% of injected neon may be tem-
porarily stored in the wall . The impurity
particle balance for recycling impurities has
0.3 - --.- previously been analyzed in terms of multi-
reservoir models with charactereristic time
constants . The calculated core efflux from
the MIST ELM model is the driving source in
a global balance that describes the inventory
Neon of the noble gas impurities. The efflux of par-
efflux ticles from the SOL from MIST serves as the
influx for the divertor, plenum, and pump
-6.0 Neon injection reservoirs. In addition, the measured neon
0.0 1.45 pumping speed (which depends on the deuteri-
Time (s) um plenum pressure) is used to fix the pump-
Fig. 3. Core efflux from MIST-ELM model for puff- ing speed in the reservoir model. Figure 3
pump case shot 89873 shows a typical balance as calculated from the
detailed ELM model. The calculation assumes
time constants 'SOL-divertor = 0.7 s, tdiv-baffle= tbaffle-div = 0.1 s, and pump = 0.04 s.
The neon pumping speed in DIII-D has been found to depend on D2 plenum pressure  ,
thus this calculation suggests a possible nonlinear dependence of the neon pumping rate on
ELM-induced peaks in D2 plenum pressure.
Divertor enrichment (MIST b2.5)
The divertor impurity concentration was not directly measured in these experiments,
but the partial pressures of neon and argon in the baffle plenum were measured, so enrich-
ment is described in terms of those values. The relation between divertor and plenum has
been studied with a modified version of the b2 code [developed by B. Braams, 5]. The code
has been run in 5- (helium), 13- (neon) and 21-species (argon) versions. A detailed model for
sheath reflection of energetic impurity neutrals is included. Radial diffusivities are the same
as the edge values for the MIST modeling for these discharges: DA = 0.7 m2/s, and Vpinch
= 0. The ADPAK atomic physics package is included for neon/argon comparisons, and the
STRAHL database is used for helium/neon comparisons. In addition, a description of the par-
ticle sources from divertor plate recycling, midplane and divertor deuterium puffing, divertor
impurity puffing, and back-conductance of deuterium and impurities from the DIII-D plenum
is included. These sources strongly complicate the conventional 1-D (parallel) picture of the
balance between friction and ion temperature gradient forces, since there is a localized source
of back-conducted D2 (and impurities) on the outboard side of the outer strike point, near the
floor. For a typical measured D2 plenum pressure of 4 mTorr, and neon partial pressure of
0.04 mTorr, there are estimated 100 Torr L/s and 1 Torr L/s back flows for D2 and neon,
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Hogan, J.T.; Wade, M.; Maingi, R.; Owen, L.; Schaffer, M. & West, P. Modeling of DIII-D noble gas puff and pump experiments, article, August 1, 1997; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc694031/m1/4/: accessed May 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.