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CHANGES IN PARTICLE PUMPING DUE TO VARIATION IN
MAGNETIC BALANCE NEAR DOUBLE-NULL IN DIII-DT. W. Petrie, et al.
Changes in Particle Pumping Due to Variation in Magnetic Balance
Near Double-Null in DIII-D
T.W. Petrie1, J.G. Watkins2, S.L. Allen3, N.H. Brooks, M.E. Fenstermacher3,
J.R. Ferronl, C.M. Greenfieldl, M. Groth3, A.W. Hyatt1, T.C. Lucel, M.A. Mahdavil,
M.J. Schafferl, M.R. Wade4, W.P. West1, and the DIII-D Team
1General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
2Sandia National Laboratories, Albuquerque, New Mexico, USA
3Lawrence Livermore National Laboratory, Livermore, California, USA
40ak Ridge National Laboratory, Oak Ridge, Tennessee, USA
Abstract. We report on a recent experiment examining how changes in the divertor
magnetic balance affect the rate that particles can be pumped at the divertor targets. We
find that both the edge density of the core plasma and divertor recycling play important
roles in properly interpreting this pumping result.
Previous studies on DIII-D have identified several important differences between
double-null (DN) and single-null (SN) divertor operation. Small variations in the magnetic
balance near-DN have large effects on both the power- and particle loadings at the divertor
targets [1,2]. These most likely result from an interplay between the plasma geometry and
ion particle drifts [3,4], e.g., "BxVB" and "ExB" drifts [5,6]. Other studies have shown
that changes in magnetic balance affect the core plasma [7] and where ELMs strike the
vessel [8]. In this paper, we examine how variations in the magnetic balance impact the
rate at which particles are removed from the core plasma via pumping.Three examples of the
poloidal cross-sections consid-
ered in this study are shown in
Fig. 1: (a) unbalanced upper
DN, (b) balanced DN, and
(c) unbalanced lower DN. [For
the sake of discussion, we refer
to the shapes in Fig. 1(a,b,c) as
"UDN", "BDN" and "LDN",
respectively.] These plasmas
exhibited type-1 ELMing [9]f
BxVBDome Cryopump
f -Baffle Cryopump
(dRsep =+1.2cm) (dRsep a 0)and high energy confinement, Fig. 1. The three basic equilibria used in this study: (a) DN
i.e., TE/tE89P = (2.1-2.5), where biased toward the upper divertor (dRsep = +1.2 cm), (b) balanced
TE89P is the 1989 L-mode en- DN (dRsep = 0), and (c) DN biased toward the lower divertor
(dRsep = -1.2 cm). The "primary" (heavy) and "secondary"
ergy confinement scaling [10]. (light) divertor separatrices are shown. Characteristic parameters:
Pumping was done from two Ip = 1.2 MA, BT= 1.9 T, and PINJ = 6-11 MW.
poloidal locations. One pump was located inside the "dome" plenum and exhausted
particles near the upper inner divertor target. The second pump was located under the
"baffle" plenum and exhausted particles near the upper outer divertor target. The locationse 0
(dRsep=-1.2 cm)
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Petrie, T. W.; Watkins, J. G.; Allen, S. L.; Brooks, N. H.; Fenstermacher, M. E.; Ferron, J. R. et al. Changes in Particle Pumping Due to Variation in Magnetic Balance Near Double-Null in DIII-D, article, July 1, 2003; United States. (https://digital.library.unt.edu/ark:/67531/metadc733947/m1/4/: accessed July 15, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.