Speaker
Dan M. Thomas
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1021.pdf
Understanding tungsten divertor sourcing, SOL transport, and its impact
on core impurity accumulation in DIII-D high performance discharges *
D.M. Thomas1, T. Abrams1, J. Barton2, J.A. Boedo3, A.R. Briesemeister4, D. Buchenhauer2, I.
Bykov3, C.P. Chrobak1, R. Ding5, D. Donovan6, J.D. Elder7, B.A. Grierson8, H.Y Guo1, J.
Guterl4, E.M Hollmann3, C.J. Lasnier9, A.W. Leonard1, M.A. Makowski9, A.G. McLean9, R.
Nygren2, T.W. Petrie1, D.L. Rudakov3, P.C. Stangeby7, E.A. Unterberg4, B. Victor9, W.R.
Wampler2, H.Q. Wang4, J.G. Watkins2, M. Zach4
1
General Atomics, General Atomics, San Diego, CA, USA
2
Sandia National Laboratory, Albuquerque, NM, USA
3
University of California San Diego, San Diego, CA, USA
4
Oak Ridge National Laboratory, Oak Ridge, TN, USA
5
Oak Ridge Associated Universities, Oak Ridge, TN, USA
6
University of Tennessee, Knoxville, TN, USA
7
University of Toronto, Toronto, ON, Canada
8
Princeton Plasma Physics Laboratory, Princeton, NJ, USA
9
Lawrence Livermore National Laboratory, Livermore, CA, USA
The DIII-D metal rings campaign demonstrated the ability to run high performance plasmas
with tungsten at the outer divertor strike point and provided detailed information on W sourcing
and transport from the divertor in a mixed material environment. Using two isotopically distinct
toroidal rings of W-coated metal inserts, advanced tokamak (AT) discharges (PAUX=14 MW,
H98 =1.5-1.6, βN =3.6-3.7) show performance similar to all-C divertor discharges, with low
core W concentrations (few 10-5) for the case of central ECH and rapid ELMs (fELM~200 Hz).
W impurities transported to the midplane, measured by collector probes inserted in the far SOL,
predominantly originate from the outer strike point (OSP) region rather than from a W source
positioned in the far SOL. Conversely, for discharges with larger, less frequent ELMs (fELM~60
Hz) the W impurities are shown to transport equally from the OSP and far-SOL regions. Direct
measurement of gross W sputtering shows peak source rates during Type-I ELMs of 1-2x10E16
/cm2/s, many times the inter-ELM rate (1-2x 10E15 /cm2/s). Detailed analysis shows that C
impurity and D fuel ions contribute equally to W divertor sourcing during ELMs, in contrast to
the JET-ILW where D ions are the main contributor, or to the inter-ELM case on DIII-D where
C dominates the W sputtering. In addition, ELM-resolved measurements of W sourcing for
differing BT directions reveal the peak W erosion rate during large ELMs shifts radially due to
a combination of drift effects and ELM wetted area. For L-mode experiments, OEDGE
modeling suggests that measured asymmetries in the collected W may be explained by a W
buildup in the SOL at the crown of the plasma, driven by the parallel grad-Ti force.
__________________________
*
This work was performed in part under the auspices of the U.S. Department of Energy by General Atomics
under DE-FC02-04ER54698, DE-FG02-07ER54917, DE-AC05-00OR22725, DE-AC04-94AL85000, DE-AC02-
09CH11466, DE-AC52-07N27344, and DE-AC05-00OR23100.
