Speaker
Saskia Mordijck
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1069.pdf
The role of pinch, fueling in determining the pedestal density structure
S. Mordijck1, R. Groebner2, J. Hughes3, A. Järvinen4, P. Kress1, T. Osborne2, A. Salmi5, T.
Tala5, F. Laggner6, G.R. McKee7, R.A. Moyer8, T. Rhodes9, L. Zeng9
1
The College of William and Mary, Williamsburg, VA, USA
2
General Atomics, San Diego, CA, USA
3
MIT, Cambridge, MA, USA
4
LLNL, Livermore, CA, USA
5
VTT, Helsinki, Finland
6
Princeton University, Princeton, NJ, USA
7
University of Wisconsin – Madison, Madison, WI, USA
8
UCSD, San Diego, CA, USA
9
UCLA, Los Angeles, CA, USA
Experiments were performed on the DIII-D tokamak to examine the impact on H-mode
density pedestal structure to widely varying gas puff rates. At high plasma current and
density, we observe that the ratio of pedestal to separatrix density n e,ped/ne,sep is insensitive to
fueling rate and absolute density. There is a clear shift of the density profile outward into
the SOL and an increase in the separatrix density from 3 to 5x10 19 m-3, accompanied by a
larger precentage increase in the SOL density, from 0.3 – 1.6x10 19 m-3. Though the
increased separatrix density enhances the neutral opacity at the plasma edge, there is no
degradation in the pedestal density height. In addition to increasing the opacity by
increasing the electron density, we added a modulated perturbative gas puff. At the
separatrix we observe a phase shift between the puff modulation and the local n e response,
which decreases with increasing opacity/fueling. Similarly, we find that a reversal in how
the amplitude of the electron density responds to the gas puff modulation in the SOL versus
at the top of the pedestal. In the SOL the amplitude modulation of the electron density
(δne/ne) is strongly reduced from 25% to 5% with increased fueling and n e,sol. At the top of
the pedestal the inverse is observed; at low density and no steady-state gas fueling the
perturbation is nearly negligible (<1%), whereas at high density, the perturbation is close to
4%. Analysis and modelling of this new experimental data will address a longstanding
question: does plasma transport facilitate the density pedestal formation in the regime of
strong neutral screening and reduced pedestal ionization?
This work is supported by the US DOE under DE-SC0007880 1,2, DE-FG02-08ER549842, DE-AC05-
06OR231003, DE-FC02-04ER54698, and DE-SC0014264.
