56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014;
New Orleans, Louisiana
Session GI1: Runaways, Divertors, and Edge Physics
9:30 AM–12:30 PM,
Tuesday, October 28, 2014
Room: Acadia
Chair: Glen Wurden, Los Alamos National Laboratory
Abstract ID: BAPS.2014.DPP.GI1.3
Abstract: GI1.00003 : Broadening of the divertor heat flux footprint with increasing number of ELM filaments in NSTX*
10:30 AM–11:00 AM
Preview Abstract
Abstract
Author:
Joon-Wook Ahn
(Oak Ridge National Laboratory)
We report on the broadening (narrowing) of the ELM heat flux footprint with increasing (decreasing) number of filamentary striations from in-depth thermography measurements in NSTX. Edge localized modes (ELMs) represent a challenge to future fusion devices, due to the high heat fluxes on plasma facing surfaces. One ameliorating factor has been that the divertor heat flux characteristic profile width ($\lambda_{\mathrm{q}})$ has been
observed to broaden with the size of ELM, as compared with the inter-ELM $\lambda_{\mathrm{q}}$, which keeps the peak heat flux (q$_{\mathrm{peak}})$ from increasing.\footnote{T. Eich \textit{et al}., J. Nucl. Mater. \textbf{415}, S856 (2011)}$^,$\footnote{S. Devaux \textit{et al}., J. Nucl. Mater. \textbf{415}, S865 (2011)} In contrast, $\lambda_{\mathrm{q}}$ has been observed to narrow during ELMs under certain conditions in NSTX, for both naturally occurring\footnote{J-W. Ahn \textit{et al}., J. Nucl. Mater. \textbf{438}, S317 (2013)} and
3-D fields triggered\footnote{J-W. Ahn \textit{et al}., Plasma Phys. Control. Fusion \textbf{56}, 015005
(2014)} ELMs. Fast thermographic measurements and detailed analysis demonstrate that the ELM $\lambda_{\mathrm{q}}$ increases with the number of observed filamentary striations, $i.e.,$ profile
narrowing (broadening) occurs when the number of striations is smaller (larger) than 3-4.\footnote{J-W. Ahn \textit{et al}., submitted to Phys. Rev. Lett. (2014)} With profile narrowing,\footnote{Ahn, J. Nucl. Mater (2013)} q$_{\mathrm{peak}}$ at ELM peak times is inversely related (proportional) to $\lambda_{\mathrm{q}}$ (the ELM size), exacerbating the heat flux problem. Edge stability analysis shows\footnote{D.P. Boyle \textit{et al}., Plasma Phys. Control. Fusion \textbf{53}, 105011 (2011)} that NSTX ELMs almost always lie on the current-driven kink/peeling mode side with low toroidal mode number (n$=$1-5), consistent with the typical numbers of striations in NSTX (0-8); in comparison 10-15 striations are normally observed in intermediate-n peeling-ballooning ELMs, e.g., from JET.\footnote{Devaux, J. Nucl. Mater (2011)} The NSTX characteristics may translate directly to ITER, which is also projected to lie on the low-n kink/peeling stability boundary.\footnote{P.B. Snyder \textit{et al}., Nucl. Fusion \textbf{51}, 103016 (2011)}
*This work was supported by the U.S. DOE, contract DE-AC05-00OR22725 (ORNL) and DE-AC02-09CH11466 (PPPL).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.DPP.GI1.3