56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014;
New Orleans, Louisiana
Session JI1: ITER Physics
2:00 PM–5:00 PM,
Tuesday, October 28, 2014
Room: Acadia
Chair: Chuck Greenfield, General Atomics
Abstract ID: BAPS.2014.DPP.JI1.1
Abstract: JI1.00001 : Narrow limiter SOL power channels and their impact on ITER first wall shaping
2:00 PM–2:30 PM
Preview Abstract
Abstract
Author:
Martin Kocan
(ITER Organization)
Until recently, it was generally accepted that the profile of parallel heat
flux density in the SOL of limited tokamak plasmas can be well approximated
by a single exponential with decay length $\lambda_{\mathrm{q}}$. This
popular belief was emphatically shown to be erroneous in 2012, when IR
measurements on the inner column of JET limiter discharges revealed the
presence of a narrow heat flux channel adjacent to the last closed flux
surface, resembling a feature seen elsewhere two decades ago, but never
seriously pursued by the edge physics community. This near-SOL decay occurs
with $\lambda_{\mathrm{q}}$ few mm, much shorter than the main SOL
$\lambda_{\mathrm{q}}$, and can raise the heat flux at the limiter apex a
factor 1-4 above the value expected from a single, broad exponential. The
JET observations were of great practical consequence, demonstrating that the
logarithmically-shaped ITER inner wall (IW), foreseen as a limiter surface
for plasma start-up, would be unsuited to handling the power loads produced
by such a narrow feature. Alerted by this JET data, the ITER Organization
(IO) initiated a multi-machine effort to examine this new physics, with the
C-Mod, DIII-D, COMPASS and TCV tokamaks all finding the narrow heat flux
channel in dedicated experiments. This talk will describe how these new data
are helping to unravel the physics of the narrow feature and how they have
provided a strong enough basis for the IO to modify the IW toroidal shape
profile. The new IW shape is optimized for a double-exponential profile with
$\lambda_{\mathrm{q}} = $ 4 and 50 mm, both derived from multi-machine
databases for the near and main-SOL features. It has the interesting
property of mitigating the impact of the narrow feature, whilst paying no
penalty if the latter is not eventually found in ITER. If it were, and
without the modification, IWL limiter operation up to several MA, as
required by the ITER Heat Load Specifications, would not be possible.
The views and opinions expressed herein do not necessarily reflect those of
the ITER Organization.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.DPP.JI1.1