53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011;
Salt Lake City, Utah
Session CI2: Pedestal Control With 3D Fields
2:00 PM–5:00 PM,
Monday, November 14, 2011
Room: Ballroom BD
Chair: Jon Menard, Princeton Plasma Physics Laboratory
Abstract ID: BAPS.2011.DPP.CI2.1
Abstract: CI2.00001 : Mitigation of Edge Localized Modes with new active in-vessel saddle coils in ASDEX Upgrade
2:00 PM–2:30 PM
Preview Abstract
Abstract
Author:
Wolfgang Suttrop
(Max-Planck-Institut fuer Plasmaphysik)
One of the challenges for ITER and a fusion reactor is the
potential of severe life-time limitations of the first wall and
divertor due to excessive thermal loads by Edge Localized Modes
(ELMs). While ELMs have been sucessfully mitigated or even
suppressed by application of non-axisymmetric magnetic
perturbations [1], the physics base for this technique is still
sparse and extrapolation towards ITER uncertain. In order to
broaden the experimental data base, ASDEX Upgrade is being
extended with a set of 24 in-vessel saddle coils [2].
A first set of eight in-vessel saddle coils, four coils at the
low field side above and four coils
below midplane, has been operational since the 2011 experimental
campaign, together with a fully tungsten-coated first wall.
This configuration allows for $n=1$ and $n=2$ perturbation fields
with zero or 90 degrees toroidal phase shift between upper and
lower arrays (even or odd parity).
Application of stationary $n=2$ perturbations leads to
mitigation of type-I ELMs in plasmas with moderate to high edge
densities [3]; Greenwald density fraction $n/n_{GW} \geq 0.65$,
and neoclassical pedestal electron collisionalities
$\nu_{\mathrm{e,neo}} \geq 1.2$.
With saddle coils off, the ELMs are of type I, with
stored energy loss per ELM ranging from 30 to 100 kJ,
and peak power loads to the inner divertor of up to $10$~MW
(area-integrated).
With saddle coils (coil current $4.5$~kA$\times$turns),
the frequency of type-I ELMs gradually decreases and eventually
they completely disappear.
In between or instead of these large ELMs intermittent high
frequency transport events are observed, with similarities to
those in small ELM regimes and more continuous power load. The
inner divertor remains completely detached.
Plasma density and stored energy with coils on is not reduced
compared to unmitigated type~I ELM phases.
The tungsten concentration is lower in ELM-mitigated phases than
in unmitigated type~I ELM phases.
Pellets of different size have been injected into an
ELM-mitigated phase; no large ELMs are triggered.
So far, ELM mitigation has been observed with in a wide range
of edge safety factors, $q_{95} = 3.7 - 6.2$.
Direct comparison of optimum resonant and non-resonant fields
(odd and even parity at $q_{95} = 5.5$) shows
no difference of coil current threshold to access the ELM
mitigated regime.
The properties of these discharges are comparable to the high
collisionality regime
in DIII-D [4]. Current experimental work in ASDEX Upgrade aims to
also reproduce
and study the low collisionality ELM suppression regime. \\[4pt]
[1] Editorial, Nucl. Fusion {\bf 49} (2009) 010202 \\[0pt]
[2] SUTTROP, W. et~al, Fusion Eng. Design {\bf 84} (2009)
290, and references therein \\[0pt]
[3] SUTTROP, W. et~al, Phys. Rev. Lett. {\bf 106} (2011)
225004 \\[0pt]
[4] EVANS, T. et~al, Nucl. Fusion {\bf 45} (2005) 595
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DPP.CI2.1