49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007;
Orlando, Florida
Session BI2: Simulation of Magnetic Fusion Plasmas
9:30 AM–12:30 PM,
Monday, November 12, 2007
Rosen Centre Hotel
Room: Salon 3/4
Chair: William Nevins, Lawrence Livermore National Laboratory
Abstract ID: BAPS.2007.DPP.BI2.2
Abstract: BI2.00002 : Fully 3D RWM and Feedback Stabilization Studies for ITER and AUG*
10:00 AM–10:30 AM
Preview Abstract
Abstract
Author:
Erika Strumberger
(Max-Planck-Institut fuer Plasmaphysik, Garching, Germany)
A high $\beta$-limit is a necessary condition for a working power
plant.
However, instabilities associated with ideal internal and
external modes
limit the plasma beta.
External kink modes of MHD equilibria can be stabilized by a
perfectly
conducting wall sufficiently close to the plasma. In case of a
real wall
with non-zero resistivity the modes become unstable and grow on
the resistive
timescale of magnetic field diffusion through the wall. The
growth rates
of resistive wall modes (RWMs) are typically orders of magnitude
smaller than of
kink modes in the no-wall case so that the stabilization of RWMs
by an
active feedback system becomes feasible.
Some axisymmetric approaches already exist which deal with this
problem numerically.
Nevertheless, because of experimental needs
a realistic external wall has a complex three-dimensional shape.
Usually, it is a
multiply-connected structure. Besides the resistive wall also the
feedback coils violate the axisymmetry of a tokamak
configuration. Therefore,
a three-dimensional, numerical treatment of the feedback
stabilization problem
is necessary.
For this reason, starting from a stellarator code (CAS3D code)
we developed the fully three-dimensional stability code STARWALL,
and the feedback optimization code OPTIM. With these codes, we
are able
to compute the growth rates of resistive wall modes in the presence
of non-axisymmetric, multiply-connected wall structures (i.e.
with holes),
and to model the active
feedback stabilization of these modes.
Analogue to the axisymmetric approaches, the problem is divided
into two parts.
In the open-loop part, the complete
set of eigenvalues and eigenfunctions of the
plasma-resistive-wall system
without feedback currents is determined. Then, in the closed-loop
part an
initial value problem is formulated for the time evolution of the
RWMs and
the currents in the feedback coils. The feedback logics
controlled by a set
of free parameters specifies the interaction between the feedback
currents
and the RWMs. After choosing their values, the effectiveness of
the feedback can
be studied by solving the characteristic equation of the
closed-loop system.
The procedure has been implemented numerically (STARWALL code)
and applied to
resistive wall configurations for ITER and ASDEX Upgrade.
For an optimal choice of the feedback
parameters, the OPTIM code has been developed which optimizes the
stability
of a truncated closed-loop system under variations of the free
parameters.
*EURATOM Association
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.DPP.BI2.2