620 research outputs found
PB3D: a new code for edge 3-D ideal linear peeling-ballooning stability
A new numerical code PB3D (Peeling-Ballooning in 3-D) is presented. It implements and solves the intermediate-to-high-n ideal linear magnetohydrodynamic stability theory extended to full edge 3-D magnetic toroidal configurations in previous work [1]. The features that make PB3D unique are the assumptions on the perturbation structure through intermediate-to-high mode numbers n in general 3-D configurations, while allowing for displacement of the plasma edge. This makes PB3D capable of very efficient calculations of the full 3-D stability for the output of multiple equilibrium codes. As first verification, it is checked that results from the stability code MISHKA [2], which considers axisymmetric equilibrium configurations, are accurately reproduced, and these are then successfully extended to 3-D configurations, through comparison with COBRA [3], as well as using checks on physical consistency. The non-intuitive 3-D results presented serve as a tentative first proof of the capabilities of the code
Verifying PB3D:a new code for 3D ideal linear peeling-ballooning stability
Magnetic nuclear fusion devices are a promising candidate for the confinement of thermonuclear plasmas but various instabilities set important limits on their operation. Peeling-ballooning perturbations, which can be described appropriately using high-n linear ideal MHD stability theory, are two of them, where high-n indicates that the perturbations are localized along the magnetic field lines [1]. A new numerical code, called PB3D (Peeling Ballooning in 3D) was written to investigate the stability of these instabilities in a fast and reliable way, solving the generalized eigensystem presented first in [8]. The important new aspect of this theory is that it describes stability of full 3-D equilibrium configurations that are allowed to perturb the plasma edge, in contrast with previous treatments such as used in the ELITE [9] or MISHKA code [5] that both treat the stability of axisymmetric equilibria. 3D effects are important for numerous reasons: In tokamaks axisymmetry is often broken, either deliberately, such as when RMP techniques are used to suppress periodic plasma relaxations called ELMs, or due to imperfections in the axisymmetric design, such as the toroidal ripple introduced by discrete toroidal field coils. Stellarators devices, on the other hand, are inherently 3D and cannot be approximated using axisymmetric theory. In this work, the verification of PB3D with stability results for axisymmetric equilibria is presented, indicating that these are accurately reproduced, and non-intuitive first 3-D results are given.</p
PB3D: A new code for edge 3-D ideal linear peeling-ballooning stability
A new numerical code PB3D (Peeling-Ballooning in 3-D) is presented. It implements
and solves the intermediate-to-high-n ideal linear magnetohydrodynamic stability theory
extended to full edge 3-D magnetic toroidal configurations in previous work [1]. The
features that make PB3D unique are the assumptions on the perturbation structure
through intermediate-to-high mode numbers n in general 3-D configurations, while
allowing for displacement of the plasma edge. This makes PB3D capable of very
e cient calculations of the full 3-D stability for the output of multiple equilibrium
codes. As first verification, it is checked that results from the stability code MISHKA [2],
which considers axisymmetric equilibrium configurations, are accurately reproduced,
and these are then successfully extended to 3-D configurations, through comparison
with COBRA [3], as well as using checks on physical consistency. The non-intuitive
3-D results presented serve as a tentative first proof of the capabilities of the code.This research was sponsored in part by DGICYT (DirecciĂłn General de Investigaciones
CientĂficas y TecnolĂłgicas) of Spain under Project No. ENE2015-6826
Enhanced Preconditioner for JOREK MHD Solver
The JOREK extended magneto-hydrodynamic (MHD) code is a widely used
simulation code for studying the non-linear dynamics of large-scale
instabilities in divertor tokamak plasmas. Due to the large scale-separation
intrinsic to these phenomena both in space and time, the computational costs
for simulations in realistic geometry and with realistic parameters can be very
high, motivating the investment of considerable effort for optimization. In
this article, a set of developments regarding the JOREK solver and
preconditioner is described, which lead to overall significant benefits for
large production simulations. This comprises in particular enhanced convergence
in highly non-linear scenarios and a general reduction of memory consumption
and computational costs. The developments include faster construction of
preconditioner matrices, a domain decomposition of preconditioning matrices for
solver libraries that can handle distributed matrices, interfaces for
additional solver libraries, an option to use matrix compression methods, and
the implementation of a complex solver interface for the preconditioner. The
most significant development presented consists in a generalization of the
physics based preconditioner to "mode groups", which allows to account for the
dominant interactions between toroidal Fourier modes in highly non-linear
simulations. At the cost of a moderate increase of memory consumption, the
technique can strongly enhance convergence in suitable cases allowing to use
significantly larger time steps. For all developments, benchmarks based on
typical simulation cases demonstrate the resulting improvements
Understanding the effect resonant magnetic perturbations have on ELMs
All current estimations of the energy released by type I ELMs indicate that,
in order to ensure an adequate lifetime of the divertor targets on ITER, a
mechanism is required to decrease the amount of energy released by an ELM, or
to eliminate ELMs altogether. One such amelioration mechanism relies on
perturbing the magnetic field in the edge plasma region, either leading to more
frequent, smaller ELMs (ELM mitigation) or ELM suppression. This technique of
Resonant Magnetic Perturbations (RMPs) has been employed to suppress type I
ELMs at high collisionality/density on DIII-D, ASDEX Upgrade, KSTAR and JET and
at low collisionality on DIII-D. At ITER-like collisionality the RMPs enhance
the transport of particles or energy and keep the edge pressure gradient below
the 2D linear ideal MHD critical value that would trigger an ELM, whereas at
high collisionality/density the type I ELMs are replaced by small type II ELMs.
Although ELM suppression only occurs within limitied operational ranges, ELM
mitigation is much more easily achieved. The exact parameters that determine
the onset of ELM suppression are unknown but in all cases the magnetic
perturbations produce 3D distortions to the plasma and enhanced particle
transport. The incorporation of these 3D effects in codes will be essential in
order to make quantitative predictions for future devices.Comment: 32 pages, 9 figure
Non-linear Simulations of MHD Instabilities in Tokamaks Including Eddy Current Effects and Perspectives for the Extension to Halo Currents
The dynamics of large scale plasma instabilities can strongly be influenced
by the mutual interaction with currents flowing in conducting vessel
structures. Especially eddy currents caused by time-varying magnetic
perturbations and halo currents flowing directly from the plasma into the walls
are important. The relevance of a resistive wall model is directly evident for
Resistive Wall Modes (RWMs) or Vertical Displacement Events (VDEs). However,
also the linear and non-linear properties of most other large-scale
instabilities may be influenced significantly by the interaction with currents
in conducting structures near the plasma. The understanding of halo currents
arising during disruptions and VDEs, which are a serious concern for ITER as
they may lead to strong asymmetric forces on vessel structures, could also
benefit strongly from these non-linear modeling capabilities. Modeling the
plasma dynamics and its interaction with wall currents requires solving the
magneto-hydrodynamic (MHD) equations in realistic toroidal X-point geometry
consistently coupled with a model for the vacuum region and the resistive
conducting structures. With this in mind, the non-linear finite element MHD
code JOREK has been coupled with the resistive wall code STARWALL, which allows
to include the effects of eddy currents in 3D conducting structures in
non-linear MHD simulations. This article summarizes the capabilities of the
coupled JOREK-STARWALL system and presents benchmark results as well as first
applications to non-linear simulations of RWMs, VDEs, disruptions triggered by
massive gas injection, and Quiescent H-Mode. As an outlook, the perspectives
for extending the model to halo currents are described.Comment: Proceeding paper for Theory of Fusion Plasmas (Joint Varenna-Lausanne
International Workshop), Varenna, Italy (September 1-5, 2014); accepted for
publication in: to Journal of Physics: Conference Serie
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