scholarly journals On the polarization of shear Alfvén and acoustic continuous spectra in toroidal plasmas

2020 ◽  
Vol 86 (5) ◽  
Author(s):  
M. V. Falessi ◽  
N. Carlevaro ◽  
V. Fusco ◽  
E. Giovannozzi ◽  
P. Lauber ◽  
...  
Keyword(s):  
Fusion Plasmas ◽  
Toroidal Plasmas ◽  
Divertor Tokamak ◽  
Plasma Compression ◽  
Ideal Magnetohydrodynamics ◽  
Toroidal Geometry ◽  
The Ideal

In this work, the FALCON code is adopted for illustrating the features of shear Alfvén and sound continuous spectra in toroidal fusion plasmas. The FALCON codes employ the local Floquet analysis discussed in (Phys. Plasmas, vol. 26, issue 8, 2019, 082502) for computing global structures of continuous spectra in general toroidal geometry. As particular applications, reference equilibria for the divertor tokamak test and ASDEX Upgrade plasmas are considered. In particular, we illustrate the importance of mode polarization for recognizing the physical relevance of the various branches of the continuous spectra in the ideal magnetohydrodynamics limit. We also analyse the effect of plasma compression and the validity of the slow sound approximation.

scholarly journals Physics-guided machine learning approaches to predict the ideal stability properties of fusion plasmas

2020 ◽  
Vol 60 (4) ◽  
pp. 046033 ◽  
Author(s):  
A. Piccione ◽  
J.W. Berkery ◽  
S.A. Sabbagh ◽  
Y. Andreopoulos
Keyword(s):  
Machine Learning ◽  
Fusion Plasmas ◽  
Learning Approaches ◽  
Stability Properties ◽  
The Ideal

An Efficient Implementation of the Divergence Free Constraint in a Discontinuous Galerkin Method for Magnetohydrodynamics on Unstructured Meshes

2017 ◽  
Vol 21 (2) ◽  
pp. 423-442 ◽  
Author(s):  
Christian Klingenberg ◽  
Frank Pörner ◽  
Yinhua Xia
Keyword(s):  
Magnetic Field ◽  
Discontinuous Galerkin ◽  
Discontinuous Galerkin Method ◽  
Efficient Method ◽  
Numerical Experiments ◽  
Unstructured Meshes ◽  
Mhd Equations ◽  
Ideal Magnetohydrodynamics ◽  
Divergence Free ◽  
The Ideal

AbstractIn this paper we consider a discontinuous Galerkin discretization of the ideal magnetohydrodynamics (MHD) equations on unstructured meshes, and the divergence free constraint (∇·B=0) of its magnetic field B. We first present two approaches for maintaining the divergence free constraint, namely the approach of a locally divergence free projection inspired by locally divergence free elements [19], and another approach of the divergence cleaning technique given by Dedner et al. [15]. By combining these two approaches we obtain a efficient method at the almost same numerical cost. Finally, numerical experiments are performed to show the capacity and efficiency of the scheme.

scholarly journals Regular and non-regular solutions of the Riemann problem in ideal magnetohydrodynamics

2012 ◽  
Vol 79 (3) ◽  
pp. 335-356 ◽  
Author(s):  
K. TAKAHASHI ◽  
S. YAMADA
Keyword(s):  
Numerical Simulations ◽  
Riemann Problem ◽  
Regular Solution ◽  
Initial Condition ◽  
Regular Solutions ◽  
Arbitrary Initial Condition ◽  
Standard Problem ◽  
Ideal Mhd ◽  
Ideal Magnetohydrodynamics ◽  
The Ideal

AbstractWe have built a code to numerically solve the Riemann problem in ideal magnetohydrodynamics (MHD) for an arbitrary initial condition to investigate a variety of solutions more thoroughly. The code can handle not only regular solutions, in which no intermediate shocks are involved, but also all types of non-regular solutions if any. As a first application, we explored the neighborhood of the initial condition that was first picked up by Brio and Wu (1988) (Brio, M. and Wu, C. C. 1988 An upwind differencing scheme for the equation of ideal magnetohydrodynamics. J. Comput. Phys. 75, 400–422) and has been frequently employed in the literature as a standard problem to validate numerical codes. Contrary to the conventional wisdom that there will always be a regular solution, we found an initial condition for which there is no regular solution but a non-regular one. The latter solution has only regular solutions in its neighborhood and actually sits on the boundary of regular solutions. This implies that the regular solutions are not sufficient to solve the ideal MHD Riemann problem and suggests that at least some types of non-regular solutions are physical. We also demonstrate that the non-regular solutions are not unique. In fact, we found for the Brio and Wu initial condition that there are uncountably many non-regular solutions. This poses an intriguing question: Why a particular non-regular solution is always obtained in numerical simulations? This has important ramifications to the discussion of which intermediate shocks are really admissible.

scholarly journals Cosmic magnetic fields with masclet: an application to galaxy clusters

2020 ◽  
Vol 494 (2) ◽  
pp. 2706-2717
Author(s):  
Vicent Quilis ◽  
José-María Martí ◽  
Susana Planelles
Keyword(s):  
Magnetic Field ◽  
Galaxy Clusters ◽  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Pure Compression ◽  
Ideal Magnetohydrodynamics ◽  
Relative Errors ◽  
Cluster Values ◽  
The Magnetic Field ◽  
The Ideal

ABSTRACT We describe and test a new version of the adaptive mesh refinement cosmological code masclet. The new version of the code includes all the ingredients of its previous version plus a description of the evolution of the magnetic field under the approximation of the ideal magnetohydrodynamics (MHD). To preserve the divergence-free condition of MHD, the original divergence cleaning algorithm of Dedner et al. (2002) is implemented. We present a set of well-known 1D and 2D tests, such as several shock tube problems, the fast rotor, and the Orszag–Tang vortex. The performance of the code in all the tests is excellent with estimated median relative errors of ∇ · B in the 2D tests smaller than 5 × 10−5 for the fast rotor test, and 5 × 10−3 for the Orszag–Tang vortex. As an astrophysical application of the code, we present a simulation of a cosmological box of 40 comoving Mpc side length in which a primordial uniform comoving magnetic field of strength 0.1 nG is seeded. The simulation shows how the magnetic field is channelled along the filaments of gas and is concentrated and amplified within galaxy clusters. Comparison with the values expected from pure compression reveals an additional amplification of the magnetic field caused by turbulence in the central region of the cluster. Values of the order of ∼1µG are obtained in clusters at z ∼ 0 with median relative errors of ∇ · B below 0.4 per cent. The implications of a proper description of the dynamics of the magnetic field and their possible observational counterparts in future facilities are discussed.

scholarly journals Benchmarking 2D against 3D FDTD codes for the assessment of the measurement performance of a low field side plasma position reflectometer applicable to IDTT

2022 ◽  
Vol 17 (01) ◽  
pp. C01017
Author(s):  
F. da Silva ◽  
E. Ricardo ◽  
J. Ferreira ◽  
J. Santos ◽  
S. Heuraux ◽  
...  
Keyword(s):  
High Performance ◽  
Three Dimensional ◽  
Test Facility ◽  
Fusion Plasmas ◽  
Full Wave ◽  
Low Field ◽  
Plasma Position ◽  
Divertor Tokamak ◽  
Difference Time ◽  
Performance Computing

Abstract O-mode reflectometry, a technique to diagnose fusion plasmas, is foreseen as a source of real-time (RT) plasma position and shape measurements for control purposes in the coming generation of machines such as DEMO. It is, thus, of paramount importance to predict the behavior and capabilities of these new reflectometry systems using synthetic diagnostics. Finite-difference time-domain (FDTD) time-dependent codes allow for a comprehensive description of reflectometry but are computationally demanding, especially when it comes to three-dimensional (3D) simulations, which requires access to High Performance Computing (HPC) facilities, making the use of two-dimensional (2D) codes much more common. It is important to understand the compromises made when using a 2D model in order to decide if it is applicable or if a 3D approach is required. This work attempts to answer this question by comparing simulations of a potential plasma position reflectometer (PPR) at the Low Field-Side (LFS) on the Italian Divertor Tokamak Test facility (IDTT) carried out using two full-wave FDTD codes, REFMULF (2D) and REFMUL3 (3D). In particular, the simulations consider one of IDTT’s foreseen plasma scenarios, namely, a Single Null (SN) configuration, at the Start Of Flat-top (SOF) of the plasma current.

Sign in / Sign up

Export Citation Format

Share Document