Nicolas Lopez
University of Oxford
A wave near an isolated turning point is typically assumed to have an Airy function profile with respect to the separation distance. This description is incomplete, however, and is insufficient to describe the behavior of more realistic wavefields that are not simple plane waves [1]. Asymptotic matching to a prescribed incoming wavefield generically...
One of the most well-established codes for modeling non-linear Magnetohydrodynamics (MHD) for tokamak reactors is JOREK, which solves these equations with a Beฬzier surface based finite element method. This code produces a highly sparse but also very large linear system. The main solver behind the code uses either GMRES or Bi-CGSTAB with a physics-based preconditioner, but even with the...
Tungsten divertors in tokamaks are designed to withstand and evacuate the excess heat coming from the hot plasma. Some of the tungsten divertor can melt, enter the plasma, and itself become a high-Z impurity plasma. If it enters the core, it can emit enough radiation to cause a loss of thermal plasma energy and degrade or terminate tokamak operation [1]. Thus, it is crucial to develop a...
The role of a runaway current in a post disruption plasma is investigated through numerical simulations in the single helicity limit. Linear results are verified against analytical theory and benchmarked against results already present in the literature. In particular, the presence of a microlayer below the resistive one is confirmed and the effect of the electron inertia on it is also...
Evolving a two-fluid model based on the drift-reduced Braginskii equations [1], GBS [2] is a three-dimensional flux-driven turbulence code designed for simulating plasma turbulence and kinetic neutral dynamics in the tokamak boundary. The GBS simulation domain covers the entire tokamak volume, avoiding the need for an artificial boundary between the core and edge regions, thus preserving the...
To enhance the computational efficiency of particle codes in performing multi-n nonlinear simulations, piecewise finite elements have been developed in tokamak plasma, along with previous work [1,2,3]. Clebsch coordinates are constructed depending on the toroidal domain, which is consistent with the finite difference scheme [1]. In this work, the cubic spline finite element is adopted [3]. The...
This work deals with the relation/interaction between plasma flow and magnetic field during the process of reversed-field pinch (RFP) quasi-helical self-organization [1, 2], featuring improved confinement in the RFX-mod RFP [3].
Experimental [3] and modelling [4] evidence shows that helical self-organization is characterized by quasi-periodical relaxation-reconnection events: partial...
ICRH is an attractive auxiliary heating system for future fusion reactors as it enables direct power deposition to the ions and does not suffer from high density cutoffs. However, ICRH launcher structure needs to be positioned close to the edge plasma to efficiently couple the launched power. This gives rise to enhanced plasma wall interactions near and far from the launching structure. One of...
The gyromoment (GM) approach was developed by B. J. Frei et al. [1] to address the challenges associated with the gyrokinetic (GK) modeling of turbulent dynamics in the boundary region of fusion devices. Based on expanding distribution functions onto a Hermite-Laguerre polynomial basis and evolving in space and time the expansion coefficients, the GM approach has the potential to efficiently...
Ion cyclotron resonance heating (ICRH) is known to create a population of fast ions in fusion plasmas. The non-Maxwellian distribution functions are obtained by solving the Fokker-Planck equation and are needed to describe the radio-frequency wave power deposition and transport phenomena.
This work uses wave fields and power deposition predicted by FEMIC [1], a finite element model for ICRH....
We apply the Physics-informed Neural Networks (PINNs) to the magnetohydrodynamic (MHD) simulations. We build a neural network to find a solution of the MHD equations. We use the coordinate of space-time as model inputs and the outputs of the model are the magnetic field, the plasma bulk velocity, the plasma mass density, and the plasma thermal pressure. The MHD equations are combined into the...
Neoclassical tearing modes (NTM) are metastable magnetic islands in tokamaks; however, they appear frequently in experiments without any noticeable triggering event. In order to understand this, it has been numerically shown that turbulence can create a seed island by mode coupling [1,2,3], even remotely [4] ; such a seed island has been shown in 2D models to further grow from the NTM...
Confinement quality in fusion plasma is significantly influenced by the presence of heavy impurities, e.g. Tungsten, which can lead to radiative heat loss and reduced confinement. This study explores impurity transport modeled by inertial particles in edge plasma, a previously unexamined aspect in plasma physics, using high-resolution direct numerical simulations of the Hasegawa-Wakatani...
The dependence of L-H transition power threshold on plasma density is well documented and captured by the โITPA 2008 scalingโ [1] for high density D plasmas. In view of ITER operations, several studies with different H isotopes resulted in a 1/A mass dependence of the threshold [2]. Of particular interest for ITER H-mode access at low auxiliary power is the existence of a minimum L-H power...
Parametric decay instabilities might play a significant role in various plasma physics phenomena and have garnered considerable interest in recent years [1]. In this study, we compare a model of parametric decay instabilities against the data observed during experiments conducted in the AUG (ASDEX Upgrade) fusion device while performing Electron Cyclotron Wall Conditioning (ECWC)[2].
During...
Integrated modelling for magnetically confined tokamak plasmas is an indispensable tool in interpreting and in guiding the tokamak experiments. To evolve the plasma profiles (current, densities, temperatures), integrated modelling schemes solve a system of stiff diffusion-advection transport equations, constructed using a set of physical models for equilibrium, transport and sources. It is...
P. Costello1
, G. G. Plunk1
, and P. Helander1
1 Max-Planck-Institut fรผr Plasmaphysik, Wendelsteinstraรe 1, 17491 Greifswald, Germany
Since the development of gyrokinetic theory, a myriad of instabilities, which lead to
unwanted turbulent transport in tokamaks and stellarators, have been discovered. A recent
series of publications [1, 2, 3] have introduced a novel approach to computing...
The EC launcher conceptual design is moving towards an engineering design that will satisfy all physics requirements under the various system constraints, including maximum flexibility in case of further refinements of plasma scenarios and tasks [1]. In the current DEMO reference scenario, for the specific magnetic field and plasma density/temperature adopted, the gyrotron frequencies...
Universitร degli Studi Padova - Consorzio RFX
The strong uncertainty related to the estimate of the viscosity coefficient represents an important challenge in the application of magneto-hydrodynamics (MHD) simulation results to laboratory plasmas [1]. This is particularly relevant in the contest of the reversed-field pinch (RFP) configuration, where the viscosity together with the resistivity...
Max Planck Institute for Plasma Physics
Energetic particles will play a central role in future burning plasma experiments, and their
confinement is an important aspect for a fusion reactor. Understanding the effects of energetic
particles (EPs) is essential, as they can strongly interact with the main plasma and drive
magnetohydrodynamic (MHD) instabilities. One notable example is the...
University of Oxford
We investigate the saturation of turbulence in a three-field, fluid model of a magnetised plasma in a Z-pinch magnetic geometry. The model is derived by taking a long-wavelength limit of gyrokinetics and subsequently ordering the electron-temperature-gradient (ETG) to be much larger than all other equilibrium gradients, while still retaining the curvature and...
The particle-in-cell code PICLS is a full-f finite element tool intended to simulate turbulence in the tokamak scrape-off layer using gyrokinetic ions and drift-kinetic electrons. Up until now however, PICLS has been a purely electrostatic code with a prescribed background magnetic field. This approach is not perfectly suited to represent unstable regimes occurring in the scrape-off layer,...
The Divertor Tokamak Test (DTT) [1],[2] is a superconducting device under construction in Frascati, Italy. DTT was proposed to assess the performance of a conventional ITER divertor and address the power exhaust issue that will affect future fusion devices as DEMO. DTT will be equipped with three auxiliary heating systems, including a Neutral Beam Injection (NBI) system. DTT NBI is a...
A linear theory of non local transport in relativistic unmagnetized plasmas is presented. The relativistic effects are due to high electron thermal energy. The relativistic Fokker-Planck equation is analytically solved for perturbed plasmas with respect to the global thermal equilibrium defined by the MaxwellโBoltzmannโJรผttner electron distribution function (EDF). The perturbed EDF is...
The presence of non-axisymmetric perturbations of an axisymmetric toroidal magnetic field results in the chaoticity of the magnetic field lines and strongly affects the charged particle motion and therefore the particle, energy and momentum transport in toroidal plasmas [1-2]. Particle chaoticity is determined by resonance conditions relating the unperturbed Orbital Frequencies of the...
A two-species (one main ion and electrons) fluid model for describing ion temperature gradient (ITG) turbulence in a Z-pinch magnetic geometry has been derived from gyrokinetics. Firstly, we carry out a mass ratio expansion ($\sqrt{m_e/m_i} \ll 1$) similar to the procedure introduced in \cite{Schekochihin_2009}. It is then followed by small $k_{\perp}\rho_i$ expansion, where $k_{\perp}$ is the...
Transport phenomena in fusion plasma devices can be categorized into turbulent and neoclassical parts. Although the primary contribution to particle and heat losses in both tokamaks and optimized stellarators is originates from turbulence, the significance of neoclassical transport theory should not be overlooked. Its applications, for example the prediction of the bootstrap current, are of...
