Axisymmetrical Mhd Equilibrium Solver with Bicubic Hermite Elements

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Advanced tokamak regimes, featuring extended regions of low magnetic shear, are promising candidates for future fusion reactors (record breaking DT pulses at JET in hybrid mode) but are also more prone to specific MHD instabilities. The proximity to a rational surface in a very low shear region weakens field line bending stabilisation and amplifies the effects of toroidal coupling between modes, leading to the emergence of long-wavelength ideal or resistive infernal modes. These modes can grow collectively

Transient phenomena and their control are of high relevance in magnetic confinement fusion plasmas to guarantee a stable and safe plasma operation. Interpretative simulations can maximize the insights gained from experiments on present machines and predictive simulations can help in the preparation of design, mitigation techniques and operational scenarios for future devices. In this article, we provide an overview of recent advances and novel scientific results obtained with the 3D non-linear hybrid fluid-

Nonlinear 3D magnetohydrodynamic (MHD) modeling of shattered pellet injection (SPI) in JET tokamak plasmas is performed with the JOREK code. The study focuses on the validation of simulation result with respect to experimental observations, addressing in particular figures of merit for the efficiency of the SPI, as a technique to mitigate thermal loads by injecting radiative impurities like neon during the thermal quench (TQ) phase of disruptions. A set of JET pulses with neon/deuterium atomic mixture ratio

The Fast Ion Loss Detector (FILD), installed on TCV in 2020 was redesigned and upgraded several times throughout this PhD. The collimator apertures were reduced to increase the energy resolution, a faster CMOS camera was intalled, a novel fast camera (up to 4 MHz) was installed to access microsecond velocity-space mapping, two more slits were added on the bottom partof the FILD head accessing to all magnetic field configurations, a bandpass optical filter was installed to reduce residual light contamination

The first observations of ion cyclotron emission (ICE) in the TCV tokamak are reported. The measured ICE frequency closely follows the deuterium ion cyclotron frequency at the magnetic axis, with temporal variations consistent with equilibrium evolution and associated shifts of the magnetic axis. Core ICE is observed primarily during phases with combined electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI). In most discharges the second harmonic dominates, while in others higher harm

Edge plasma behaviour plays a central role in determining the overall confinement and operational limits of tokamak plasmas. In particular, turbulence at the plasma boundary strongly influences particle and heat transport and remains a key target for performance optimization. Among the shaping strategies currently explored, negative triangularity (NT) operation has emerged as a viable alternative to conventional positive triangularity (PT) plasmas, having demonstrated improved confinement, reduced turbulenc

This work presents numerical and analytic approaches for calculating the amplitude of edge harmonic oscillations (EHOs) associated with Quiescent H-modes in the presence of symmetry breaking magnetic coils. The analytic approach uses a linear ideal MHD model for EHOs and external kink modes subject to a given boundary condition defined by an externally applied helical field. The imposed 3D field is found to extend the parameter space of unstable external kink modes and EHOs, also providing an amplitude for

We present the results of 3D, flux-driven, global, two-fluid electrostatic turbulence simulations in a 5-field period stellarator with an island divertor. The numerical simulations are carried out with the GBS code, which solves the two-fluid drift-reduced Braginskii equations and has been extended recently to simulate plasma turbulence in non-axisymmetric magnetic equilibria. The vacuum magnetic field used in the simulations is carefully constructed using Dommaschk potentials in order to describe a configu

In the tokamak scrape-off layer (SOL) the magnetic field lines are open, channeling particles and heat onto plasma facing components, and constraining their lifetime. Therefore, safe operation of future fusion reactors requires an understanding of SOL plasma dynamics. Recently, we have gained deep insights into the tokamak SOL dynamics by means of massively-parallel fluid electromagnetic turbulence simulations carried out with the Global Braginskii Solver (GBS) code. GBS is currently capable of performing f

We analyze the stochastic initial-boundary value problem for the elastic wave equation with random coefficients and deterministic data. We propose a stochastic collocation method for computing statistical moments of the solution or statistics of some given quantities of interest. We study the convergence rate of the error in the stochastic collocation method. In particular, we show that, the rate of convergence depends on the regularity of the solution or the quantity of interest in the stochastic space, wh

Analysis of magnetic fluctuations is important for understanding the magneto-hydrodynamic (MHD) properties of fusion plasmas. These properties affect nearly all aspects of behaviour of magnetic confinement, and thus are of interest in topics ranging from global plasma stability, control, and disruption avoidance, to more subtle areas such as MHD spectroscopy. Mode number analysis is generally accomplished by interpreting signals from a finite number of Mirnov coils, which typically are unevenly spaced in th

The peakedness of the density profile in source-free MHD-quiescent L-mode plasmas with lower hybrid current drive is observed to decrease with decreasing peaking of the current profile. For the discharges investigated, which include normal and reversed magnetic shear plasmas, the relationship can be summarized as n(e0)/ congruent to 1.2l(i), where l(i) is the normalized internal inductance. Density profiles are monotonically peaked at negative shear. Since density profiles remain peaked at zero loop v

Experiments on the TCV tokamak have shown that rapid vertical movement of diverted ELMy H-mode plasmas can affect the time sequence of edge localized modes. The effect is attributed to the induction of an edge current during the movement of the plasma column in the spatially inhomogeneous vacuum field of a single-null configuration. In TCV the fast vertical movement is provoked by the positional control coils inside the vacuum vessel, however it is argued that a similar effect might be produced in larger de

In noninductively driven discharges, 0.9 MW second harmonic (X2) off-axis co-electron cyclotron current drive deposition is combined with 0.45 MW X2 central heating to create an electron internal transport barrier (eITB) in steady plasma conditions resulting in a 1.6-fold increase of the confinement time (tau(Ee)) over ITER-98L-mode scaling. The eITB is associated with a reversed shear current profile enhanced by a large bootstrap current fraction (up to 80%) and is sustained for up to 10 current redistribu

The low aspect ratio of the mega amp spherical tokamak (MAST) allows differentiation between different forms of the H-mode threshold scaling. With optimized fuelling using inboard puffing, and a connected double null divertor (DND) magnetic configuration, the H-mode power threshold data lie about 1.7 times higher than recent scaling laws. Slight magnetic configuration changes, of the order of the ion Larmor radius, around a connected DND significantly influence H-mode access. H-mode confinement in discharge

The DINA free-boundary equilibrium simulation code has been implemented for TCV, including the full TCV feedback and diagnostic systems. First results showed good agreement with control coil perturbations and correctly reproduced certain non-linear features in the experimental measurements. The latest DINA code simulations, presented in this paper, exploit discharges with different cross-sectional shapes and different vertical instability growth rates which were subjected to controlled vertical displacement

Experimental plasma-edge gradients in JET during the edge-localized-mode (ELM) free H-mode are examined for evidence of the presence and location of the transport barrier region inside the magnetic separatrix. High spatial resolution data in electron density is available in-and outside the separatrix from an Li-beam diagnostic, and in electron temperature inside the separatrix from an ECE diagnostic, while outside the separatrix, a reciprocating probe provides electron density and temperature data in the sc

Ion temperature gradient (ITG) -related instabilities are studied in tokamak-like plasmas with the help of a new global eigenvalue code. Ions are modeled in the frame of gyrokinetic theory so that finite Larmor radius effects of these particles are retained to all orders. Non-adiabatic trapped electron dynamics is taken into account through the bounce-averaged drift kinetic equation. Assuming electrostatic perturbations, the system is closed with the quasineutrality relation. Practical methods are presented

Stability limits for the internal kink mode are calculated for tokamaks with different current profiles and plasma cross-sections using ideal magnetohydrodynamics (MHD). The maximum stable poloidal beta at the q = 1 surface (beta(p)) is sensitive to the current profile, but for circular cross-sections it is typically between 0.1 and 0.2. Large aspect ratio theory gives similar predictions when the appropriate boundary conditions are applied at the plasma-vacuum surface. It is found that the internal kink is

Recent Lower Hybrid Current Drive (LHCD) experiments in TORE SUPRA and JET are reported. Large multijunction launchers have allowed the coupling of 5 MW to the plasma for several seconds with a maximum of 3.8 kw/cm2. Measurements of the scattering matrices of the antennae show good agreement with theory. The current drive efficiency in TORE SUPRA is about 0.2 x 10(20) Am-2/W with LH power alone and reaches 0.4 x 10(20) Am-2/W in JET thanks to a high volume-averaged electron temperature (1.9 keV) and also to

Axisymmetrical Mhd Equilibrium Solver with Bicubic Hermite Elements

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Core MHD instabilities and their spectra in advanced tokamak regimes: ideal and resistive physics

Advances in 3D transient plasma dynamics and control through MHD and hybrid fluid-kinetic simulations with JOREK

Validation of 3d Mhd Simulations of Ne/d2 Mixed Shattered Pellet Injection in Jet

Study of the fast-ion confinement via velocity-space resolved measurements in several plasma scenarios in the TCV tokamak

First observations of ion cyclotron emission in the TCV tokamak

Thermal helium beam measurements of plasma edge turbulence in positive and negative triangularity plasmas on TCV

Extending the Space of Edge Harmonic Oscillations by Magnetic Symmetry Breaking External Coils in Tokamaks

First global simulations of plasma turbulence in a stellarator with an island divertor

Plasma turbulence simulations of the tokamak scrape-off layer

MATHICSE Technical Report : Analysis and computation of the elastic wave equation with random coefficients

Astrophysics and Fusion Plasmas: application of the SparSpec algorithm to the data analysis and design of the ITER high-frequency Mirnov coil diagnostic system

Shear and collisionality dependences of particle pinch in JET L-mode plasmas

Magnetic triggering of ELMs in TCV

Recent results from the electron cyclotron heated plasmas in Tokamak à Configuration Variable (TCV)

Overview of recent experimental results on MAST

Comparing TCV experimental VDE responses with DINA code simulations

Plasma-edge gradients in L-mode and ELM-free H-mode JET plasmas

Global approach to the spectral problem of microinstabilities in tokamak plasmas using a gyrokinetic model

Ideal Mhd Stability of Internal Kinks in Circular and Shaped Tokamaks

Lower Hybrid Current Drive in Tore Supra and Jet