Investigation of Flow Separation Control by Nanosecond Pulsed Dielectric Barrier Discharge Actuators

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

Understanding how platform surge motion influences wake dynamics and downstream power availability of floating offshore wind turbines is essential for improving offshore wind energy efficiency. Previous studies have primarily focused on uniform inflow conditions, leaving the frequency-dependent wake behavior in a realistic atmospheric boundary layer unexplored. This study performs high-fidelity, GPU-accelerated large-eddy simulations of a NREL 5 MW reference turbine in an atmospheric boundary layer to inves

This work refers to the development, commissioning, and testing of a control algorithm to optimize the electron cyclotron resonance heating (ECRH) power injection in the Tokamak á configuration variable (TCV). The aim is to understand how the injected microwave polarization, set by corrugated mirrors in the waveguide, influences relevant plasma parameters, namely, electron temperature and stray radiation. To accomplish this task, real-time polarization control is required; therefore, a proportional-integral

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

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

Nuclear fusion reactors offer a promising approach to clean energy production. The design of a tokamak reactor employs external magnetic fields to confine a plasma in a toroidal shape, while external heating mechanisms bring it to thermonuclear conditions. Effective control of plasma temperature, density, and magnetic topology is crucial and requires high-performance systems. Central to this control is the plasma control system, which demands a comprehensive, methodical design and deployment plan before rea

Existing inverter designs are not well-suited for use with high-speed generators due to the IGBTs used as switching elements, which are not fast enough. SiC FETs offer a lower switching time compared to IGBTs, which is key to working with high-frequency machines. However, getting a faster inverter is not as simple as replacing IGBTs with SiC FETs. The system must be adapted, and every component from the gate drivers to the control circuitry, including the sensing elements and power supply must be evaluated

The tokamak periphery determines the fuelling of a tokamak as the result of a complex interplay of neutral and plasma dynamics, perpendicular turbulent transport, and losses to the vessel walls. In the present work, results from first-principles numerical simulations are used in order to study the tokamak fuelling, aiming to assess the neutral penetration length, the ionization region, and the mechanisms that regulate plasma transport in the edge and Scrape-Off Layer (SOL) regions of a tokamak. Ultimately,

In the present work we address the physical mechanisms determining the SOL width of a simple inner-wall limited (IWL) configuration. This seemingly simple configuration has important implications for ITER start-up plasmas, and has triggered an important ITPA-sponsored effort. In the past few years, we have developed a thorough computational and analytical understanding of the physical processes regulating the IWL-SOL width. Our investigations are aided by 3D global, flux driven simulations of SOL turbulence

In this study, human exposure to close-range wireless power transfer (WPT) systems operating in the frequency range 0.1-10 MHz with coil diameters up to 150 mm are investigated. Approximation formulae, which include scaling factors derived from numerical simulations that take variations of complex human anatomies into consideration, are proposed to conservatively estimate human exposure with respect to the most authoritative exposure guidelines. The approximation has been verified for two precommercial prot

Turbulence and bias-induced flows in simple magnetized toroidal plasmas are explored with global three-dimensional fluid simulations, focusing on the parameters of the Helimak experiment. The simulations show that plasma turbulence and transport in the regime of interest are dominated by the ideal interchange instability. The application of a bias voltage alters the structure of the plasma potential, resulting in the equilibrium sheared flows. These bias-induced vertical flows located in the gradient region

For the first time, a rigorous definition of the magnetic presheath entrance (MPSE) is provided, as the location where the drift-reduced approximation breaks down. We consider a weakly collisional electrostatic plasma with cold ions in contact with an absorbing wall in the presence of ExB drifts. We provide expressions at the MPSE for the parallel ion and electron velocities, the gradients of plasma density and potential, and the vorticity. In particular, we show that the plasma potential with respect to th

A new definition of the sheath edge is rigorously derived taking into account the kinetic properties of the plasma, and a consistent set of local sheath edge conditions is presented for the case of a magnetic field perpendicular to the wall. These local boundary conditions give explicit expressions for the ion velocity, the electron velocity, and the electron heat flux at the sheath edge, which can be easily implemented in a fluid code. It is shown that in the case of positive current to the wall, the commo

Starting from a standard single null X-point configuration, a second order null divertor (snowflake (SF)) has been successfully created on the Tokamak a Configuration Variable (TCV) tokamak. The magnetic properties of this innovative configuration have been analysed and compared with a standard X-point configuration. For the SF divertor, the connection length and the flux expansion close to the separatrix exceed those of the standard X-point by more than a factor of 2. The magnetic shear in the plasma edge

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

This report presents a new method to confront the Blind Audio Source Separation (BASS) problem, by means of audio and visual information. In a given mixture, we are able to locate the video sources first and, posteriorly, recover each source signal, only with one microphone and the associated video. The proposed model is based on the Matching Pursuit (MP) [18] decomposition of both audio and video signals into meaningful structures. Frequency components are extracted from the soundtrack, with the consequent

Plasma enhanced chemical vapour deposition (PECVD) of thin films such as amorphous silicon has widespread applications especially in the field of photovoltaic solar cells and thin-film transistors for flat screen production. Industrial applications require high depositions rates over large areas with a good uniformity in layer thickness. In this thesis, some aspects of PECVD in large surface, industrial type, capacitive radio frequency reactor are investigated. The aim of this work is to study the plasma pr

The Retarding Field Analyser (REA) is essentially the only practical tool for the measurement of ion energies parallel to the total magnetic field in the tokamak scrape-off layer plasma. One such device has recently been successfully employed at JET [1]. Its bi-directional nature allows both measurements of ion temperature and plasma flow velocities. The latter are computed by collecting the ion saturation flux to negatively biased entrance slit plates which are set back inside a boron nitride protective ho

L-mode to H-mode transitions (LH transitions) are obtained in a wide range of plasma parameters in TCV Ohmic discharges. LH transitions either occur directly, indicated by a single abrupt drop in D-alpha emission, or present an intermediate 'dithering' phase before the H-mode state is attained, in which D-alpha emission shows rapid excursions between L-mode and H-mode levels. The type of transition, with or without a dithering phase, depends on the plasma current and plasma triangularity. It is less sensiti

Accurate online monitoring of biomass is an enduring problem. Of the various methods available, one of the more satisfactory is with dielec. spectroscopy (often referred to as capacitance monitoring). However, as this technique measures total -biovolume', large changes in cellular morphol. or population distribution will alter the calibration with respect to cell wt. or no. In an attempt to minimize this problem, the full dielec. spectrum was scanned every 10-20 min, and then multivariate techniques were us

Transport phenomena in tokamak plasmas strongly limit the particle and energy confinement and represent a crucial obstacle to controlled thermonuclear fusion. Within the vast framework of transport studies, three topics have been tackled in the present thesis: first, the computation of neoclassical transport coefficients for general axisymmetric equilibria and arbitrary collisionality regime; second, the analysis of the electron temperature behaviour and transport modelling of plasma discharges in the Tokam

Investigation of Flow Separation Control by Nanosecond Pulsed Dielectric Barrier Discharge Actuators

Chat with Graph Search

Effect of the surge motion on wake characteristics of a floating offshore wind turbine

Design and Commissioning of Control Algorithms for Optimal ECRH Power Injection in TCV’s Plasma

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

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

A Simulink-based platform for model-based design and deployment of controllers for tokamak nuclear fusion devices

Design of an inverter for high-speed synchronous generators using SiC FETs

Numerical simulations of plasma fuelling in tokamaks using the GBS code

Theory framework for scrape-off layer turbulence in limited tokamaks

Human Exposure to Close-Range Resonant Wireless Power Transfer Systems as a Function of Design Parameters

Turbulence and bias-induced flows in simple magnetized toroidal plasmas

Boundary conditions for plasma fluid models at the magnetic presheath entrance

Sheath boundary conditions for plasma fluid models

Snowflake Divertor Plasmas on TCV

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

Blind Audio-Visual Source Separation Using Sparse Redundant Representations

Study of radio-frequency plasma deposition of amorphous silicon for the improvement of solar cell production

Particle-in-cell simulations of the impact of retarding field analyser probe head geometry on ion saturation current measurements

Synchronization of L-mode to H-mode transitions on the sawtooth cycle in Ohmic TCV plasmas

On-line biomass monitoring with scanning dielectric spectroscopy

Modelling of electron transport and of sawtooth activity in tokamaks