Publications by Stefano Coda | EPFL Graph Search

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Negative triangularity (NT) plasmas achieve enhanced confinement without edge localized modes nor the need to exceed the L-H heating power threshold. Removing this H-mode accessibility constraint opens a new region of parameter space: scenarios with low external heating power. Using simple zero dimensional power balance and standard empirical scaling laws for confinement, we analyze the impact of external heating on several different reactor-relevant devices (i.e. SPARC, MANTA, ITER and DEMO). We determine

The first divertor was installed in the JET machine between 1992 and 1994 and was operated with carbon tiles and then beryllium tiles in 1994-5. Post-mortem studies after these first experiments demonstrated that most of the impurities deposited in the div ...

Tungsten (W) melting due to transient power loads, for example those delivered by edge localised modes (ELMs), is a major concern for next step fusion devices. A series of experiments has been performed on JET to investigate the dynamics of Type-I ELM-indu ...

This paper details progress in experimental characterisation work at JET for the long-term irradiation station, conducted as part of a project to perform activation experiments using ITER materials. The aim is to take advantage of the significant 14 MeV ne ...

Bursts of turbulence associated with ELMs have been studied systematically in DIII-D with a multichannel phase contrast imaging (PCI) diagnostic, which is sensitive to the long poloidal wavelength components of the density fluctuations in the outer edge of the tokamak. A comparison of the temporal dynamics of the turbulence with the signature D-alpha signal from the divertor has revealed systematic differences between type I and type III ELMs: even though precursor fluctuations are sometimes seen before typ

In tokamaks, plasma shape control is often achieved through a so-called isoflux approach that regulates the poloidal flux differences between a reference point and a set of control points and magnetic field values at suitable locations to obtain the desire ...

Beryllium oxide (BeO) and deuteroxide (BeOxDy) have been found on the melted zone of a beryllium tile extracted from the upper dump plate of JET-ILW (2011-2012 campaign). Results have been obtained using Raman microscopy, which is sensitive to both the che ...

The operating space of the TCV tokamak has been extended to higher elongation, kappa = 2.8, and higher normalized current, I-N = I-p/aB = 3.6MA/mT, than were previously attainable. This has been achieved by optimizing the parameters of the vertical position control system and by optimizing the plasma shape. Experimental current and beta limits were found to be consistent with ideal MHD stability calculations, using measured plasma shapes and profiles. The sawtooth period was measured as a function of elonga

Effect of ELMs on fuel retention at the bulk W target of JET ITER-Like Wall was studied with multi-scale calculations. Plasma input parameters were taken from ELMy H-mode plasma experiment. The energetic intra-ELM fuel particles get implanted and create ne ...

The TCV tokamak (B-T < 1.5 T, R approximate to 0.88 m, a < 0.25 m) has produced a wide variety of plasma configurations, both diverted and limited, with elongations kappa(a), ranging from 0.9 to 2.58, triangularities delta(a) from -0.7 to 1 as well as discharges with nearly rectangular cross sections. Plasma currents of 1 MA have been obtained in elongated discharges (kappa(a) approximate to 2.3). Ohmic discharges with delta(a) < 0 have smaller sawteeth and higher levels of MHD mode activity than plasmas wi

This paper describes the first vertical electron cyclotron emission measurement of non-thermal electron distributions in the Tokamak à Configuration Variable. These measurements were conducted in runaway electron scenarios and in the presence of electron c ...

The identification of the sources of atomic tungsten and the measurement of their radiation distribution in front of all plasma-facing components has been performed in JET with the help of two digital cameras with the same two-dimensional view, equipped wi ...

This work aims at establishing the parameter space for the existence of geodesic acoustic modes (GAMs) on JET as well as investigating their driving and damping mechanisms predicted by different theoretical models. This was achieved using an experimental d ...

Experiments have been carried out on TCV using Electron Cyclotron Resonance Heating (ECRH) actuators to control the plasma current and elongation in real time. In fully non-inductive plasmas, the plasma current may be driven entirely by ECCD on TCV. By replacing the Ohmic coils with the gyrotron power supplies, we were able to control the plasma current in real time. In tokamak plasmas, the elongation is usually controlled by the quadrupole magnetic field from the poloidal field coils. Applying off-axis ECR

The 1-dimensional reaction-diffusion-convection code TOMATOR-1D describes plasma production by RF waves inside a tokamak using the Braginskii continuity and heat balance equations. The model simulates self-consistent radial density and temperature profiles ...

The MHD response and the penetration of a deuterium shattered pellet into a JET plasma is investigated via the non-linear reduced MHD code JOREK with the neutral gas shielding (NGS) ablation model. The dominant MHD destabilizing mechanism by the injection ...

In this work, a Model Predictive Controller (MPC) is proposed to control the plasma shape in the Tokamak à Configuration Variable (TCV). The proposed controller relies on models obtained by coupling linearized plasma response models, derived from the fge code of the Matlab EQuilibrium toolbox (MEQ) suite, with a state-space description of the core TCV magnetic control system. It optimizes the reference signals fed to this inner control loop in order to achieve the desired plasma shape while also enforcing c

In the first results of electron Bernstein wave heating (EBWH) via O-X-B double mode conversion in a medium aspect ratio tokamak performed in TCV, the total power absorption efficiency was typically 60% and the deposition was made off-axis to avoid the central sawteeth perturbation that would prevent a clear detection of the deposition location. Central power deposition is however needed to maximize the global EBWH effects. Therefore, initial experiments have been started to optimize central deposition usin

We report the first experimental observation of the depolarization of the Thomson scattering (TS) radiation, a relativistic effect expected to occur in very high T-e plasmas and never observed so far in a fusion machine. A set of unused optical fibers in t ...

TCV experiments and novel theoretical studies have addressed key questions regarding the operational space of negative triangularity (NT) plasmas in view of an L-mode NT reactor, in terms of stability, performance properties and core-edge integration. We show that reducing the top triangularity (δtop) to more negative values induces an H-L back transition, confirming the direct dependence between H-mode existence and access to 2nd ballooning stability region. We also show that the X-point δ can prohibit H-m

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On the feasibility of Ohmically heated negative triangularity tokamak power plants

Material migration and fuel retention studies during the JET carbon divertor campaigns

Heat flux analysis of Type-I ELM impact on a sloped, protruding surface in the JET bulk tungsten divertor

Activation of ITER materials in JET: nuclear characterisation experiments for the long-term irradiation station

Characterization of density fluctuations during ELMs in the DIII-D tokamak

An interpretable isoflux-based observer for plasma shape control errors in tokamaks

Identification of BeO and BeOxDy in melted zones of the JET Be limiter tiles: Raman study using comparison with laboratory samples

Stability and energy confinement of highly elongated plasmas in TCV

Modelling of the effect of ELMs on fuel retention at the bulk W divertor of JET

Effect of plasma shape on confinement and MHD behaviour in TCV

Cross-calibration and first vertical ECE measurement of electron energy distribution in the TCV tokamak

Determination of tungsten sources in the JET-ILW divertor by spectroscopic imaging in the presence of a strong plasma continuum

Scaling of the geodesic acoustic mode amplitude on JET

Real time plasma current and elongation control using ECRH actuators

RF plasma simulations using the TOMATOR 1D code: a case study for TCV helium ECRH plasmas

3D non-linear MHD simulation of the MHD response and density increase as a result of shattered pellet injection

First Experimental Demonstration of Plasma Shape Control in a Tokamak Through Model Predictive Control

Electron Bernstein Wave Core Deposition via O-X-B Double Mode Conversion in TCV

First observation of the depolarization of Thomson scattering radiation by a fusion plasma

NEGATIVE TRIANGULARITY TOKAMAK OPERATION IN TCV