Interaction of neutral atoms and plasma turbulence in the tokamak edge region

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Screening of high-Z (W) impurities from the confined plasma by the temperature gradient at the plasma periphery of fusion-grade H-mode plasmas was demonstrated for the first time in JET with the Be/W wall (Field et al 2023 Nucl. Fusion 63 016028). Additional experiments have been performed in JET during 2023, including in deuterium-tritium (DT) during the DTE3 campaign, to further optimise the impurity screening in such plasmas, as well as our bolometric measurements of the W impurity fluxes between and dur

Simulating turbulence in the tokamak boundary, which is crucial for understanding and optimizing future fusion power plants performance, is computationally challenging due to the complex, multi-physics, and multi-scale nature of plasma dynamics. In the boundary region, plasma interacts with neutral particles recycled from the walls, leading to nonlinear phenomena that control confinement and heat exhaustion. Accurately capturing these coupled processes requires solving large-scale, stiff, and non-local pro

The EC Upper Launcher (UL) and Ex-vessel waveguide (EW) are integral components of the ITER Electron Cyclotron (EC) system [1], which plays a key role in achieving and maintaining the high temperatures required for nuclear fusion within the tokamak, providing plasma heating and current drive, and magnetohydrodynamics (MHD) stabilization, which are crucial for ITER’s operational success. The EC system is increasingly becoming the reference mechanism for plasma heating in both present and future devices. Nota

In this work, we extend our previous studies (Singh et al 2023, Nucl. Fusion 63, 086029; Singh et al 2024, Nucl. Fusion 64, 106005) by performing global δf electromagnetic gyrokinetic simulations including collisions using the ORB5 particle-in-cell (PIC) code, spanning the plasma from magnetic axis to separatrix. The analysis focuses on ion temperature gradient (ITG) and trapped electron mode (TEM) turbulence in both linear and nonlinear regimes for experimentally relevant profiles and parameters of the ADI

This thesis presents a study on the statistical characterization and predictability of plasma discharges in the TCV tokamak, based on time-dependent transport simulations performed with the ASTRA code. The work combines physical modeling, numerical implementation, and nonlinear time-series analysis to bridge the gap between transport simulations and the dynamical complexity of experimentally observed plasma behavior.

Biological pathways have been extensively analyzed and modeled in respect to overall conversions of substrates to products, although information on atom transitions or atom flow in metabolic networks is not available in databases. The reaction atom mapping designates the track of all the atoms from substrates to products in each individual reaction and consequently, it elucidates the mass flow in a pathway of reactions. The study of metabolism at the atomic level is of great importance in many applications

The existence of a critical pressure gradient needed to drive the interchange instability is experimentally demonstrated in the simple magnetized torus TORoidal Plasma EXperiment [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)]. This gradient is reached during a scan in the neutral gas pressure pn. Around a critical value for pn, depending on the magnetic configuration and on the injected rf power, a small increase in the neutral gas pressure triggers a transition in the plasma behavior. The pressure pro

We present applications of a recently developed method, the singular value decomposition inversion (SVD-I), for inverting line integrated multichannel interferometer measurements in fusion devices. The method expands the local electron density profiles into a limited series of orthogonal basis functions formed from the singular value decomposition of Thomson scattering measurements, which are obtained at much lower frequencies than the interferometer data. Because these basis functions are formed from a loc

Localized electron heating and current drive, like those produced by electron cyclotron heating (ECH) systems, are powerful tools for controlling the sawtooth period. They allow the direct modification of the plasma parameters which determine the sawtooth stability. In this paper we report a set of new experimental results obtained in the TokamakConfiguration Variable (TCV) and a set of related simulations obtained applying a sawtooth period model in a transport code. The TCV device, equipped with a very fl

Moderately peaked electron density profiles are observed in virtually all plasma conditions in TCV. The existence of an anomalous pinch is unambiguously demonstrated by the observation of peaked density profiles in stationary, fully relaxed, fully current driven electron cyclotron current drive (ECCD) discharges with V-loop = 0. The behaviour of the density profiles from a database of 300 Ohmic L- and H-mode, as well as electron cyclotron heating and ECCD discharges, is compared to predictions of models bas

Large-scale molecular dynamics of cascade production of the primary damage state are performed in nanocrystalline nickel with an average grain diameter of 12 nm and primary knock-on atom kinetic energies ranging from 5 to 30 keV. The role of the grain boundary during the cascade production of irradiated NC Ni is discussed in terms of grain-boundary structure. It is shown that regions of misfit in the grain boundaries can absorb self-interstitials and that stacking-fault tetrahedra are formed in the neighbou

A characterization of the H-mode in Tokamak de Varennes (TdeV) is presented, combining results obtained from spectroscopic measurements with observations of global plasma parameters. Controlled L- and H-modes are obtained by applying an external bias on the divertor plate and/or by varying the plasma triangularity using similar steady-state discharges with electron cyclotron resonance heating (ECRH). A qualitative study of the impurity emission asymmetries is presented and discussed by proposing a simple mo

Compact optimized stellarators offer novel solutions for confining high-beta plasmas and developing magnetic confinement fusion. The three-dimensional plasma shape can be designed to enhance the magnetohydrodynamic (MHD) stability without feedback or nearby conducting structures and provide drift-orbit confinement similar to tokamaks. These configurations offer the possibility of combining the steady-state low-recirculating power, external control, and disruption resilience of previous stellarators with the

The prediction of the thermal energy confinement time, tau(th), for ITER size experiments is based on power law scalings obtained using data sets of present tokamak results in specific regimes, the most relevant being the ELMy H mode regime. A thorough statistical approach has provided a bust fit to these data with an estimation of the error bars which forms the basis for the ITER EDA design parameters. In this article the range of variation of the main parameters in the database are studied individually an

Fast particle driven instabilities are investigated at low toroidal field B-0 approximate to 1 T in tritium, deuterium and hydrogen plasmas. Tritium, deuterium and hydrogen neutral beams with energies of 160, 140 and 110 keV were injected, respectively, into tritium, deuterium and hydrogen plasmas. The destabilization of Alfven eigenmodes was observed during injection of tritium beams into a tritium plasma and during the injection of deuterium beams into a deuterium plasma but not during the injection of hy

Within the range of plasma shapes and plasma currents investigated, the electron confinement time, tau_Ee, increases with safety factor, density and negative triangularity similar to the Ohmic heating case. There is little dependence of tau_Ee on the heating location provided power deposition occurs inside the q=1 surface; as power deposition moves out of the inversion surface, tau_Ee decreases. The power-induced energy confinement degradation exponent (tau_Ee~PaP) is as usual: alpha_P ~-0.5. As a general t

The linear relativistic theory of electron cyclotron wave propagation predicts partial absorption of the extraordinary mode at the third electron cyclotron harmonic for typical parameters of present day tokamak plasmas. Since the waves are not totally damped, a quantitative confirmation of such predictions is important to establish this particular resonance scheme firmly for plasma heating and current drive. Specific experiments have been performed on Tore Supra, to measure the optical thickness of the thir

Results from the first experiments to drive Alfven Eigenmodes (AEs) with antennas external to a tokamak plasma are presented. In ohmically heated plasma discharges, direct experimental measurements of the damping of toroidicity induced AEs (TAEs) have allowed an identification of different regimes corresponding to different dominant TAE absorption mechanisms with a wide range of damping rates, 10(-3) less than or equal to gamma/omega less than or equal to 10(-1). In plasmas heated by ion cyclotron resonance

Precise control of the shape and position of double-null divertor configurations in the TCV tokamak has been used to trigger reliably the transition from ELM-free to ELMy ohmic H mode and back. Preprogrammed modulation of the magnetic axis height (+/- 1.25 cm), with fixed shaping field, caused the plasma to evolve, during a single discharge, between double-null-upper, double-null and double-null-lower configurations, with the secondary X point remaining close to the separatrix. The transition from ELM-free

Interaction of neutral atoms and plasma turbulence in the tokamak edge region

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Optimised 'hybrid' Scenario H-mode Plasmas for W Radiation Control in Jet with the Be/w Wall

Acceleration of Solvers for Plasma Simulation in the Tokamak Boundary

The design of the EC Upper Launcher and Ex-vessel waveguide systems for ITER

Electromagnetic gyrokinetic simulation of drift wave turbulence in ADITYA-U with collisions

Statistical Analysis of Plasma Discharge Predictability in Transport Simulations of TCV Experiments

Automated reconstruction of E-coli metabolic network from labeled metabolites

Observation of a critical pressure gradient for the stabilization of interchange modes in simple magnetized toroidal plasmas

Application of the singular value decomposition method for inversion of interferometer measurements in fusion plasmas

Effects of localized electron heating and current drive on the sawtooth period

Observation and empirical modelling of the anomalous particle pinch in TCV

Radiation damage near grain boundaries

Characterization of impurities in L- and H-modes created by divertor biasing and plasma triangularity in TdeV

Physics of the compact advanced stellarator NCSX

Considerations on energy confinement time scalings using present tokamak databases and prediction for ITER size experiments

Beam driven Alfven eigenmodes and fishbones in JET

EFFECT OF LOCALISED ELECTRON CYCLOTRON HEATING ON ENERGY CONFINEMENT AND MHD IN TCV

Measurement of the optical depth at the third electron cyclotron harmonic in tore supra

Overview of alfven eigenmode experiments in jet

Elm Control During Double-Null Ohmic H Modes in Tcv