Partial-depth modulation study of anions and neutrals in low-pressure silane plasmas

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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

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

Electron emission from boundaries is ubiquitous in radio-frequency capacitively coupled plasmas (RF-CCPs) and can exert a significant influence on discharge characteristics. In this work, particle-in-cell Monte-Carlo collisions (PIC-MCC) simulations with an external circuit are performed to investigate a conduction-current-dominated RF-CCP mode, termed the inverted RF-CCP, which is induced by strong boundary electron emission. In this mode, the displacement current becomes negligible, and the conduction cur

Comparative modelling of ITG/TEM turbulence in negative (NT) and positive (PT) triangularity plasma shapes was done using the nonlinear full-f global gyrokinetic particle code JOREK-GK in the realistic X-point tokamak geometry including the Scrape Off Layer (SOL) for TCV and DIII-D parameters. A comparison of JOREK-GK code with the gyrokinetic codes GS2 and GENE was done using NT/PT triangularity TCV L-modes parameters showing good agreement between codes in linear growth rates and clear beneficial effect o

We study the plasmonic and the non-plasmonic regimes of operation of a thin-film amorphous-silicon solar cell. By rigorous calculation, we discuss the impact of the cell geometry on the nature of its optical resonances.

In the search of a fusion reactor using magnetic confinement of toroidal plasmas, many important plasma performance parameters directly depend on the shape of the plasma cross-section. The unique shaping capability of the TCV tokamak ("Tokamak à Configuration Variable") has been exploited to study different aspects of tokamak transport and stability, in which the plasma shape may play a role. This presentation will focus on the effects of plasma shape on transport. The TCV tokamak has produced a host of phy

Microcrystalline hydrogenated silicon films (muc-Si:H) have been deposited by a high current DC plasma in argon-silane-hydrogen mixtures at growth rates up to 10 nm/s and at substrate temperatures below 500 degreesC. Scanning electron microscopy, X-ray diffraction and FTIR analyses show that these films are highly crystallized. The surface morphology depends strongly on the experimental conditions and varies from a cauliflower structure to a prismatic one. The crystalline orientation of the films also chang

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

The helical distortion of a compact tokamak plasma with currents in modular Furth-Hartman type coils is investigated with respect to the impact on the magnetic field structure and to the ideal magnetohydrodynamic stability. A sequence of configurations, in which the current in the helical coils is increased up to the level of that of the main toroidal coils, is generated. The magnetic field structure acquires a ripple along the field lines when the currents in both sets of coils becomes comparable. The magn

Titanium dioxide is a cheap, chemically stable and non-toxic material. However its electrical properties are unstable and it is a modest semiconductor and a mediocre insulator. For several applications it would be interesting to make it either more insulating or more conducting. The goal of this work was to modify the electrical properties of nano-crystalline TiO2 thin films deposited by reactive sputtering and to understand the mechanism leading to these modifications. The principal factors that influence

Within the range of plasma shapes and plasma currents investigated, the electron confinement time, Tau_E increases with density, elongation and negative triangularity (-0.4

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 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

Low aspect ratio tokamaks (LATs) can potentially provide a high ratio of plasma pressure to magnetic pressure beta and high plasma current I at a modest size. This opens up the possibility of a high-power density compact fusion power plant. For the concept to be economically feasible, bootstrap current must be a major component of the plasma current, which requires operating at high beta(p). A high value of the Troyon factor beta(N) and strong shaping is required to allow simultaneous operation at a high-P

The frequency dependence (13.56-70 MHz) of the ion energy distribution at the ground electrode was measured by mass spectrometry in a symmetrical capacitive impedance at very high frequency allows high levels of plasma power and substrate ion flux while maintaining low levels of ion energy and electrode voltage. The lower limit of ion bombardment energy is fixed by the sheath floating potential at high frequency, in contrast to low frequencies where only the radio frequency voltage amplitude is a determinan

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

Stable negative ions containing up to sixteen silicon atoms have been measured by mass spectrometry in RF power-modulated silane plasmas for amorphous silicon deposition. These hydrogenated silicon cluster ions reach much higher masses than the positive ions, which have no more than six silicon atoms. This supports the view that negative ions are the precursors to particulate formation in silane plasmas. The time-dependent fluxes of positive and negative ions from the plasma are shown with a 5 mus time reso

The design and operation of a new vaporizing assembly used for Q-plasma sources are described in this article. The vaporizing system, consisting of two ovens and an effuser, is used to vaporize and direct atoms onto a hot ionizer plate. The hot plate, which may be of tantalum, tungsten, or rhenium, singly ionizes the atoms on contact. The main advantages of this new assembly, compared to previous designs, are the production of higher plasma densities and the control of the radial plasma profile. The heaters

Partial-depth modulation study of anions and neutrals in low-pressure silane plasmas

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

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

Exploring the impedance characteristics in an inverted radio-frequency capacitively coupled plasma discharge due to intense boundary emission

Global gyro-kinetic Ion Temperature Gradient and Trapped Electron Mode turbulence modelling in X-point geometry in negative and positive triangularity

Light-trapping in the near field: the case for plasmonic thin-film solar cells

Physics Insight from Plasma Shaping of TCV Tokamak Plasmas - focus on Electron Heat Transport

Rapid deposition of hydrogenated microcrystalline silicon by a high current DC discharge

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

Effect of helical coils on the magnetic field and the stability of a compact toroidal plasma

Electronic properties of nano-crystalline titanium dioxide thin films

Preliminary Confinement Studies during ECRH in TCV

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

Effect of plasma shape on confinement and MHD behaviour in TCV

Stable equilibria for bootstrap-current-driven low aspect ratio tokamaks

Sheath impedance effects in very high frequency plasma experiments

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

Negative Hydrogenated Silicon Ion Clusters as Particle Precursors in RF Silane Plasma Deposition Experiments

New Vaporizing Assembly for Q-Plasma Sources