Publications by Henri Weisen | EPFL Graph Search

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Different types of central relaxation oscillations are observed in the presence of ECH depending on the location of the deposited power. In the TCV tokamak, normal sawteeth, i.e. triangular sawteeth similar to ohmic sawteeth, and saturated sawteeth are observed with central ECH power deposition, while giant sawteeth and 'humpback' oscillations occur when heating close to the sawtooth inversion surface of the local soft X ray emissivity. New measurements with high temporal resolution show that the crash phas

Neutron emission spectroscopy is a diagnostic technique that allows for energy measurements of neutrons born in nuclear reactions. The JET tokamak fusion experiment (Culham, UK) has a special role in this respect as advanced spectrometers for 2.5 MeV and 1 ...

Bayesian integrated data analysis combines measurements from different diagnostics to jointly measure plasma parameters of interest such as temperatures, densities, and drift velocities. Integrated data analysis of fast-ion measurements has long been hampe ...

Simulations of the DD neutron rates predicted by the ASCOT and TRANSP Monte Carlo heating codes for a diverse set of JET-C (JET with carbon plasma facing components) plasmas are compared. A previous study (Weisen et al 2017 Nucl. Fusion 57 076029) of this ...

Confinement in TCV electron cyclotron heated discharges was studied as a function of plasma shape, i.e. as a function of elongation, 1.1 < kappa < 2.15, and triangularity, -0.65 less than or equal to delta less than or equal to 0.55. The electron energy confinement time was found to increase with elongation, owing in part to the increase of plasma current with elongation. The beneficial effect of negative triangularities was most effective at low power and tended to decrease at the higher powers used. The l

Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and their beta limits can be raised by destabilization (modification) of sawteeth by ion cyclotron radio frequency heating (ICRH). Alpha simulation experiments with

The TCV tokamak has obtained ohmic H-modes in virtually all diverted plasmas with the ion del B drift directed towards an X-point and in several elongated limiter plasmas. Troyon factors (beta(tor)aB/l(p)) up to 2 and line average densities up to 2.2 x 10(20) m(-3), corresponding to the Greenwald limit, have been obtained in diverted ELM-free H-modes. Quasi-stationary H-modes lasting for the entire current flat top (1.5 s) have been obtained in the presence of regular ELMs. The occurrence and magnitude of E

Electron temperature, pressure and density profiles from a large variety of ohmically heated plasmas in the TCV tokamak (B-T < 1.5 T, R-0 = 0.88 m, a < 0.25 m) are compared with theoretical predictions based on the assumption that the magnetic entropy is constant in time. These discharges include limited and diverted discharges with elongations in the range 1-2.54, triangularities in the range 0.5-0.72 and plasma currents in the range 0.1-1 MA. Over the entire range of quasi-stationary ohmic conditions it i

Particle transport in magnetized plasmas is investigated with a fluid model of drift wave turbulence. An analytical calculation shows that magnetic field curvature and thermodiffusion drive an anomalous pinch. The curvature driven pinch velocity is consistent with the prediction of turbulence equipartition theory. The thermodiffusion flux is found to be directed inward for a small ratio of electron to ion pressure gradient, and it reverses its sign when increasing this ratio. Numerical simulations confirm t

The extreme shaping capabilities of the TCV tokamak have been used to investigate the effect of plasma geometry on the confinement of non-recycling trace impurities injected by means of the laser blow-off technique. The progression of the injected silicon in the core of TCV Ohmic limiter plasmas was followed by the 200-channel soft x-ray (SXR) photodiode array with good spatial and temporal resolution. The results show that the plasma triangularity and elongation play an important role in the impurity confi

The data of the H alpha high-resolution spectroscopy, collected on the multiple lines of sight, which cover the entire divertor space in poloidal cross-section, during the recent hydrogen-deuterium experiments in JET-ILW (ITER-like wall), are processed. A ...

This paper presents the transport analysis of high density baseline discharges in the 2016 experimental campaign of the Joint European Torus with the ITER-Like Wall (JET-ILW), where a significant increase in the deuterium-deuterium (D-D) fusion neutron rat ...

The design and first results are presented from a bolometric diagnostic with high temporal resolution recently installed on the TCV tokamak. The system consists of two pinhole cameras viewing the plasma from above and below at the same toroidal location. Each camera is equipped with an AXUV-16ELO linear array of 16 p-n junction photodiodes, characterized by a flat spectral sensitivity from ultraviolet to x-ray energies, a high temporal response (< 0.5 mu s), and insensitivity to low-energy neutral particles

A pedestal prediction model Europed is built on the existing EPED1 model by coupling it with core transport simulation using a Bohm-gyroBohm transport model to self-consistently predict JET-ILW power scan for hybrid plasmas that display weaker power degrad ...

The measurement of the energy spectra and densities of alpha-particles and other fast ions are part of the ITER measurement requirements, highlighting the importance of energy-resolved energetic-particle measurements for the mission of ITER. However, it ha ...

The EUROfusion Work Package JET3 programme, established to enable the technological exploitation of the JET experiments over the next years, includes, within the NEXP subproject, a novel Shutdown Dose Rate (SDR) experiment. Considering its ITER-relevance, ...

Operation of the JET tokamak with beryllium and tungsten ITER-like wall provides unique opportunity for detailed studies on dust generation: quantity, morphology, location, etc. The programme carried out in response to ITER needs for safety assessment comp ...

In the preparation for the Deuterium-Tritium campaign, JET will operate with a tritium plasma. The T + T reaction consists of two notable channels: (1) T + T -> He-4 + 2n, (2) T + T -> He-5 + n -> He-4 + 2n. The reaction channel (1) is the reaction with th ...

The TCV tokamak (R = 0.88 in, a < 0.25 in, BT < 1.54 T) is equipped with six 0.5 MW gyrotron sources operating at 82.7 GHz for second harmonic X mode ECH. By distributing the ECCD current sources over the discharge cross section, fully driven stationary plasmas with I-p = 210 kA, n(e0) = 2 x 10(19) m(-3), T-e0 approximate to 4 keV, were obtained for the full discharge duration of 2 s. Highly peaked electron temperature profiles with T-e0 up to 12 keV were obtained in central counter-current drive scenarios

A theoretical model for isotopologues of beryllium monohydride, BeH, BeD and BeT, A (2)Pi to X (2)Sigma(+) visible and X (2)Sigma(+) to X (2)Sigma(+) infrared rovibronic spectra is presented. The MARVEL procedure is used to compute empirical rovibronic ene ...

Henri Weisen

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Understanding sawtooth activity during intense electron cyclotron heating experiments on TCV

Neutron emission spectroscopy of D plasmas at JET with a compact liquid scintillating neutron spectrometer

Bayesian Integrated Data Analysis of Fast-Ion Measurements by Velocity-Space Tomography

Comparison of JET-C DD neutron rates independently predicted by the ASCOT and TRANSP Monte Carlo heating codes

Energy confinement and MHD activity in shaped TCV plasmas with localized electron cyclotron heating

Overview of JET results

Ohmic H-modes in the TCV tokamak

Stationary magnetic entropy in ohmic tokamak plasmas: Experimental evidence from the TCV device

Turbulent particle transport in magnetized plasmas

Effects of plasma shape on laser blow-off injected impurity transport in TCV

Determination of isotope ratio in the divertor of JET-ILW by high-resolution H alpha spectroscopy: H-D experiment and implications for D-T experiment

High fusion performance at high T-i/T-e in JET-ILW baseline plasmas with high NBI heating power and low gas puffing

Fast bolometric measurements on the TCV tokamak

Integrated modelling of H-mode pedestal and confinement in JET-ILW

Diagnostic of fast-ion energy spectra and densities in magnetized plasmas

Shutdown dose rate measurements after the 2016 Deuterium-Deuterium campaign at JET

Dust generation in tokamaks: Overview of beryllium and tungsten dust characterisation in JET with the ITER-like wall

Activation material selection for multiple foil activation detectors in JET TT campaign

Overview of TCV results

Synthetic spectra of BeH, BeD and BeT for emission modeling in JET plasmas