Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

LE CONFINEMENT INERTIEL PAR LASER, UNE APPROCHE DE LA FUSION THERMONUCLEAIRE CONTROLÉE

On décrit les principes essentiels du confinement par laser, l'intérêt expérimental et théorique du sujet, les efforts entrepris sur ce thème et les résultats obtenus par la communauté internationale concernée

Description d'une expérience de résonance nucléaire sensible à des champs transversaux continus

We describe an experiment on a Nuclear Magnetic Resonance Gyroscope of the type already described by Republic Aviation Corporation, with enhanced sensitivity through " prepolarisation ". Theoretical predictions, from Bloch's equations in low magnetic fields, shows that we may expect many resonances corresponding to one or more electromagnetic quanta. Each of these resonances gives a nonsinusoidal signal and we detect the second harmonic of this signal. With this apparatus we have been able to attain a sensitivity better than 1 mG for transverse magnetic fields.Nous avons repris le principe d'un gyromètre à résonance nucléaire étudié par la Republic Aviation Corp [1] en augmentant la sensibilité par pré-polarisation. L'étude théorique, effectuée à partir des équations de Bloch en champ faible indique l'existence de résonances mettant en jeu un ou plusieurs quanta du champ radiofréquence. Chacune de ces résonances donne lieu à un signal périodique riche en harmoniques ce qui en permet la détection sur l'harmonique 2. L'expérience confirme que ce dispositif constitue un magnétomètre de champs transversaux dont la sensibilité est meilleure que 1 mG

EFFECT OF ELECTRIC FIELDS ON AUTOIONIZING RESONANCES

No abstract availabl

Developing high performance RF heating scenarios on the WEST tokamak

International audienceHigh power experiments, up to 9.2 MW with LHCD and ICRH, have been carried out in the full tungsten tokamak WEST. Quasi non inductive discharges have been achieved allowing to extend the plasma duration to 53s at medium density (ne=3.7×10 19 m-3). Apart few pulses post-boronization, the plasma radiation is rather high (Prad/Ptot~50%) and is dominated by W. This fraction does not vary as the RF power is ramped up and, against expectations, it is quite similar in ICRH and/or LHCD heated plasmas. Hot L mode plasmas (Te(0)>3keV) with a confinement time following the ITER L96 scaling are routinely obtained, confirming the weak aspect ratio dependence of this scaling law. Tungsten accumulation is generally not an operational issue on WEST. Nonetheless, 25% of the of the discharges are affected by a rapid collapse of the central electron temperature which occurs when a slight decrease of Te leads to enhanced radiation causing flat or hollow current profiles. To this respect LHCD-only discharges are compared to ICRH and ICRH/LHCD discharges

Developing high performance RF heating scenarios on the WEST tokamak

International audienceHigh power experiments, up to 9.2 MW with LHCD and ICRH, have been carried out in the full tungsten tokamak WEST. Quasi non inductive discharges have been achieved allowing to extend the plasma duration to 53s at medium density (ne=3.7×10 19 m-3). Apart few pulses post-boronization, the plasma radiation is rather high (Prad/Ptot~50%) and is dominated by W. This fraction does not vary as the RF power is ramped up and, against expectations, it is quite similar in ICRH and/or LHCD heated plasmas. Hot L mode plasmas (Te(0)>3keV) with a confinement time following the ITER L96 scaling are routinely obtained, confirming the weak aspect ratio dependence of this scaling law. Tungsten accumulation is generally not an operational issue on WEST. Nonetheless, 25% of the of the discharges are affected by a rapid collapse of the central electron temperature which occurs when a slight decrease of Te leads to enhanced radiation causing flat or hollow current profiles. To this respect LHCD-only discharges are compared to ICRH and ICRH/LHCD discharges

REVIEW OF X-RAY LASER RESEARCH AT CEL-V

Nous présentons l'état actuel des travaux relatifs au laser X réalisés avec le laser Octal. Les résultats récents concernant les inversions de populations pouvant conduire à une amplification sont rapportés. La théorie et les modèles impliqués dans les schémas d'inversion seront examinés.We present the status of X-ray laser experiments using the Octal laser facility. Recent results dealing with population inversion towards X-ray amplification are reported. Theory and modelling of the involved schemes will also be discussed