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

Off-Resonance Nutation Nuclear-Magnetic-Resonance Study of Framework Aluminosilicate Glasses with Li, Na, K, Rb or Cs as Charge-Balancing Cation

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Al-27 Nuclear-Magnetic-Resonance Study of Synthetic and Natural Corundum (Alpha-Al2o3) - Some Experimental Aspects of Quantitative Al-27 Nuclear-Magnetic-Resonance Spectroscopy

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Shallow angle x-ray diffraction from in-situ silica:titania sol-gel thin films

X-ray diffraction at shallow angles of incidence has been used to examine three silica:titania sol-gel thin films. Comparison with transmission x-ray diffraction measurements of similar materials in the bulk shows a distinct increase in disorder in the silica network. An increase in porosity of the network in thin films is also likely, suggested by an increase in Si-O-H bonds. No differences in structure between samples with differing titania contents were observed using this technique

Solid-State Mas NMR-Study of Pentameric Aluminosilicate Groups wiht 180-Degrees Intertetrahedral AL-O-SI Angles in Zunyite and Harderite

The minerals zunyite, AL(13)Si(5)O(20)(OH,F)(18)Cl, and harkerite, Ca24Mg8[AlSi4(O,OH)(16)](2)- (CO3)(8)(BO3)(8)(H2O,Cl), have been studied by means of solid-state Al-27 MAS NMR. Zunyite contains Si5O16 pentamers and harkerite contains AlSi4(O,OH)(16) pentamers. These pentameric groups are unique because their T-O-Si angles are almost 180 degrees. Chemical analysis of the zunyite sample shows that it has excess Al: the A-Si ratio is 2.9, compared with the ideal of 2.6. High-speed spinning Al-27 MAS NMR spectra (11-13 kHz) showed two more signals than the spectra obtained by Kunwar et al. (1984). The signal with delta(iso) = 46.8 +/- 0.5 ppm represents the excess Al, which enters the central Si1 site of the Si5O16 pentamer. This assumption is confirmed by the fact that delta(iso) of Al in the AlSi4(O,OH)(16) pentamer in harkerite is 44 +/- 1 ppm. Additional proof comes from comparing the electrostatic energy and the quadrupole interaction of Al in either a Si1 or Si2 configuration. The Al site in the pentamers of zunyite and harkerite can be considered as a q(4)(4Si) site. In this case, Al-O-Si angles are correlated with the Al-27 chemical shift (Lippmaa et al., 1986). This correlation holds well for the Al-27 data for harkerite. The value for zunyite indicates that the structure adapts to the incorporation of Al in the Si1 site by a narrowing of the A1-O-Si angle to 171 +/- 2.5 degrees. The lower limit of the chemical shift range for Al in framework aluminosilicates is decreased by 12 ppm, from 55.8 ppm for mordenite to 44 ppm for harkerite

X-ray diffraction studies of silica:titania sol-gel glasses

X-ray diffraction has been used to study a series of powdered silica:titania sol-gel glasses with titania contents ranging from a 'pure' silica sample through to high titania levels where phase separation may have occurred. Analysis of the data reveals the change in second and third neighbour coordination numbers with increasing Ti content and confirms that for low titanium contents the sol-gels are atomically mixed

Complete resolution of Si-O-Si and Si-O-Al fragments in an aluminosilicate glass by O-17 multiple quantum magic angle spinning NMR spectroscopy

Complete NMR resolution of Si-O-Si and Si-O-Al species in an aluminosilicate glass (NaAlSi3O8) is shown using O-17 multiple quantum magic angle spinning (MAS) NMR and indicates that no Al-O-Al is present at the detection limit of 0.5%

Sodium environments in dry and hydrous albite glasses: Improved Na-23 solid state NMR data and their implications for water dissolution mechanisms

The sodium environments in albite glasses with water concentrations ranging from 0 to 60 mol% were studied using Na-23 off-resonance quadrupole nutation and magic angle spinning (MAS) NMR spectroscopy. Crystalline albite was used as a model compound to demonstrate that off-resonance nutation is a suitable method for determination of the quadrupole coupling constant (C-q) for Na-23. Off-resonance nutation experiments gave a mean C-q = 1.75 +/- 0.2 MHz for all the albite glasses studied here. MAS NMR experiments were performed at three magnetic fields, 7.05 T, 9.4 T, and 14.1 T in order to deduce the mean isotropic chemical shift, delta(iso), and to provide an independent measurement of the values of C-q. The mean isotropic chemical shift is a strong function of dissolved water concentration, but the mean C-q is essentially constant at 2.1-2.2 +/- 0.2 MHz over the water concentration range studied. The distributions of both chemical shift and quadrupolar interactions decreases markedly with increasing water concentration, consistent with earlier suggestions that the hydrous glasses have a much more ordered structure. These new data using off-resonance nutation and faster MAS combined with higher applied magnetic fields supersede the Na-23 NMR data of Kohn et al. (1989a) and should be used in preference in devising or testing models for water dissolution mechanisms in albite melts and glasses. Our revised data provide no evidence for a change in water dissolution mechanism at 30 mol% H2O, but the other conclusions of Kohn et al. (1989a) and the principal features of the dissolution mechanism developed by Kohn et al. (1989a, 1992, 1994) are essentially unchanged

Impact of nitrogen seeding on confinement and power load control of a high-triangularity JET ELMy H-mode plasma with a metal wall

This paper reports the impact on confinement and power load of the high-shape 2.5MA ELMy H-mode scenario at JET of a change from an all carbon plasma facing components to an all metal wall. In preparation to this change, systematic studies of power load reduction and impact on confinement as a result of fuelling in combination with nitrogen seeding were carried out in JET-C and are compared to their counterpart in JET with a metallic wall. An unexpected and significant change is reported on the decrease of the pedestal confinement but is partially recovered with the injection of nitrogen.Comment: 30 pages, 16 figure