Electron temperature (T e) measurements by Thomson scattering system

Thomson scattering technique based on high power laser has already proved its superoirity in measuring the electron temperature (T _e and density (n _e) in fusion plasma devices like tokamaks. The method is a direct and unambiguous one, widely used for the localised and simultaneous measurements of the above parameters. In Thomson scattering experiment, the light scattered by the plasma electrons is used for the measurements. The plasma electron temperature is measured from the Doppler shifted scattered spectrum and density from the total scattered intensity. A single point Thomson scattering system involving a Q-switched ruby laser and PMTs as the detector is deployed in ADITYA tokamak to give the plasma electron parameters. The system is capable of providing the parameters T _e from 30 eV to 1 keV and n _e from 5 × 10¹²cm⁻³−5 × 10¹³cm⁻³. The system is also able to give the parameter profile from the plasma center (Z=0 cm) to a vertical position of Z=+22 cm to Z=−14 cm, with a spatial resolution of 1 cm on shot to shot basis. This paper discusses the initial measurements of the plasma temperature from ADITYA.     

Ultrasonic properties of water/sorbitol solutions

Ultrasonic longitudinal velocity and attenuation were measured for aqueous solutions of sorbitol at approximately 5 MHz. For pure sorbitol, the ultrasonic velocity reached 3200 m s⁻¹, consequently leading to a high acoustical impedance (around 5 × 10⁶ Rayleigh) and good matching between the ultrasonic transducers and material samples.     

Kinetic studies of chlorobenzene reactions with hydrogen atoms and phenyl radicals and the thermochemistry of 1-chlorocyclohexadienyl radicals

Atomic H and Cl were monitored by time-resolved resonance spectroscopy in the vacuum ultraviolet, following 193 nm laser flash photolysis of C₆H₅Cl and mixtures with NH₃, over 300-1020 K and with Ar bath gas pressures from 30 to 440 mbar. Below 550 K simple exponential decays of [H] were observed, and attributed to addition to form chlorocyclohexadienyl radicals. This addition was reversible over 550-630 K and the equilibrium constant was determined by a third law approach. The addition rate constant can be summarized as (1.51 ± 0.11) × 10⁻¹¹exp((−1397 ± 29)/T) cm³ molecule⁻¹ s⁻¹ (300-630 K, 1σ uncertainties), and the C-H bond dissociation enthalpy in 1-chlorocyclohexadienyl was determined to be 108.1 ± 3.3 kJ mol⁻¹ at 298 K. At higher temperatures the photolysis of chlorobenzene yielded H atoms, which is attributed to the reaction of phenyl with chlorobenzene with a rate constant of (4.5 ± 1.8) × 10⁻¹⁰exp((−4694 ± 355)/T) cm³  molecule⁻¹ s⁻¹ over 810-1020 K. These and other reaction pathways are discussed in terms of information about the potential energy surface obtained via B3LYP/6-311G(2d,d,p) density functional theory.     

Synthesis and characterization of silicon carbonitride films by plasma enhanced chemical vapor deposition (PECVD) using bis(dimethylamino)dimethylsilane (BDMADMS), as membrane for a small molecule gas separation

Silicon carbonitride thin films have been deposited by plasma enhanced chemical vapor deposition (PECVD) from bis(dimethylamino)dimethylsilane (BDMADMS) as a function of X = (BDMADMS/(BDMADMS + NH₃)) between 0.1 and 1, and plasma power P (W) between 100 and 400 W. The microstructure of obtained materials has been studied by SEM, FTIR, EDS, ellipsometrie, and contact angle of water measurements. The structure of the materials is strongly depended on plasma parameters; we can pass from a material rich in carbon to a material rich in nitrogen. Single gas permeation tests have been carried out and we have obtained a helium permeance of about 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ and ideal selectivity of helium over nitrogen of about 20.     

High frequency shear ultrasonic properties of water/sorbitol solutions

Dynamic viscoelastic properties (G′ and G′′), ultrasonic shear velocity and attenuation were measured for aqueous solutions of sorbitol at 5 MHz. For pure sorbitol, the shear ultrasonic velocity reached 1470 m s⁻¹ with a density of 1500 kg m⁻³, consequently leading to a high acoustical impedance compared with “classical” polymers (polystyrene, nylon, polyethylene, Teflon, etc.). We demonstrate that this surprisingly high shear ultrasonic velocity for a viscoelastic material was due to the fact that the glass transition begins at a concentration above 85% of sorbitol in water. Hence, pure sorbitol is an ideal coupling material for high frequency shear experiments.     

Rayleigh scattering in fused silica samples for gravitational wave detectors

Laser interferometer gravitational wave detectors require very high optical quality test masses. We report the bulk Rayleigh scattering in high quality fused silica samples. Results show that the scattering of the high quality fused silica is similar for various grades of fused silica from Heraeus. The total integrated scattering is about 0.7 ppm cm^− 1at 1064 nm wavelength, which agrees with the theoretical value calculated using known fused silica parameters. All samples show Rayleigh scattering ratio inhomogeneity of ~ 4%.     

Microwave diagnostics of ultracold neutral plasma

The microwave method is suggested to diagnose the ultracold neutral plasma. Based on the calculations of the dipole radiation, we derive the microwave scattering cross section of the ultracold neutral plasma, and microwave power scattered by the ultracold plasma is calculated as a function of time. The scattering cross section is nearly ¹⁰−11 m².     

Lineshape analysis of the J = 3 ← 2 and J = 5 ← 4 rotational transitions of room temperature CO broadened by N2, O2, CO2 and noble gases

Collisional relaxation has been considered for millimeter lines of carbon monoxide at room temperature. Accurate measurements of carbon dioxide- and rare gases-broadened widths have been performed on the J = 3 ← 2 rotational line of ¹²CO by using a video-type spectrometer. Measurements of nitrogen-, oxygen-, and xenon-broadened widths of the J = 5 ← 4 rotational line of ¹³CO were also carried by using a frequency-modulated spectrometer. A lineshape study performed on all the investigated binary systems provide confirmation that Voigt profile is not a suitable model to analyse experimental lines in the millimeter-waves region. On one hand, using this profile in the low pressure range, i.e. in the Doppler regime, the retrieved collisional linewidths do not follow a linear variation with the perturbing gas pressure. On the other hand, regardless of the pressure, lineshapes exhibit a narrowed profile. An accurate analysis of the pressure dependence of relaxation rates show that the Galatry profile is not appropriate and that experimental lineshapes are actually Speed Dependent Voigt profiles. Accurate broadening parameters were retrieved from this profile and compared to previous reported values and predictions calculated from the Robert-Bonamy formalism. Finally a variation of the ratio of relaxation speed dependence to broadening parameters versus relative masses of the collision partners is presented.     

N2-, H2-, and He-induced collisional broadening of the J = 24 ← 23 transition of HC3N located near 218.3 GHz at different temperatures

We report on experimental collisional relaxation of the J = 24 ← 23 line of HC₃¹⁴N, located near 218.3 GHz, induced by nitrogen, hydrogen, and helium. The measurements were carried out at selected temperatures in the 235-350 K range using a video-type spectrometer. The foreign gas broadening parameters and their temperature dependences were determined assuming Voigt lineshape profiles and the usual T⁻ⁿ temperature law. The experimental broadening parameters are compared with results derived using the ATC collisional formalism.     

Burning velocity of triple flames with gentle concentration gradient

We investigated the local flame speed of a two-dimensional, methane-air triple flame in a rectangular burner. The velocity fields and the concentration profiles were measured with particle image velocimetry and the Rayleigh scattering method, respectively. There was a requisite combination of initial velocity and initial concentration gradient for consistency of the local concentration gradient at the leading edge of the flame. In these cases, the flame curvatures were also consistent. Accordingly, the burning velocity, defined as local flow velocity at the triple point, was determined by the flame curvature. The burning velocity increased with increasing flame curvature, when the curvature was near zero. After that, the burning velocity decreased with increasing curvature. The peak value thus exceeded the adiabatic one-dimensional laminar burning velocity. Comparing the effects of the measured flame stretch rate on the flow strain κ_s and flame curvature κ_c, κ_s is larger and increases more rapidly than κ_c for flame curvatures satisfying 1/R_f < 250 m⁻¹ and then becomes constant while κ_c still increases for 250 m⁻¹ < 1/R_f, so that κ_c becomes much larger than κ_s. There is also a peak in burning velocity at roughly the transition in flame curvature specified above. Therefore, the burning velocity for a low concentration gradient correlates with the flame stretch rate.     

The spectral sensitivity of long period gratings fabricated in elliptical core D-shaped optical fibre

Long period gratings (LPGs) were written into a D-shaped optical fibre that has an elliptical core with a W-shaped refractive index profile and the first detailed investigation of such LPGs is presented. The LPGs’ attenuation bands were found to be sensitive to the polarisation of the interrogating light with a spectral separation of about 15 nm between the two orthogonal polarisation states. A finite element method was successfully used to model many of the behavioural features of the LPGs. In addition, two spectrally overlapping attenuation bands corresponding to orthogonal polarisation states were observed; modelling successfully reproduced this spectral feature. The spectral sensitivity of both orthogonal states was experimentally measured with respect to temperature and bending. These LPG devices produced blue and red wavelength shifts depending upon the orientation of the bend with measured maximum sensitivities of −3.56 and +6.51 nm m, suggesting that this type of fibre LPG may be useful as a shape/bend orientation sensor with reduced errors associated with polarisation dependence. The use of neighbouring bands to discriminate between temperature and bending was also demonstrated, leading to an overall curvature error of ±0.14 m⁻¹ and an overall temperature error of ±0.3 °C with a maximum polarisation dependence error of ±8 × 10⁻² m⁻¹ for curvature and ±5 × 10⁻² °C for temperature.     

Velocity changing collisions in the laser saturation spectra of Rb D2 F″ = 2

The saturation absorption technique is applied to the ⁸⁷Rb ²S_1/2 F″ = 2 → ²P_3/2 F′ = 1, 2 and 3 transitions to study the effect of velocity changing collisions (VCC). The VCC caused Doppler pedestal increases with argon pressure from 0 to 110 mTorr and decreases with modulation frequencies of 700-3200 Hz. The resonances of the velocity selective, saturated optical pumping are washed out for pressure of 110 mTorr. The magnitude of the Doppler pedestal relative to the homogeneous features, yields a rate for velocity changing collisions of 6.5 ± 0.2 × 10⁻¹⁰ cm³ s⁻¹.     

Sliding tribological properties of untreated and PIII-treated PETP

Poly(ethylene terephthalate) (PETP) was treated by plasma immersion ion implantation (PIII or PI³) in nitrogen. The surface changes were characterised by XPS and water contact-angle measurements. Sliding tribological properties of untreated and nitrogen PIII-treated PETP against conventional low carbon structural steel S235 were studied under dry and water-lubricated conditions by a pin-on-disc tribometer.XPS results suggested the evolution of surface composition and bonding towards those of amorphous hydrogenated carbon-nitride. Water contact-angle decreased implying increased surface wettability. At a very low Pv factor (0.0075 MPa m s⁻¹) for the nitrogen PIII-treated PETP the dry friction coefficient was smaller than, while the lubricated friction coefficient was similar to, the corresponding value of the untreated variant. At higher Pv factors (near 0.1 MPa m s⁻¹), however, both the dry and lubricated friction coefficients were higher for the treated sample than for the untreated variant, suggesting an increased adhesion component of friction for the nitrogen PIII-treated PETP in this region.     

Observation of laser light scattering by a turbulent gas without seeding

An experiment of laser light scattering by a turbulent highly subsonic free jet of air is presented. The originality of the method lies in the fact that no particle seeding is needed. The experimental scattering cross section, which can be interpreted from the three-dimensional spectral density of temperature fluctuations, is compared to the theoretical one obtained by turbulent mixing theories. The scattered field time correlations measured in the heterodyne mode are interpreted by considering the Doppler effect on moving turbulent eddies and compared with theory. The intensity time correlations measured in the homodyne mode are interpreted in terms of local properties of the turbulence.     

Measurement of thomson and rayleigh scattering in a preionizationZ-pinch

A 90° scattering experiment with a preionizationZ-pinch is described. The first part describes conventional measurements of the electron temperature and density (Thomson scattering). In the second part of the experiment Rayleigh scattering from excited hydrogen atoms was observed during very early phases of the discharge. This observation is possible because the Rayleigh scattering cross section of hydrogen atoms in the second and third quantum states is very large because of the small difference in the energy of the photons ofH _α (6563 Å) and the light of a ruby laser (6943 Å). Spectral resolution of this part of the scattered light yields a minimum value for the ion temperature.     

Macroscopic polarization and thermal conductivity of GaN

We theoretically investigated the effect of macroscopic polarization (sum of spontaneous and piezoelectric polarization) on the thermal conductivity of wurtzite GaN. Macroscopic polarization contributes to the effective elastic constant of the GaN and thus modifies the phonon group velocity. We used the revised phonon velocity to estimate the Debye frequency and temperature. Different phonon scattering rates were calculated as functions of the phonon frequency. The thermal conductivity of GaN was estimated using revised parameters such as the phonon velocity and phonon relaxation rate. The revised thermal conductivity at room temperature increased from 250 to 279 W m⁻¹ K⁻¹ due to macroscopic polarization. The method we developed can be used for thermal budget calculations for GaN optoelectronic devices.     

Determination of interfacial energies in the aminomethylpropanediol-neopentylglycol organic alloy

The grain boundary groove shapes for solid aminomethylpropanediol in equilibrium with eutectic aminomethylpropanediol-neopentylglycol liquid were directly observed by using a horizontal temperature gradient stage. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient, solid-liquid interfacial energy and grain boundary energy of solid aminomethylpropanediol in equilibrium with eutectic aminomethylpropanediol-neopentylglycol liquid have been determined to be (5.3 ± 0.5) × 10⁻⁸ K m, (8.5 ± 1.3) × 10⁻³ J m⁻² and (16.8 ± 2.9) × 10⁻³ J m⁻², respectively.     

Thermal desorption of dysprosium from tungsten microcrystal

Activation energy for thermal desorption of dysprosium from a tungsten microcrystal of about 300 nm diameter was determined by means of the field-emission method. The desorption was detected from the whole W emitter surface in the temperature range 1490-1665 K for dysprosium average coverage θ < 0.06 monolayer. The average activation energy was determined to be 4.09 ± 0.06 eV/atom and the frequency factor to be about 10¹¹ s⁻¹. The energy may mainly concern the desorption from the atomically rough regions of the microcrystal.     

Scattering of F atoms and anions on a TiO2(1 1 0) surface

Results of a study of energy losses and electron transfer processes for grazing scattering of fluorine atoms and anions scattering along different azimuthal orientations of the TiO₂ crystal are presented. We observe strong variations in the overall intensity of scattered particles which are due to channelling effects. The energy losses do not show strong variations as a function of crystal azimuth except for the case of scattering along the (0 0 1) direction between the bridging oxygen atom rows, where we also observe differences in the energy losses of scattered ions and neutrals. We attribute this to the fact that larger F⁻ survival occurs for trajectories staying farther from the surface, when also the energy losses remain small. The overall characteristics of energy losses are attributed mainly to trajectory effects due to scattering in regions of different electron density. Measurements of the ratio of scattered ions to the total scattered flux, i.e. the ion fractions which reflect electron capture and loss processes, show that these are not the same for incident anions and atoms. A strong difference for scattering along the (0 0 1) direction is observed, where at low incident energies a strong survival of incident ions occurs. These results are tentatively discussed in terms of non resonant electron capture at lattice O⁻ sites and electron loss into the conduction band or by collisional detachment with bridging O atoms.     

A thermometry technique based on atomic lineshapes using diode laser LIF in flames

We report on the development of a novel diode laser thermometry technique permitting temperature measurements in flames based on the fluorescence lineshapes of an atomic tracer species. The technique, which we term OLAF (one-line atomic fluorescence) requires only a single diode laser source for excitation, is simple to implement, and has excellent spatial resolution. Temperatures are deduced from the 5²P_1/2 → 6²S_1/2 transition of atomic indium, the lineshape of which is highly sensitive to temperature changes at typical flame conditions. A rigorous validation is performed in a reference flame with comparisons to measurements by CARS and by Na-line reversal, and to numerical simulations.