Creation and investigation of powerful EUV sources (λ ≈ 13.5 nm)

Results are presented from experimental studies of repetitively pulsed EUV (λ = 13.5 ± 0.135 nm) sources based on a laser-initiated discharge in tin vapor between rotating disk electrodes. Radiative characteristics of two sources with different systems of tin supply onto the electrode surface and different types of power supply have been compared. A number of new effects have been revealed at pulse repetition rates as high as ∼4000 Hz. A mean radiation power of 520 W into the 2π solid angle has been achieved in the spectral band 13.5 ± 0.135 nm at a deposited electrical power of 24 kW.     

Fast measurements of the limiter surface temperature and the heat flux onto the limiter in the T-11M tokamak by using an IR radiometer

The limiter surface temperature is measured with a high-speed IR radiometer (λ⋍3–6 μm) during a T-11M tokamak discharge. The IR radiometer was absolutely calibrated under steady-state operating conditions: the limiter was heated by a special inner heater, and the limiter temperature was measured with a thermocouple. Based on these measurements, the heat fluxes from the plasma onto the limiter surface during the discharge are determined. The measurement technique is discussed, and the data on the limiter surface temperature and the heat flux to the limiter for different regimes of the T-11M operation are presented. __________ Translated from Fizika Plazmy, Vol. 28, No. 10, 2002, pp. 872–876. Original Russian Text Copyright ? 2002 by Lazarev, Alekseev, Belov, Mirnov.     

First results from plasma density measurements in the FTU tokamak by means of a two-frequency pulsed time-of-flight refractometer

A pulsed time-of-flight refractometer was developed and tested to determine the mean plasma density in the T-11M tokamak by measuring the propagation time of nanosecond microwave pulses in plasma. Later, it was also proposed to use such an instrument to measure and control the mean plasma density in the ITER tokamak by probing the plasma with an extraordinary wave, the electric field of which is perpendicular to the magnetic field in plasma, in the transparency window at frequencies of 50–100 GHz. To avoid the effect of the density profile shape on the measurement results in the nonlinear mode of refractometer operation (near the cutoff), a system operating at two different probing frequencies was developed and tested. Such a system provides two values of the time delay, which can be used to estimate the peaking factor of the density distribution α and correctly determine the linear density 〈Nl〉, regardless of the density profile (assuming a smooth density profile of the form of N(ρ) = N(0)(1 − ρ²)^α, where N(0) is the central plasma density and ρ = r/a is the normalized plasma radius). The first experiments on density measurements in the FTU tokamak performed with this refractometer are described, and results from these experiments are presented. The formation of a thin dense plasma layer in the zone of a strong magnetic field (the so-called MARFE layer) at a relatively low (for FTU) plasma density of ∼6 × 10¹⁹ m⁻³ was detected. The thickness of this layer, determined from the refractometry data, agrees well with the data obtained using a digital camera.     

SOLPS4.3 Modeling of Lithium Transport and Noncoronal Radiation in the T-15 Tokamak with Lithium Emitter−Collector Scheme in Use

The lithium emitter?collector scheme has been successfully used on limiter tokamak T-11M for a long time and is therefore one of the most mature concepts of liquid lithium-assisted power and particle exhaust. In the present paper, a possible application of the emitter?collector scheme to the divertor tokamak T-15 is analyzed with the 2D transport code SOLPS4.3. Modeling indicates that placing the lithium limiter at the outer midplane of the vessel results in the widest possible spreading of lithium over the scrape-off layer, whereas lithium deposition in this case is localized primarily at the upper outer target plate. The power exhaust capability of the lithium emitter?collector scheme is also studied. It is often presumed on the basis of a simple 0D analysis that the noncoronality can bring the lithium radiation capability in line with the other low-Z impurities typically involved in the divertor power exhaust (such as carbon and nitrogen). However, detailed 2D modeling shows that in spite of the significant increase of the Li cooling rate due to the noncoronal effects, the contribution of lithium radiation to divertor power balance remains marginal, unless the lithium inventory in the edge becomes close to the deuterium one.     

Investigation of the Edge Plasma Parameters and Measurements of the Plasma Longitudinal Rotation Velocity by a Mach Probe in a Lithium Experiment on the T-11M Tokamak

The edge plasma parameters were measured by means of a Mach probe in a lithium experiment on the T-11M tokamak. The angular and radial distributions of the ion saturation current, along with the radial distribution of the electron temperature, were obtained in different modes of tokamak operation. The radial distributions of the electron temperature and ion saturation current in the main operating mode (L-mode) revealed a peak in the scrape-off-layer of the vertical limiter (lithium emitter), which can indicate the formation of a magnetic island in this region. The measured plasma flow velocity along the magnetic field was found to be close to one-half of the ion sound velocity for Li⁺ ions.     

Use of additional helium puffing for the diagnostics of plasma parameters at the FT-2 tokamak

The experiments carried out at the FT-2 tokamak in which additional pulsed puffing of helium into the hydrogen plasma was used for diagnostic purposes are considered. To estimate the necessary content of helium ions in the experiments on studying short-scale plasma oscillations, the ionization-recombination balance was simulated numerically under the assumption of a toroidally homogeneous influx of the working gas onto the boundary of the plasma column. In these simulations, the effective density of the neutral gas incident on the plasma boundary was determined by the iteration method, which made it possible to provide agreement between the obtained solution and the experimental discharge conditions. In particular, the correspondence of the determined admixture content to both the plasma quasineutrality condition and the value of the effective charge Z _eff, as well as agreement between the calculated and measured plasma density profiles, was ensured. The simulations were performed under the assumption of anomalous diffusion coefficients for all plasma components. The temporal variations of the ionization-recombination balance were checked by comparing them with the measured spectra of radiation in the HeI, HeII, and H_?? lines. In the current drive experiments, variations in n _e (r) at the discharge periphery were examined by the method based on the proportionality of the intensity ratio of the helium spectral lines, HeI(668 nm)/HeI(728 nm), to the plasma density. In these calculations, the factors relating the intensity ratio of these lines to the plasma density were taken from the literature on spectral diagnostics.     

The effect of low-intensity laser irradiation in the blue, green, and red spectral ranges on healing of experimental skin wounds in rats

The effects of low-intensity laser irradiation in the red (632.8 nm), green (532 nm), and blue (441.2 nm) spectral ranges on wound healing has been studied in rats. The effect of the traditionally used red laser irradiation has been compared with the effect caused by laser irradiation in other spectral ranges, aiming to support the provisional hypothesis that a similar healing effect could be achieved at lower doses of wound irradiation by lasers emitting in the blue and green spectral ranges. The following parameters have been used to characterize healing of the experimental wounds: the functional activity of phagocytes in the wound exudate, which was determined from luminol-dependent chemiluminescence, the phagocyte number; the wound exudates’ antioxidant activity; and the rate of healing, which was determined as the change of the wound surface area. It was found that in all cases the laser irradiation accelerated the healing of wounds. Exposure to red laser irradiation at the dose of 1.5 J/cm²), and to blue or green laser irradiation at a dose of 0.75 J/cm² shortened the time of the wound healing from 22 to 17 and 19 days, respectively. The functional activity of leukocytes in irradiated groups increased by day 5 after surgery, whereas in the control group it decreased. The superoxide dismutase activity increased in all experimental groups by day 5 after surgery. Laser irradiation in the red spectral range at a dose of 1.5 J/cm² resulted in a larger increase in superoxide dismutase activity, as compared to that found after exposure to laser irradiation in the blue and green spectral ranges at a dose of 0.75 J/cm².     

CXSFIT Code Application to Process Charge-Exchange Recombination Spectroscopy Data at the T-10 Tokamak

The applicability of the CXSFIT code to process experimental data from Charge-eXchange Recombination Spectroscopy (CXRS) diagnostics at the T-10 tokamak is studied with a view to its further use for processing experimental data at the ITER facility. The design and operating principle of the CXRS diagnostics are described. The main methods for processing the CXRS spectra of the 5291-Å line of C⁵⁺ ions at the T-10 tokamak (with and without subtraction of parasitic emission from the edge plasma) are analyzed. The method of averaging the CXRS spectra over several shots, which is used at the T-10 tokamak to increase the signal-to-noise ratio, is described. The approximation of the spectrum by a set of Gaussian components is used to identify the active CXRS line in the measured spectrum. Using the CXSFIT code, the ion temperature in ohmic discharges and discharges with auxiliary electron cyclotron resonance heating (ECRH) at the T-10 tokamak is calculated from the CXRS spectra of the 5291-Å line. The time behavior of the ion temperature profile in different ohmic heating modes is studied. The temperature profile dependence on the ECRH power is measured, and the dynamics of ECR removal of carbon nuclei from the T-10 plasma is described. Experimental data from the CXRS diagnostics at T-10 substantially contribute to the implementation of physical programs of studies on heat and particle transport in tokamak plasmas and investigation of geodesic acoustic mode properties.     

The effect of charge exchange with neutrals on the saturation of the spectral line intensities of multicharged ions in plasma

The influence of charge-exchange processes on the spectral line intensities of impurity ions in the edge and core plasmas of fusion devices is considered. It is found that, at a sufficiently high density of neutrals, the rate at which the atomic states are populated through charge exchange becomes independent of the neutral density, which results in the saturation of the spectral line intensities. This effect can substantially limit the efficiency of impurity-ion spectroscopy. Conditions under which the saturation effect manifests itself are examined for both the edge and core plasma regions in the presence of fast neutral beams. The results of calculations for the edge plasma are used to interpret the experimental data from the TORE SUPRA tokamak. It is shown that, in the central plasma region, the intensities of the visible spectral lines associated with the charge exchange of impurity ions in the course of neutral beam injection decrease (rather than increase, as was expected earlier) with increasing ion charge.     

Calix[4]arene based molecular sensors with pyrene as fluoregenic unit: Effect of solvent in ion selectivity and colorimetric detection of fluoride

Fluorescent molecular sensors having excimer emission property have been designed and synthesised incorporating calix[4]arene derivatives in cone and 1,3-alternate conformation as ionophore and two pyrene moieties at close proximity as fluorophore. They exhibit strong excimer emission around 515 nm, which is used to monitor interaction of metal ions with the ionophores. Ion-binding study of these fluoroionophore has been investigated in acetonitrile-chloroform and THF-H₂O with a wide range of cations and anions and the recognition process is monitored by luminescence, UV-Vis and ¹H NMR (for F⁻) spectral changes. The present study demonstrated profound influence of solvent in ion selectivity, in acetonitrile-chloroform they formed complexes with Hg²⁺, Pb²⁺, Cu²⁺ and Ni²⁺, whereas in THF-H₂O they exhibit selectivity only for Cu²⁺. In the case of anions, selectivity for only F⁻ with color change is observed. Composition of the complexes formed was determined from mass spectrometry and the binding constants were determined from fluorescence titration data. The reasons for formation of excimer emission, quenching of it in presence of certain metal ions, role of solvent in selectivity and energy/electron transfer process involved in the ion-recognition event have been discussed on the basis of experimental data.     

Metal-free and metal-substituted cytochromes c. Use in characterization of the cytochrome c binding site.

The luminescent properties of metal-free, tin(IV) and zinc(II) cytochromes c have been used to characterize the interaction of cytochrome c with mitochondria and cytochrome oxidase. Diminution in the fluorescence yields of tin and zinc cytochrome c occur when these derivates bind to cytochrome oxidase or mitochondria. Based upon spectral overlap and quantum yield, the distance between the porphyrin rings of cytochrome a and cytochrome c is estimated according to Forster theory to be in the neighborhood of 3.5 nm. Measurements of the polarized emission of metal-free 'porphyrin' cytochrome c when bound to oriented layers of cytochrome c oxidase indicate that the porphyrin is bound obliquely to the plane of the oxidase layers with an angle of about 70 degrees C from heme plane to membrane plane. It is proposed that these data have significance for elucidation of electron transfer mechanisms.     

Identification of the plasma boundary shape and position in the Damavand tokamak

A series of experiments and numerical calculations have been done on the Damavand tokamak for accurate determination of equilibrium parameters, such as the plasma boundary position and shape. For this work, the pickup coils of the Damavand tokamak were recalibrated and after that a plasma boundary shape identification code was developed for analyzing the experimental data, such as magnetic probes and coils currents data. The plasma boundary position, shape and other parameters are determined by the plasma shape identification code. A free-boundary equilibrium code was also generated for comparison with the plasma boundary shape identification results and determination of required fields to obtain elongated plasma in the Damavand tokamak.     

Diagnostics of MHD instability in the Globus-M spherical tokamak

The paper describes a diagnostic system for studying MHD plasma perturbations in the Globus-M spherical tokamak (a major radius of 0.36 m, a minor radius of 0.24 m, and an aspect ratio of 1.5). The system includes a poloidal and a toroidal array consisting of 28 and 16 Mirnov probes, respectively, as well as a 32-channel proportional soft X-ray detector. Methods are described for calculating the poloidal and toroidal numbers of the dominant helical perturbations by using data from probe measurements. Results are presented of processing the experimental data from some tokamak discharges with a plasma current of 150–250 kA, an average electron density of up to 10²⁰ m^?3, and a toroidal magnetic field of 0.4 T. Specific features of MHD perturbations and their influence on the parameters of the plasma column in different stages of a discharge are briefly discussed.     

Measurements of the plasma radiative loss profile in the M-11M tokamak with the help of a tangential-view AXUV photodiode array

The plasma radiative loss profile in the T-11M tokamak operating with a lithium limiter was measured using a sixteen-channel absolute extreme-ultraviolet photodiode array. The field of view of the detector was set in a vertical plane tangential to the plasma column axis. The radiative loss profile was recovered by solving an inverse problem under the assumption of toroidal and poloidal symmetry of the plasma column. A stable algorithm is developed for solving the problem with this geometry, and the possible errors of the method are evaluated. The radiative loss profiles and their evolution in various tokamak regimes are derived.     

Microwave measurements of the time evolution of electron density in the T-11M tokamak

Unambiguous diagnostics intended for measuring the time behavior of the electron density and monitoring the line-averaged plasma density in the T-11M tokamak are described. The time behavior of the plasma density in the T-11M tokamak is measured by a multichannel phase-jump-free microwave polarization interferometer based on the Cotton-Mouton effect. After increasing the number of simultaneously operating interferometer channels and enhancing the sensitivity of measurements, it became possible to measure the time evolution of the plasma density profile in the T-11M tokamak. The first results from such measurements in various operating regimes of the T-11M tokamak are presented. The measurement and data processing techniques are described, the measurement errors are analyzed, and the results obtained are discussed. We propose using a pulsed time-of-flight refractometer to monitor the average plasma density in the T-11M tokamak. The refractometer emits nanosecond microwave probing pulses with a carrier frequency that is higher than the plasma frequency and, thus, operates in the transmission mode. A version of the instrument has been developed with a carrier frequency of 140 GHz, which allows one to measure the average density in regimes with a nominal T-11M plasma density of (3–5)×10¹³ cm^?3. Results are presented from the first measurements of the average density in the T-11M tokamak with the help of a pulsed time-of-flight refractometer by probing the plasma in the equatorial plane in a regime with the reflection of the probing radiation from the inner wall of the vacuum chamber.     

Charge-exchange recombination spectroscopy of the plasma ion temperature at the T-10 tokamak

Charge-exchange recombination spectroscopy (CXRS) based on a diagnostic neutral beam has been developed at the T-10 tokamak. The diagnostics allows one to measure the ion temperature profile in the cross section of the plasma column. In T-10 experiments, the measurement technique was adjusted and the elements of the CXRS diagnostics for ITER were tested. The used spectroscopic equipment makes it possible to reliably determine the ion temperature from the Doppler broadening of impurity lines (helium, carbon), as well as of the spectral lines of the working gas. The profiles of the plasma ion temperature in deuterium and helium discharges were measured at different plasma currents and densities, including with the use of active Doppler measurements of lines of different elements. The validity and reliability of ion temperature measurements performed by means of the developed CXRS diagnostics are analyzed.     

Effect of electron-cyclotron resonance heating conditions on the local parameters of short-wavelength plasma turbulence in the L-2M stellarator

Changes in the energy spectra of short-wavelength (k _s ≈ 35 cm^?1) plasma density fluctuations in the local region of the plasma column (r/a = 0.5–0.6) of the L-2M stellarator were studied by the method of collective scattering of 150-GHz radiation. The plasma was heated at the second harmonic of the electron gyrofrequency, the microwave heating power being in the range of 90–170 kW. A sector limiter was introduced in the peripheral plasma (r/a ≥ 0.8), and the Shafranov shift of the magnetic axis was varied by varying the vertical magnetic field. The results of measurements were averaged over 9–16 discharges. It is found that an increase in the heating power and/or the introduction of the sector limiter in the plasma lead to an increase in the energy of density fluctuations, which correlates with a decrease in the plasma energy lifetime. In the spectra of fluctuations, a broad spectral band in the range of 3–50 kHz was observed in which the spectral density was one order of magnitude higher than in the rest of the spectrum. Analysis of the Fourier spectra showed that the introduction of the sector limiter in the plasma resulted in an increase in both the spectral density of fluctuations in the range of 3–50 kHz and the fraction of quasi-coherent structures in turbulent density fluctuations.     

Spectral analysis of Delayed Luminescence from human skin as a possible non-invasive diagnostic tool

In vivo measurements of Delayed Luminescence (DL), the low-level photo-induced emission which lasts for a longer time after switching off the excitation light, have been performed on human skin, with the aim to develop a technique for optical biopsy. Preliminary tests have been performed on healthy volunteers, measuring the time decays of the spectral components (λ_emiss = 400–800 nm) starting 10 μs after switching off the excitation (λ_exc = 337 nm). Significant differences in the decay trends of DL from different subjects were revealed and quite a good reproducibility for the same subject was observed. The modeling of experimental data has been examined in detail in order to get parameters, characterizing the theoretical fit, whose changes may be correlated with age differences and seasonal variations. Proceedings of the XVIII Congress of the Italian Society of Pure and Applied Biophysics (SIBPA), Palermo, Sicily, September 2006.     

Comparison of interactions between human serum albumin and silver nanoparticles of different sizes using spectroscopic methods

Three different sizes (15.9 ± 2.1 nm, 26.4 ± 3.2 nm and 39.8 ± 4.0 nm, respectively) of citrate‐coated silver nanoparticles (SNPs) have been synthesized and characterized. The interactions of the synthesized SNPs with human serum albumin (HSA) at physiological pH have been systematically studied by UV‐vis absorption spectroscopy, fluorescence spectroscopy, synchronous fluorescence spectroscopy, three‐dimensional fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The results indicate that the SNPs can bind to HSA with high affinity and quench the intrinsic fluorescence of HSA. The binding constants and quenching rate constants were calculated. The apparent association constants (K_app) values are 2.14 × 10⁴ M^–1 for 15.9 nm SNP, 1.65 × 10⁴ M^–1 for 26.4 nm SNP and 1.37 × 10⁴ M^–1 for 39.8 nm SNP, respectively. The values of binding constant obtained from the fluorescence quenching data match well with that determined from the absorption spectral changes. These results suggest that the smaller SNPs have stronger interactions to HSA than the larger ones at the same concentrations. Synchronous fluorescence, three‐dimensional fluorescence and CD spectroscopy studies show that the synthesized SNPs can induce slight conformational changes in HSA. Copyright © 2014 John Wiley & Sons, Ltd.     

Vibrational mode analysis of 2-aminoadenine and its deuterated species from Raman and ultraviolet resonance Raman data

Resonance Raman spectroscopy data of 2-aminoadenine and its deuterated species (C8-deuterated, N-deuterated and C8-, N-deuterated derivatives) in aqueous solution have been collected in the spectral region between 400 and 1800 cm^–1, by using ultraviolet excitation wavelengths (_exc = 222, 257 and 281 nm) located in the three main UV absorption bands corresponding to the strongly allowed electronic transitions of the molecule of interest. Moreover, a Raman spectrum has been recorded under off-resonance conditions with a visible excitation (_exc= 488 nm). In order to assign the 2-aminoadenine in-plane vibrational bands displayed in the RRS spectra, a normal coordinate analysis has been performed by means of an empirical internal valence force field. These calculations are based on our recent normal mode analysis of adenine and guanine nucleic bases and their deuterated species, which was based on the joint use of resonance Raman spectroscopy and neutron inelastic scattering data. In the 2-aminoadenine force field proposed here, the diagonal force constants have been directly transferred from those recently obtained for adenine (and from guanine as concerns the 2-amino group), the interaction force constants (off-diagonal) then being adjusted on the basis of the actual experimental data from 2-aminoadenine and its deuterated species. The current force field is also able to assign infrared and Raman data obtained by other authors from polycrystalline samples of the pure species. Correspondence to: M. Ghomi