Determination of the plasma density in a current sheet from the profiles of the HeII 6560-Å and Hα spectral lines

The electron density in the midplane of a current sheet and far from it is determined from an analysis of the profiles of the HeII 6560-Å and H_α spectral lines. A new approach to calculating the Stark broadening of the HeII 6560-Å line is developed. The results obtained can be used to determine the plasma density in other experimental devices.     

Spectroscopic measurements of the parameters of the helium plasma jets generated in the plasma focus discharge at the PF-3 facility

The spectroscopic technique used to measure the parameters of the plasma jets generated in the plasma focus discharge and those of the plasma of the immobile gas through which these jets propagate is described. The time evolution of the intensities and shapes of spectral lines in experiments carried out with helium at the PF-3 facility was studied by means of electron-optical streak cameras. The plasma electron temperature, T ≈ 4–5 eV, was determined from the intensity ratio of two spectral lines, one of which (λ₁ = 5876 Å) belongs to neutral helium, while the other (λ₂ = 4686 Å), to hydrogen-like helium ions. The plasma density at different time instants was determined from the Stark broadening of these lines in the electric fields of different nature. The plasma density is found to vary from 4 × 10¹⁴ to 2 × 10¹⁷ cm^?3.     

Analytic approximations for the broadening of the spectral lines of hydrogen-like ions

Broadband approximate expressions for calculating the broadening of the spectral lines of hydrogen-like ions in a multicomponent plasma are derived taking into account both the influence of the interaction between plasma particles on the distribution function of the plasma microfield and the effect of the microfield dynamics on the broadening of the central component of the spectral line. With the approximate expressions proposed, the calculation of the shape of a given spectral line of a certain ion in a plasma with a given ion composition requires only a few seconds of computer time. The approximate expressions provide a good computational accuracy not only for the central component of the spectral line but also for the spectral line wings.     

Hydrogen lines in the infrared region and spectral background for the thomson scattering diagnostics of the iter divertor plasma

Calculations are made of the plasma spectral background, which is important for the Thomson scattering diagnostics in the ITER divertor. Theoretical grounds have been elaborated for computing the hydrogen spectral line shapes in the infrared spectral region for a divertor plasma in ITER. The shape of the P-7 Paschen line (transition n = 7 → n = 3) located near the laser scattering signal has been calculated for various lines of sight in the ITER divertor. Contributions from different mechanisms of broadening the P-7 line have been examined. The spectral intensities of bremsstrahlung and photorecombination continuum have been calculated. All calculations use data on the spatial distribution of temperatures and densities of all species of plasma particles computed with the SOLPS4.3 code for basic operation regimes of the ITER divertor.     

Pigment spectra and intermolecular interaction potentials in glasses and proteins

A model is proposed for chromophore optical spectra in solids over a wide range of temperatures and pressures. Inhomogeneous band shapes and their pressure dependence, as well as baric shift coefficients of spectral lines, selected by the frequency, were derived using Lennard-Jones potentials of the ground and excited states. Quadratic electron-phonon coupling constants, describing the thermal shift and broadening of zero-phonon lines, were also calculated. Experimentally, thermal shift and broadening of spectral holes were studied between 5 and 40 K for a synthetic pigment, chlorin, embedded in polymer hosts. The baric effects on holes were determined by applying hydrostatic He gas pressure up to 200 bar, at 6 K. Absorption spectra of pheophytin a, chlorophyll a, and beta-carotene in polymers and plant photosystem II CP47 complex were measured between 5 (or 77) and 300 K, and subject to Voigtian deconvolution. A narrowing of inhomogeneous bandwidth with increasing temperature, predicted on the basis of hole behavior, was observed as the shrinking of Gaussian spectral component. The Lorentzian broadening was ascribed to optical dephasing up to 300 K in transitions with weak to moderate linear electron-phonon coupling strength. The thermal broadening is purely Gaussian in multiphonon transitions (S(2) band of beta-carotene, Soret bands of tetrapyrrolic pigments), and the Lorentz process appears to be suppressed, indicating a lack of exponential dephasing. Density, polarity, polarizability, compressibility, and other local parameters of the pigment binding sites in biologically relevant systems can be deduced from spectroscopic data, provided that sufficient background information is available.     

Benchmarking of alternate theories for Stark broadening against experimental data from DIII-D diagnostics

Spectroscopy of high-n Balmer line transitions provides a means of measuring n _e and T _e in recombining plasmas [J. L. Terry et al., Phys. Plasmas 5, 1579 (1998)]. The relative intensities of Rydberg series lines near the ionization limit are a sensitive diagnostic of T _e , for T _e < 1.5 eV. Stark broadening of these same lines provides a measure of local n _e and, with less accuracy, of T _e . The accuracy of different theoretical models for Stark broadening [H.R. Griem, Spectral Line Broadening by Plasmas (Academic, New York, 1974); E. Oks, Stark Broadening of Hydrogen and Hydrogenlike Spectral Lines in Plasmas: The Physical Insight (Alpha Science International, Oxford, UK, 2006)] is evaluated by comparing values of n _e and T _e measured on DIII-D by divertor Thomson scattering (DTS) with those deduced from spectral profile analysis of Balmer series deuterium lines. In particular, the detailed dependence of line width on principal quantum number provides a sensitive metric for distinguishing which model best accords with experiment. Published in Russian in Fizika Plazmy, 2009, Vol. 35, No. 2, pp. 134–140. This text was submitted by the authors in English.     

C-terminal interactions of apolipoprotein E4 respond to the postprandial state

Increased triglyceride-rich lipoproteins (TGRLs) in the postprandial state are associated with atherosclerosis. We investigated whether the postprandial state induced structural changes at the apolipoprotein E4 (apoE4) C terminus, its principal lipid binding domain, using electron paramagnetic resonance (EPR) spectroscopy of a site-directed spin label attached to the cysteine of apoE4-W264C. Spin coupling between labels located in the C termini was followed after mixing with preprandial and postprandial human plasma samples. Our results indicate that postprandial plasma triggers a reorganization of the protein such that the dipolar broadening is diminished, indicating a reduction in C-terminal interaction. The loss of spectral broadening was directly correlated with an increase in postprandial plasma triglycerides and was reduced with delipidated plasma. The spin-labeled apoE4 displayed a lipid preference of VLDL > LDL > HDL in the preprandial and postprandial states. The apoE4 shift to VLDL during the postprandial state was accompanied by a loss in spectral broadening of the protein. These findings suggest that apoE4 associated with LDL maintains self-association via its C terminus and that this association is diminished in VLDL-associated protein. Lipolyzed TGRL reflected a depletion of the C-terminal interaction of apoE4. Addition of palmitate to VLDL gave a similar response as lipolyzed TGRL, suggesting that lipolysis products play a major role in reorganizing apoE4 during the postprandial state.     

Study of plasma fluctuations in the Tuman-3m tokamak using microwave reflectometry with an obliquely incident probing beam

Plasma fluctuations in the Tuman-3M tokamak are studied experimentally by analyzing backscattered radiation for different angles of incidence of the probing beam from the normal to the cut-off surface. The poloidal rotation velocity of the plasma fluctuations is determined from the Doppler shift of the reflected radiation spectrum measured on the edge of the tokamak during the transition to the H-mode. It is shown that, before the transition to the H-mode, the rotation velocity can be estimated quantitatively from the spectral shift or from the rate at which the phase of the reflected signal grows. The experimental data obtained during the transition to the H-mode provide evidence for the onset of a sheared poloidal flow. The shear makes it difficult to correctly estimate the poloidal rotation velocity in the improved confinement regime. The main mechanisms responsible for the broadening of the backscattered radiation spectra are considered. The turbulent diffusion coefficients determined under the assumption that the spectral broadening is diffusive in character are found to be close to those determined from the charged-particle balance.     

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.     

Reconstruction of the q and p profiles in ITER from external and internal measurements

A method is developed for calculating uncertainties in reconstructing the equilibrium profiles of the safety factor q and plasma pressure p in the ITER device from external magnetic measurements and from motional Stark effect line polarization (MSE-LP) and motional Stark effect line shift (MSE-LS) signals from excited NBI atoms inside the plasma core. It is shown that, with MSE-LP signals, as well as with MSE-LS signals (the use of which was recently proposed by Nova Photonics, Inc.), it is possible to substantially improve the reconstruction of the profiles that determine the plasma magnetic configuration.     

Cell Growth and Division: V. Error Analysis of the Collins-Richmond Equation

Error propagation in the Collins-Richmond equation is analyzed in order to obtain the ratio of the fractional error in rate of cell volume increase to the fractional error in each experimental variable. Typical data are analyzed numerically for the total errors resulting from counting statistics, from spectral broadening, and from volume calibration shift. The measurement of 10⁴ cells can give a precision of better than 10% in the volume growth rate with a volume resolution of 3%.     

Interaction of alpha-tocopherol with free fatty acids. Spatial organization of the complex

Stereoconfiguration of alpha-tocopherol-linoleic acid complex was studied using high resolution IH-NMR-spectroscopy. The addition of a fatty acid (linoleate) to alpha-tocopherol solution in CDCl3 resulted in the broadening of IH-NMR lines for OH- and phe-CH3-alpha-tocopherol groups. No changes in chemical shift values of IH-NMR lines for linoleic acid were observed after the addition of alpha-tocopherol to linoleic acid solution in CDCl3. It is concluded that in the complexes formed linoleic acid is located in the phenolic ring plane of alpha-tocopherol. The conclusion is supported by the data obtained on molecular models.     

Molecular Probes: What Is the Range of Their Interaction with the Environment?

We performed pressure-tuning hole-burning experiments on a modified cytochrome c protein in a glycerol/buffer glass. The shift and the broadening of the holes were investigated for various frequencies within the inhomogeneous band. On the basis of a simple model, we were able to estimate the interaction range between chromophore and protein. It is ~4.5 Å. The parameters that enter the model are the compressibility, the static mean-square displacement, the inhomogeneous width, and the average spectral shift per pressure. From this result and from our experiments on pressure-induced denaturing, we conclude that water molecules have to be brought very close to the chromophore during the denaturation process.     

NMR studies on solution structure of single-stranded oligonucleotides causing line broadening.

Unusual line broadening of 1H-NMR lines attributable to the proton (8H) of guanine residues was observed for all tetradeoxyoligonucleotides tested here which have a specific base sequence of dGXXG (X = A or T). For the same samples, line broadening was also obtained in the 31P-NMR spectra. These broadened signals did not become sharp up to 60 degrees C. This unusual spectral phenomenon has been attributed by 2D-NMR and differential NOE to the compact solution structure of the oligonucleotides.     

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.     

Theory of the Stark Effect in protein systems containing an electron donor–acceptor couple

Mixed-valency can occur in a variety of biological systems, such as the Cu(I)–Cu(II) pair in hemocyanin, Fe(II)–Fe(III) in many iron–oxo and iron–sulfur proteins, and Mn(II)–Mn(III) or Mn(III)–Mn(IV) in the photosynthetic water oxidase. The characterization of the ground states of such systems often has been controversial. Stark Effect spectroscopy is proving to be a valuable tool for the elucidation of systems of this type. The purpose of the present work is to develop theory for the spectral lineshape for the case where the electron donor and acceptor are coupled directly in a strong electric field. A mixed-valence dimer with an applied electric field aligned along the internuclear axis is studied using a two-site small-polaron model. Potential energy surfaces are calculated in the adiabatic (Born–Oppenheimer) approximation. It is shown that two nuclear coordinates (one totally symmetric and one antisymmetric) are coupled to the electronic motion, whereas only the antisymmetric coordinate is coupled in the absence of an electric field. For a strongly localized system, such as a protein system where electron donor and acceptor sites are separated by large distances, the potential surfaces become highly asymmetrical, but coupling to the totally symmetric mode is not significant. For a localized case corresponding to a valence-trapped two-metal cluster, the displacement along the totally symmetric coordinate is directly proportional to the applied field strength. Along the antisymmetric coordinate, the lowest potential surface is an asymmetric double well. For a delocalized (valence-averaged) two-metal cluster, there is significant displacement along the antisymmetric coordinate, an effect which also vanishes in the absence of an applied field. Contributions to the linewidth are estimated. Localized systems show larger field-induced shift in frequency maximum, whereas delocalized systems show greater field-induced line broadening.     

Modeling of electron heating and the spatiotemporal evolution of emission in a current-sheet plasma

Results are presented from a detailed study of the behavior of the electron temperature during the evolution of a current sheet by comparing the data from spectral measurements with the spatiotemporal evolution of the emission intensities of the atomic and ionic lines of the working gas (He) and impurities (C, O) calculated in the collisional-radiative model. It is shown that the electron temperature in the center of the sheet attains a value of T _e =110±40 eV; under these conditions, taking into account metastable states affects the calculated results only slightly. The spatial profiles of the electron temperature and the plasma emission in the spectral lines of various atoms and ions across the plasma sheet are calculated as functions of time. It is shown that as the electron temperature grows most of the spectral lines of atoms and ions of the working gas and impurities are depleted in the center of the sheet and the emission region shifts toward the periphery of the sheet. The results obtained confirm the previous conclusion that, in this regime, a hot plasma is formed in the center of the sheet.     

Evaluation of the ion temperature profile from measurements of the DD fusion products in the T-10 tokamak

Results are presented from measurements of the energy spectra and fluxes of the escaping charged fusion products and fluxes of fusion neutrons in ohmic regimes of the T-10 tokamak. The central temperature of the plasma ions is determined from the broadening of the energy spectra of thermonuclear protons and tritons. The ion temperature profile is evaluated from the dependence of the fluxes of charged fusion products on the radial plasma shift. It is proposed to use a single spectrometric detector with several collimators and slowing-down foils to measure the distribution of charged fusion products over pitch angles, which permits the determination of the ion temperature profile in a single shot. The feasibility of the method proposed is proved experimentally.     

Stark effect in P700, the primary electron donor of Photosystem I

Quadratic Stark effect in CP1 pigment-protein complex was examined at low temperatures in the red spectral region. The Stark spectra of samples containing P700 in reduced form exhibit a strong negative band at 704 nm, which disappears on chemical oxidation of P700. The change in permanent dipole moment, delta mu, of P700 on electronic excitation estimated from these spectra was found to be between 4.7 and 7.7 Debye units. It is suggested to reflect the charge-transfer contribution to the excited state of P700. For antenna chlorophyll, delta mu approximately equal to 1 D was obtained in accordance with the data for monomeric chlorophyll.