Diagnostics of soft X-ray emission from the plasma of a fast capillary discharge

Results are presented from time-resolved measurements of the soft X-ray emission in the 10-to 40-eV spectral range from the plasma of a pulsed capillary discharge in argon at current pulse amplitudes of up to 26 kA and a current rise time of ～10¹² A/s. The experiments were carried out with 0.3-cm-diameter 15.7-cm-long ceramic capillaries filled with argon at a pressure of 0.25–0.5 Torr in the SIGNAL electrophysical facility. The experimental data are interpreted via computer simulations of the magnetohydrodynamics and level-by-level ion kinetics of an argon plasma. The results obtained indicate that soft X-ray laser pulses with a photon energy of 26.4 eV and duration of 1–2 ns are generated ≈33 ns after the beginning of the discharge current pulse.     

Effect of the direction of a preionization current on X-ray emission from a capillary discharge plasma

The effect of the direction of a preionization current on the generation of 469-Å X-ray emission from the plasma of a fast capillary discharge in argon was studied experimentally in the SIGNAL facility (the discharge current I = 25–40 kA and the current rise rate dI/dt ～ 10¹² A/s). The experiments were performed with 3.1-mm-diameter 157-mm-long ceramic capillaries filled with argon at a pressure of 0.2–1.0 Torr.     

Diagnostics of fast processes in laser plasmas after the irradiation of low-density media in the mishen facility

New experimental data on the laser irradiation of low-density porous materials in the Mishen facility are presented and discussed. A wide set of optical and X-ray diagnostics was used to analyze the physical processes in porous media with different microstructures and specific densities of 1–30 mg/cm³ exposed to laser pulses with λ=1.054 µm, τ=3 ns, and I=10¹³–10¹⁴ W/cm². The features of laser absorption and scattering and the processes of energy transfer in porous media were investigated for different average densities, thicknesses, and microstructures of the targets and different incidence angles of the laser beam. It was found that the material microstructure (chaotic or quasi-ordered) significantly affected the formation and dynamics of a plasma produced inside the irradiated samples that model the components of the advanced targets used in inertial confinement fusion research.     

Interferometric measurements of the plasma density at the Z-pinch periphery in the angara-5-1 facility

Knowledge of spatial mass distribution is important for understanding the physics of implosion of megaampere-current wire arrays. The paper presents results from studying the electron density distribution at the periphery of a tungsten wire array near the instant of maximum compression by using laser interferometry at λ=0.69 µm. It is found that, at the instant of maximum compression (～100 ns after the beginning of the discharge), the estimated maximum local electron density inside the wire array reaches ～10¹⁸ cm^?3 at a distance of 0.3–3 mm from the initial wire positions. Assuming the average tungsten ion charge to be 10, the local linear mass density in this region turns out to be 3 µg/cm, which amounts to about 10% of the total linear mass density of the liner. A fraction of the generator current flows through this plasma. The duration of the soft X-ray pulse is 5–8 ns, which indicates the achievement of a fairly high compression ratio.     

Optical characteristics of the plasma of a glow discharge in a He/H2O mixture

The emission from the plasma of a steady-state electric discharge in a He/H₂O mixture in the wavelength range 130–670 nm is investigated. It is shown that, at a water vapor partial pressure of P=2.0–2.5 kPa, the discharge mainly emits within the range 306–315 nm. The emission consists of an OH (A-X; 0-0) 307.4-nm narrow peak and a broad band with a maximum at λ_max=309.1 nm. As the partial pressure of water vapor decreases to 50–150 Pa, VUV emission at wavelengths of λ=186, 180, and 157 nm becomes dominant. In the visible region, H_α 656.3-nm and H_β 486.1-nm spectral lines and HeI lines in the range 447.1–667.8 nm, which are of interest for diagnosing the plasma, prevail. The intensities of the main bands and spectral lines are determined as functions of the helium partial pressure and discharge current.     

Measurements of neutron emission from a Z-pinch constriction

Results are presented from measurements of neutron emission generated during discharges with current amplitudes of up to 3 MA and a current rise time of ～100 ns through profiled loads 10 mm in height and 4–5 mm in diameter. The experiments were performed with the S-300 eight-module high-power generator. To enhance the effect of energy accumulation, a≤1-mm-diameter neck was made in the central region of the load. An agar-agar foam of mass density 0.1 g/cm³ with an additive of deuterated polyethylene was used as a plasma-forming material. The formation of a hot plasma in the Z-pinch constriction was accompanied by the emission of soft X-ray (E = 1–10 keV), hard X-ray (E ≥ 30 keV), and neutron pulses with a minimum pulse duration of ≤10 ns. The neutron energy measured by the time-of-flight technique in three directions relative to the load axis (0°, 90°, and 180°) was found to be 2.5 ± 0.3 MeV, which corresponds to the dd reaction. The total neutral yield during the development of one constriction with a characteristic size of 100 μm attained 10⁸ neutrons per pulse.     

Measurements of the parameters of a condensed deuterated Z-pinch on the angara-5-1 facility

Results are presented from measurements of the parameters of high-temperature plasma in the Z-pinch neck formed when a current of up to 3.5 MA flows through a low-density polymer load. To enhance the effect of energy concentration, a deuterated microporous polyethylene neck with a mass density of 100 mg/cm³ and diameter of 1–1.3 mm was placed in the central part of the load. During the discharge current pulse, short-lived local hot plasma spots with typical dimensions of about 200–300 μm formed in the neck region. Their formation was accompanied by the generation of soft X-ray pulses with photon energies of E > 0.8 keV and durations of 3–4 ns. The plasma electron temperature in the vicinity of the hot spot was measured from the vacuum UV emission spectra of the iron diagnostic admixture and was found to be about 200–400 eV. The appearance of hot plasma spots was also accompanied by neutron emission with the maximum yield of 3 × 10¹⁰ neutrons/shot. The neutron energy spectra were studied by means of the time-of-flight method and were found to be anisotropic with respect to the direction of the discharge current.     

Spatial structure of dimeric a genetically engineered variant of green fluorescent protein EGFP-K162Q in the P61 crystal space group

The spatial structure of dimeric green fluorescent protein EGFP-K162Q with MDELYK (EGFPv) C-terminal deletion has been assigned in the P6₁ space group with resolution 1.34 Å by X-ray diffraction analysis. The results have been compared with X-ray diffraction data of monomeric EGFP (green biomarker with enhanced photophysical properties) assigned in another crystal space group, P2₁2₁2₁, with resolution 1.50 and 1.35 Å. Subunits in the EGFPv dimeric structure are located at 75° angle with the contact area ～800 Ų. The dimeric framework is stabilized by the six hydrogen bonds and central hydrophobic core of six residues. The root-mean-square deviation value for C^α atoms in 3–230 residues of the P6₁ and P2₁2₁2₁ crystal structures is 0.55 Å. The differential characteristics of EGFPv-P6₁ structure, compared to that of P2₁2₁2₁, is a noticeably different orientation of the Glu222 side chain, and a new conformation of the 155–159 loop fragment, characterized by deviations among the C^α atoms of superimposed structures reaching 4.6 Å for Lys156 and 5.5 Å for Lys158.     

A source with a 1013 DT neutron yield on the basis of a spherical plasma focus chamber

Results from preliminary experimental research of neutron emission generated by a spherical plasma focus chamber filled with an equal-component deuterium-tritium mixture are presented. At a maximum current amplitude in the discharge chamber of ～1.5 MA, neutron pulses with a full width at half-maximum of 75–80 ns and an integral yield of ～1.3 × 10¹³ DT neutrons have been recorded.     

Experimental investigation of the shock wave in a fast discharge with cylindrical geometry

The work is devoted to the registration and the study of the properties of cylindrical shock waves generated in the fast discharge (dI/dt ～ 10¹² A/s) inside the ceramic tube (Al₂O₃) filled by argon at pressures of 100 and 300 Pa. The shock wave appears at the inner wall of the insulator and moves to the discharge axis with a velocity of about (3?4) × 10⁶ cm/s with subsequent cumulation. The plasma behind the front is heated enough to produce radiation in the vacuum ultraviolet (VUV) region, which makes it possible to study its structure by means of a pinhole camera with a microchannel plate detector. The time resolution of the registration system was 10 ns. The analysis of VUV spectra of the plasma shows that the electron temperature behind the shock wave front is about several eV; after the moment of cumulation, its temperature increases to 20–30 eV.     

Optical diagnostics of lead and PbGa2S4 layered crystal laser plasmas

Laser plasmas produced at the surfaces of lead and a PbGa₂S₄ layered crystal irradiated by a neodymium laser with λ=1.06 μm, pulse duration τ=20 ns, and intensity W=(1–2)×10⁹ W/cm² are studied using optical diagnostics. It is shown that, in a lead plasma, the most intense (characteristic) lines are the PbI 405.7-nm, PbI 368.3-nm, PbI 364-nm, and PbII 220.4-nm lines. In a layered crystal plasma, the emission spectrum is an aggregation of the most intense PbI and GaI lines, whereas sulfur lines are absent. The bottlenecks of the recombination of the ionic and atomic components of the lead and PbGa₂S₄ crystal plasmas are determined. The average propagation velocity of the lead laser plume is 18–20 km/s. A comparative analysis of the emission dynamics of PbI and GaI lines in the laser plasmas of these metals and in the plasma of a PbGa₂S₄ crystal is carried out. The results obtained are important for the optical diagnostics of the plasmas of leadand gallium-containing crystals and for the optimization of laser deposition of the thin films of these substances. __________ Translated from Fizika Plazmy, Vol. 27, No. 7, 2001, pp. 658–663. Original Russian Text Copyright ? 2001 by Shuaibov, Dashchenko, Shevera.     

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.     

The dynamics of and radiation from a copper-wire corona in a megaampere Z-pinch

Evolution of the extreme ultraviolet (XUV) and soft X-ray (SXR) emission in the 50-to 2000-eV photon energy range from a plasma corona formed by loading a relatively thick Cu wire (with an initial diameter of 120 µm) was observed in a Z-pinch discharge with a maximum current of 2 MA and current rise time of 100 ns. A diagnostic complex consisting of a five-channel SXR polychromator, a four-frame X-ray pinhole camera, and a mica crystal spectrograph shows that double-humped emission pulses in the XUV and SXR spectral ranges are generated 70–130 ns after the onset of the discharge current. The total energy of the pulses is 5 kJ, and the maximum power is 60 GW. A part of the observed kiloelectronvolt X-ray emission from three to five spots with diameters of 1–2 mm consists of the Cu K-and L-shell lines.     

Temporal Modulation of Sodium Current Kinetics in Neuron Cells by Near-Infrared Laser

Near-infrared laser provides a novel nerve stimulation modality to regulate the cell functions. Understanding its physiological effect is a prerequisite for clinic laser therapy applications. Here, the whole-cell sodium (Na) channel kinetics of neuron cell was employed to determine the temporal roles of infrared laser. The Na currents were elicited by electrical pulses that were synchronized at the rising and falling edges of the 980 nm laser pulses, respectively, to investigate the different infrared effect on cell functions. The time constants of activation (τ _m) and inactivation (τ _h) kinetics were extracted from fitting of the Na current (m³h) according to the Hodgkin–Huxley (HH) model. By comparing the time constants without and with the laser irradiation, we obtained that laser pulses changed the Na current kinetics by accelerating τ _h-phase and slowing down τ _m-phase at the beginning of the laser pulse, whereas both phases were accelerated at the end of the pulse. After relating the ratios of the time constants to the temperature characteristics of Na channel by Q ₁₀, we found that the accelerating in Na current kinetics could be related to the average temperature of extracellular solution in the corresponding time span by choosing Q ₁₀ = 2.6. The results of this study demonstrated that there was a positive correlation between the acceleration of the Na current kinetics and increases in temperature of the extracellular solution.     

Metal—phenoxyalkanoic acid interactions. Part 14. The crystal and molecular structures of diaquabis(4-fluorophenoxyacetato)copper(II) bis(4-fluorophenoxyacetic acid)dihydrate and tetra-μ-(4-fluorophenoxyacetato-0,0′)-bis[(2-aminopyrimidine)copper(II)]

The crystal structures of two copper(II) complexes of 4-fluorophenoxyacetic acid (4-FPAH) have been determined by X-ray diffraction. [Cu(4-FPA)₂(H₂O)₂]·2(4-FPAH)·2H₂O (1) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 14.808(2), b = 9.832(2), c = 6.847(2) Å, α = 87.77(2), β = 98.41(2), γ = 112.33(2)° and was refined to a residual of 0.038 for 1697 ‘observed’ reflections. The coordination sphere in this complex is tetragonally distorted octahedral comprising two waters [CuO, 1.940(3) Å], two unidentate carboxylate oxygens [CuO, 1.942(2) Å] and two ether oxygens [CuO, 2.471(2) Å]. Two adducted [4-FPAH] acid molecules are linked to the un-coordinated oxygens of the acid ligands by hydrogen bonds [2.547(4) Å]. [Cu₂(4-FPA)₄(2-aminopyrimidine)₂] (2) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 12.688(2), b = 11.422(2), c = 7.951(1) Å, α = 78.74(1), β = 107.51(1), γ = 75.78(1)°, and was refined to a residual of 0.042 for 2683 ‘observed’ reflections. (2) is a centrosymmetric tetracarboxylate bridged dimer with four similar CuO (equatorial) distances [1.967–1.987 Å; 1.977(3) Å mean] and the axial position occupied by the hetero nitrogen of the 2-aminopyrimidine ligand [CuN, 2.176(3) Å]. The Cu---Cu separation is 2.710(1) Å. Crystal data are also presented which confirm the isostructurality of complex (2) with [Cu₂(phenoxyacetate)₄(2-aminopyrimidine)₂], the Co^II, Mg^II and Mn^II4-fluorophenoxyacetate complexes with their phenoxyacetic and 4-chlorophenoxyacetic acid analogues, and of Cd^II4-fluorophenoxyacetate with Cd^II and Zn^II phenoxyacetates.     

EUV spectroscopy of plasmas created in the final anode-cathode gap of the Z-Machine high-current pulsed generator (SNL)

The effect of short-circuit across the final anode-cathode gap of powerful pulsed current generators could hamper efficient power delivery to the Z-pinch plasma. To study this effect, a novel EUV diagnostics of plasmas created in the final section of the transmission line (the anode-cathode gap near the main load) of the Z-Machine high-current generator (Sandia National Laboratories, United States) was developed. The work included developing spectroscopic instruments, theoretical and experimental studies of EUV spectra of iron ions in well-diagnosed laser-produced plasmas, and a comparison of these spectra with those of plasmas created in the final anode-cathode gap of the transmission line. The EUV spectra of highly charged Fe ions in the spectral range λ ～ 20–800 Å were investigated. In experiments performed at Sandia National Laboratories, spectra of FeXIII-FeXVII ions were observed. A comparison of the measured and calculated spectra shows that the electron plasma temperature in the anode-cathode gap is T _e ～ 200 eV.     

Space-charge-limited current in a plane vacuum diode discharged by an electron current pulse

An unsteady discharge of a relativistic vacuum diode is studied analytically. The amplitude and rise time of the discharge current pulse are determined as functions of the input parameters of the problem. It is found that, in a nonrelativistic limit, the maximum attainable amplitude of the discharge current pulse is equal to J_Alim = 9/4J_CL, where J_CL is the vacuum-diode limiting current prescribed by the 3/2 law. The parameters of the dipole moment of the layer formed above the grid anode are found in the nonrelativistic limit.     

Three‐dimensional structure,binding, and spectroscopic characteristics of the monoclonal antibody 43.1 directed to the carboxyphenyl moiety of fluorescein

Unlike other known anti‐fluorescein antibodies, the monoclonal antibody 43.1 is directed toward the fluorescein's carboxyl phenyl moiety. It demonstrates a very high affinity (K_D ～ 70 pM) and a fast association rate (k_on ～ 2 × 10⁷ M^?1 s^?1). The three‐dimensional structure of the Fab 43.1—fluorescein complex was resolved at 2.4 Å resolution. The antibody binding site is exclusively assembled by the CDR loops. It is comprised of a 14 Å groove‐shaped entrance leading to a 9 Å by 7 Å binding pocket. The highly polar binding pocket complementary encloses the fluorescein's carboxyphenyl moiety and tightly fixes it by multiple hydrogen bonds. The fluorescein's xanthene ring is embedded in the more hydrophobic groove and stacked between the side chains of Tyr37_L and of Arg99_H providing conditions for an excited state electron transfer process. In comparison to fluorescein, the absorption spectrum of the complex in the visible region is shifted to the “red” by 23 nm. The complex demonstrates a very weak fluorescence (Φ_c = 0.0018) with two short lifetime components: 0.03 ns (47%) and 0.8 ns (24%), which reflects a 99.8% fluorescein emission quenching effect upon complex formation. The antibody 43.1 binds fluorescein with remarkable affinity, fast association rate, and strongly quenches its emission. Therefore, it may present a practical interest in applications such as molecular sensors and switches. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 234–243, 2016.     

An assessment of the cis-influence in coenzyme B12 Models. The structure of the mixed schiff-base/oxime complex: Aquo(3,9-dimethyl-2,10-diethyl-1,4,8,1 1-tetra-azaundeca-1,3,8,10-tetraen-11-ol-1-olato)(methyl)cobalt(III)hexafluorophosphate

The title compound is the first accurately determined structure in the general class of ‘Costa’ B₁₂ models. The data permit comparisons of structural results to other relevant B₁₂ models and the construction of a cis effect series.Crystal Data: C₁₄H₂₀CoF₆N₄O₃P, M = 504.4, monoclinic, space group P2₁/c, a = 14.316(3), b = 6.819(1), c = 22.741(5) Å and β = 99.91(2)°, V = 2186.9 ų, D_m = 1.52, Z = 4, D_c = 1.53 g cm^?3, μ(MoKα) = 9.2 cm^?1, λ(MoKα) = 0.7107 Å. Unit cell parameters were refined and intensity data collected on a CAD4 computer-controlled diffractometer, using graphite-monochromated MoKα radiation. A total of 5803 reflections were collected and corrected for Lorentz-polarization factor, 2802 independent reflections with I > 3σ(I) being used in the subsequent calculations.The CoO bond length to the axial water is 2.102- (3) Å. This value places the Costa model structural cis influence as being comparatively close to corrin based systems, somewhat greater than cobaloximes and definitely lower than Schiff-base complexes.     

Memory effect in the ignition of a low-pressure glow discharge in nitrogen in a long discharge tube

Results are presented from experimental studies of breakdown and the initial stage of a discharge in a long tube (with an interelectrode distance of 40 cm and a diameter of 2.8 cm) at a pressure of ～1 Torr and pulse discharge current of ～10 mA. Breakdown was produced by positive voltage pulses with a linearly growing leading edge with a steepness of dU/dt ～ 10⁶–10⁸ V/s. The time interval between pulses was varied from τ = 0.5 ms to 1 s, the pulse duration being 10 ms. The work was aimed at studying the memory effect of the discharge gap, namely, the influence of the previous pulse on the breakdown characteristics of the next one. In the experiments, the breakdown voltage was measured at different values of dU/dt and τ. It was found that the memory effect was absent at τ ～ 1 s. At the same time, an increase in the breakdown voltage with increasing dU/dt was observed. In the range of τ ≈ 50–200 ms, the breakdown voltage also did not depend on τ, but the memory effect took place. The memory effect in this case consisted in that the breakdown voltage decreased with increasing dU/dt, so that, at dU/dt ～ 10⁷ V/s, the breakdown voltage was two times lower than in the case of τ ～ 1 s. For τ ～ 1–10 ms, the memory effect manifested itself in that the breakdown voltage depended on τ: it could either decrease (the “normal” effect) or increase (the “anomalous” effect) with increasing τ. Breakdown of the discharge gap was preceded by the propagation of an ionization wave, except for the case of small τ values in the domain of existence of the anomalous effect. Estimates allowing one to qualitatively explain the experimental results are made.