Generation of K-shell radiation in a double shell plasma linear with a microsecond current generator

Experiments on the generation of K-shell radiation in a double-shell neon liner with a microsecond current generator (τ≈1 μs, I _max=380 kA) are described. The yield of neon K-shell radiation attains 50–80 J per pulse. For the given current amplitude, such a radiation yield could be expected at a rise time as low as τ≈100 ns. Such a high radiation efficiency may be attributed to the sharpening of the front of the inner-shell current pulse because of the detachment of the outer shell from the electrode. __________ Translated from Fizika Plazmy, Vol. 27, No. 11, 2001, pp. 1003–1008. Original Russian Text Copyright ? 2001 by Chaikovsky, Sorokin.     

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.     

Photolysis of total histone and pBr-322 plasmid DNA in the ultraviolet vacuum region of the spectrum

The action of VUV and far UV (lambda greater than 240 nm) radiation of aqueous solutions of total histone by means of electrophoresis method is compared. By VUV photolysis the more effective destruction of HI and HIA histone fractions is determined. It may be explained by interaction of total histone with water radicals (H, OH) formed by VUV photodissociation (indirect mechanism). By VUV irradiation of plasmid pBR-322 DNA in aqueous solutions the indirect action mechanism of single strand breaks in DNA is established.     

Study of the plasma in a preformed Z-pinch constriction

The development of a preformed constriction in cylindrical agar-agar loads at currents of up to 3 MA is studied experimentally. The loads 3–5 mm in diameter have a mass density of 0.1 g/cm³ and are filled with different materials. Due to the implosion of the constriction to a minimum size of 40–70 μm, a hot dense plasma (with the electron density n _e=10²² cm⁻³, electron temperature T _e=0.8–1.5 keV, and ion temperature T _i=3–12 keV) is produced. It is found that the ion temperature substantially exceeds the electron temperature. The lifetime of the high-temperature plasma determined from the FWHM of a soft X radiation (SXR) pulse is shorter than 5 ns, the radiation power of photons with energies of ≥1 keV is higher than 0.5×10¹⁰ W, and their total energy attains 50 J. High-speed photography in the VUV, SXR, and optical spectral regions indicates the protracted generation of the high-temperature plasma. Calculations by the two-dimensional ideal MHD model of the Z-pinch show that the most important consequence of the protracted plasma generation in the constriction region is that the current is intercepted by a freshly produced plasma. In the course of plasma generation, the current near the axis inside the region of radius 50 μm is at most one-half of the total current. After the plasma generation comes to an end, almost the entire current is concentrated in this region for several nanoseconds; this process is accompanied by a sharp increase in the plasma temperature. __________ Translated from Fizika Plazmy, Vol. 27, No. 12, 2001, pp. 1101–1110. Original Russian Text Copyright ? 2001 by Bakshaev, Blinov, Vikhrev, Gordeev, Dan’ko, Korolev, Medovshchikov, Nedoseev, Smirnova, Tumanov, Chernenko, Shashkov.     

Multichannel vacuum arc discharge used for Z-pinch formation

Results are presented from experimental studies of the implosion dynamics and radiative characteristics of an aluminum Z-pinch formed from a plasma shell (PS). The PS with an initial diameter of 4 cm was produced with the help of a multichannel vacuum arc discharge and formed due to the evaporation of the electrode material in ten parallel arc discharges. The PS composition depended on the electrode material in the arc discharge. The described experiments were performed with aluminum electrodes. The total arc current was 80 kA. The PS implosion was provided by an IMRI-5 high-current generator with a current amplitude of 450 kA and rise time of 500 ns. The PS implosion resulted in the formation of a 0.2-cm-diameter plasma column with an electron temperature of 700?C900 eV and average ion density of (5?C8) × 10¹⁷ cm^?3. The maximum radiation power per unit length in aluminum K-lines reached 300 MW/cm, the duration of the radiation pulse being 20 ns.     

Compact optical cell system for vacuum ultraviolet absorption and circular dichroism spectroscopy and its application to aqueous solution sample

We have designed a compact optical cell for studying the absorption and circular dichroism (CD) of a solution sample in the vacuum ultraviolet (VUV) region using a temperature control unit. The cell size was 34 mm in diameter and 14 mm in length. Such compactness was obtained by coating the VUV scintillator onto the outside of the back window. Because this scintillator converts the transmitted VUV light to visible light, the outside of this cell is operated under atmospheric pressure. The temperature of the sample solution was maintained in the range of 5 degrees C to 80 degrees C using a temperature control unit with a Peltier thermoelectric element. Changes in the sample temperature were observed by monitoring the absorption intensity of water. Through the study of VUV-CD spectra of ammonium camphor-10-sulfonate aqueous solutions and the transmitted spectrum of an empty cell, it was concluded that this cell unit has sufficient performance for use in VUV spectroscopy.     

Gas-puff liner implosion in the configuration with helical current return rods

Results of experiments with double-shell gas-puff liners carried out on a high-current MIG generator (2 MA, 80 ns) are presented. To stabilize the process of liner implosion and increase the efficiency of energy transfer from the generator to the liner plasma, a current return in the form of a multifilar helix was used. The effect of the configuration of the current return on the parameters of the generated pulses of argon and neon K-shell radiation (with photon energies of 3–5 and 0.9–1.5 keV, respectively) and the neutron yield from a deuterium liner were studied.     

常春藤在室内生长适宜光照范围的研究

研究了常春藤(Hedera helix)适宜生长的光照范围问题。根据光的分布,选择房间内具有代表性的光区进行栽培试验。在18~28℃,RH31%~70%条件下。经栽培80 d后,用LI-6400测定其不同光强下的光合特性,计算光补偿点、光饱和点、最大净光合速率。同时测定不同试验区的叶面积、叶片数的生长量。结果表明:常春藤在18~28℃及RH31%~70%室内条件下,光照为大于3.1至小于834.3 μmol·m^-2·s^-1(155~41 715 lx)可以生长。     

Current scaling for the radiative characteristics of a micropinch discharge

The absolute VUV and soft X-ray (hν > 100 eV) yield from a micropinch discharge is measured for a fixed current of 150 kA. The current scaling in the range of 30–250 kA is found for a number of the discharge parameters: the VUV and soft X-ray yield, the electron temperature, the effective temperature of suprathermal electrons, and the energy of bremsstrahlung emission from thermal electrons. The experimental data are in good agreement with the simulations performed by using the model of radiative collapse in fast Z-pinches in plasmas of high-Zelements.     

Dynamics of an Al wire corona of a megaampere Z-pinch

It is shown that the development of instabilities in a Z-pinch plasma formed by loading a relatively thick Al wire (an initial diameter of 120 μm and a maximum discharge current of 2–3 MA) is slowed down due to the high plasma density in the wire corona. A cylindrically symmetric, regular, and stable corona surrounding the wire contains a helical formation with a dense, cold, and magnetized plasma. X-ray pulses with a photon energy of several keV and an FWHM duration of 10–20 ns are generated by a few imploded neck structures in the pinch phase of the corona evolution (70–100 ns after the current onset). The main part of X radiation emitted by individual bright spots in the photon energy range 1.5–2.4 keV (up to 40 J at a peak power of 4 GW) consists of the continuum and the bound-bound transition radiation from H-and He-like Al ions. A possible scenario for the axial magnetic field evolution during an X-ray pulse is outlined. __________ Translated from Fizika Plazmy, Vol. 28, No. 4, 2002, pp. 329–336. Original Russian Text Copyright ? 2002 by Kubeš, Renner, Krousky, Kravárik, Bakshaev, Blinov, Chernenko, Gordeev, Dan’ko, Korolev, Shashkov.     

A Study of the Ultraviolet Radiation of Hybrid X-Pinches

Plasma Physics Reports - The results of an experimental study of hybrid X-pinches (HXPs) as sources of vacuum ultraviolet (VUV) radiation within the wavelength range of λ < 2000 Å...     

Laser desorption 7.87 eV postionization mass spectrometry of antibiotics in Staphylococcus epidermidis bacterial biofilms

This paper describes the development of laser desorption 7.87 eV vacuum UV (VUV) postionization MS to detect antibiotics within intact bacterial colony biofilms. As >99% of the molecules ejected by laser desorption are neutrals, VUV photoionization of these neutrals can provide significantly increased signal as compared to the detection of directly emitted ions. Postionization with VUV radiation from the molecular fluorine laser single photon ionizes laser desorbed neutrals with ionization potentials below the 7.87 eV photon energy. Antibiotics with structures indicative of sub-7.87 eV ionization potentials were examined for their ability to be detected by 7.87 eV laser desorption postionization MS. Tetracycline, sulfadiazine, and novobiocin were successfully detected neat as dried films physisorbed on porous silicon oxide substrates. Tetracycline and sulfadiazine were then detected within intact Staphylococcus epidermidis colony biofilms, the former with LOD in the micromolar concentration range.     

Synchrotron radiation circular dichroism of various G‐quadruplex structures

Here we report synchrotron radiation circular dichroism spectra of various G‐quadruplexes from 179 to 350 nm, and a number of bands in the vacuum ultraviolet (VUV) are reported for the first time. For a tetramolecular parallel structure, the strongest band in the spectrum is a negative band in the VUV at 182 nm; for a bimolecular antiparallel structure with diagonal loops, a new strong positive band is found at 190 nm; for a bimolecular parallel structure with edgewise loops, a strong positive band at 189 nm is observed; and for a self‐folded chair‐type structure, the strongest band in the spectrum is a positive band at 187 nm. For the tetramolecular parallel structure, the CD signals at all wavelengths are dominated by contributions from quartets of G bases, and the signal strength is approximately proportional to the number of quartets. Our experiments on well‐characterized G‐quadruplex structures lead us to question past attributions of CD signals to helix handedness and G quartet polarity. Although differences can be observed in the VUV region for the various quadruplex types, there do not appear to be clear‐cut spectral features that can be used to identify specific topological features. It is suggested that this is because a dominant positive band in the VUV seen near 190 nm in all quadruplex structures is due to intrastrand guanine–guanine base stacking. However, our spectra can serve as reference spectra for the G‐quadruplex structures investigated and, not least, to benchmark theoretical calculations and empirical models. © 2009 Wiley Periodicals, Inc. Biopolymers 93: 429–433, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Synchrotron radiation circular dichroism spectroscopy applied to metmyoglobin and a 4-alpha-helix bundle carboprotein

The novel technique, synchrotron radiation-based circular dichroism (SR-CD), has been applied to the study of metmyoglobin and a carboprotein (carbohydrate-based peptide with protein tertiary structure) with 4-alpha-helix bundle structure, as well as a carbopeptide (carbohydrate-based peptide) with a truncated peptide sequence. The use of synchroton radiation (SR) enabled circular dichroism (CD) measurements in the vacuum ultraviolet (VUV) down to 168 nm in D(2)O and 160 nm in 2,2,2-trifluoroethanol (TFE). The band shape in the CD spectra in the low wavelength region was studied, comparing samples with two types of alpha-helical tertiary structure, namely the globin fold and the 4-alpha-helix bundle motif. No significant differences were found between the CD spectra of the alpha-helical samples (metmyoglobin and carboprotein) in D(2)O solution. The use of 2,2,2-TFE (TFE) as solvent clearly alters the VUV CD but the two samples have very similar CD spectra. The solvent-induced denaturing of metmyoglobin in TFE was observed using absorption and CD spectroscopy of the Soret band, with results indicating heme release. The VUV spectrum of TFE-denatured metmyoglobin exhibits dramatic differences in comparison with previous studies of the native enzyme in aqueous solution. The implications of this observation are discussed.     

Breakdown in helium in high-voltage open discharge with subnanosecond current front rise

Investigations of high-voltage open discharge in helium have shown a possibility of generation of current pulses with subnanosecond front rise, due to ultra-fast breakdown development. The open discharge is ignited between two planar cathodes with mesh anode in the middle between them. For gas pressure 6 Torr and 20 kV applied voltage, the rate of current rise reaches 500 A/(cm² ns) for current density 200 A/cm² and more. The time of breakdown development was measured for different helium pressures and a kinetic model of breakdown in open discharge is presented, based on elementary reactions for electrons, ions and fast atoms. The model also includes various cathode emission processes due to cathode bombardment by ions, fast atoms, electrons and photons of resonant radiation with Doppler shift of frequency. It is shown, that the dominating emission processes depend on the evolution of the discharge voltage during the breakdown. In the simulations, two cases of voltage behavior were considered: (i) the voltage is kept constant during the breakdown; (ii) the voltage is reduced with the growth of current. For the first case, the exponentially growing current is maintained due to photoemission by the resonant photons with Doppler-shifted frequency. For the second case, the dominating factor of current growth is the secondary electron emission. In both cases, the subnanosecond rise of discharge current was obtained. Also the effect of gas pressure on breakdown development was considered. It was found that for 20 Torr gas pressure the time of current rise decreases to 0.1 ns, which is in agreement with experimental data.     

Laser radiation scattering from the wires and fibers of imploding arrays on the Angara-5-1 facility

A method is developed for measurements of laser radiation scattering by wires and fibers in different types of imploding arrays in the initial stage of plasma production at discharge currents per wire of up to 2 kA for aluminum arrays and up to 8 kA for tungsten arrays. The experiments were carried out on the Angara-5-1 facility at a current density in the wires of 10⁸ A/cm² and current growth rate of ～10¹³ A/s. It is found that the indicatrix of laser radiation reflected from the wires (fibers) in cylindrical and conical arrays is modified at currents of 0.1–10 kA per wire (fiber). The experimental data on the reflection and scattering of laser radiation from wires and fibers are compared with the results of numerical simulations of their electric explosion in vacuum. It is proposed that the change in the reflection indicatrix of laser radiation is caused by the onset of thermal instabilities. The typical size of density and temperature inhomogeneities on the wire surface is in a range of 10–20 μm, which probably results in a transition from specular to diffuse reflection of laser radiation. A simultaneous abrupt (over 2–3 ns) reduction in the reflection intensity from several wires of an array indicates a homogeneous distribution of the discharge current over the irradiated wires. This closes the issue of the quality of the contact between the wires and the electrodes. The obtained experimental information is of considerable importance for the development of numerical codes for simulations of the implosion of wire arrays and the refinement of the wire parameters in the initial stage of plasma production.     

Interaction of photons with molecules – cross-sections for photoabsorption, photoionization, and photodissociation

A survey is given of recent progress in measurements of photoabsorption, photoionization, and photodissociation cross-sections of molecules in the wavelength range of photons in the vacuum ultraviolet (VUV), where the optical oscillator-strengths of most molecules are predominantly distributed. Some remarks are presented on molecules in the condensed phase. Particular emphasis is placed on the current understanding of spectroscopy and dissociation dynamics of molecules in the superexcited states which are produced through the interaction of photons in this wavelength range. In the VUV range, most of the observed superexcited states are assigned to high-Rydberg states which are vibrationally (and/or rotationally), doubly, or inner-core excited, and converge to each of the ion states. Received: 2 September 1998 / Accepted in revised form: 10 September 1999     

Effect of Vacuum Ultraviolet Irradiation on Abiogenous Synthesis of Adenine Nucleotides in the Presence of Lunar Ground

Vacuum ultraviolet (VUV) radiation, a powerful energy source in free Space, have been established to promote synthesis of natural nucleotides. It is shown that lunar ground protects from destruction (up to 1.5–2.0% ) the nucleotides formed after VUV-irradiation of dry films (adenosine and inorganic phosphate). Identification and quantitative determination of the products of synthesis and destruction is performed by the method of high performance liquid chromatography. The following products of synthesis are found: 5'-AMP > 2'3'-cAMP > 2'-AMP > 3'5'-cAMP > 3'-AMP. The obtained results are discussed from the viewpoint of hypothesis about the Space (extraterrestrial) origin of biologically important compounds that were initial for evolution on the Earth.     

Kinetics of phyllosemiquinone oxidation in the Photosystem I reaction centre of Acaryochloris marina

Light-induced electron transfer reactions in the chlorophyll a/d-binding Photosystem I reaction centre of Acaryochloris marina were investigated in whole cells by pump-probe optical spectroscopy with a temporal resolution of ~5ns at room temperature. It is shown that phyllosemiquinone, the secondary electron transfer acceptor anion, is oxidised with bi-phasic kinetics characterised by lifetimes of 88±6ns and 345±10ns. These lifetimes, particularly the former, are significantly slower than those reported for chlorophyll a-binding Photosystem I, which typically range in the 5-30ns and 200-300ns intervals. The possible mechanism of electron transfer reactions in the chlorophyll a/d-binding Photosystem I and the slower oxidation kinetics of the secondary acceptors are discussed.     

Penning plasma based simultaneous light emission source of visible and VUV lights

In this paper, a laboratory-based penning plasma discharge source is reported which has been developed in two anode configurations and is able to produce visible and VUV lights simultaneously. The developed source has simultaneous diagnostics facility using Langmuir probe and optical emission spectroscopy. The two anode configurations, namely, double ring and rectangular configurations, have been studied and compared for optimum use of the geometry for efficient light emissions and recording. The plasma is produced using helium gas and admixture of three noble gases including helium, neon, and argon. The source is capable to produce eight spectral lines for pure helium in the VUV range from 20 to 60 nm and total 24 spectral lines covering the wavelength range 20–106 nm for the admixture of gases. The large range of VUV lines is generated from gaseous admixture rather from the sputtered materials. The recorded spectrum shows that the plasma light radiations in both visible and VUV range are larger in double ring configuration than that of the rectangular configurations at the same discharge operating conditions. To clearly understand the difference, the imaging of the discharge using ICCD camera and particle-in-cell simulation using VORPAL have also been carried out. The effect of ion diffusion, metastable collision with the anode wall and the nonlinear effects are correlated to explain the results.