Enhancement of X-ray emission in the side on direction in a Mather-type plasma focus

A 1.8 kJ Mather-type plasma focus (PF) for argon and hydrogen filling is examined. Two anode configurations are used. One is tapered towards the anode face, and the other is cylindrical but the face is cut at different angles. At optimum conditions, the system is found to emit Cu–Kα X-rays of about 1.6±0.1 J/sr in the side-on direction for argon filling, which is about 32% of the total X-ray emission. In 4π-geometry, maximum total X-ray yield and wall plug efficiency found are 26.4±1.3 J and 1.5± 0.1% respectively. The modified geometry may help to use the PF as a radiation source for X-ray diffraction.     

Effect of pre-ionization on Cu Kα emission from a small plasma focus

One of the most important factors for optimizing the X-ray emission from a plasma focus device is the use of pre-ionization before triggering the device. In this paper, we investigated the effect of pre-ionization on Cu Kα and total X-ray emission from a Mather-type plasma focus device. The Cu Kα and total X-ray yield is measured as a function of the deuterium-filling pressure by using PIN-diode detectors. The maximum Cu Kα emission is found to be 1.95 J for the α-source and 1.62 J without the α-source, with corresponding average efficiencies of 0.049 and 0.06% without and with the α-source, respectively. The maximum total X-ray yield in 4π geometry is estimated to be about 2.64 and 2.12 J, with corresponding efficiencies of about 0.08 and 0.064% with and without the α-source, respectively.     

Correlation of plasma electron temperature with neutron emission ina low-energy plasma focus

Correlation of neutron emission with plasma electron temperature in a low-energy (2.3 kJ) plasma focus is investigated. To determine the plasma temperature by continuum X-ray analysis, cobalt is selected as the filter, which discriminates the line radiation from the background impurities like carbon, nitrogen, and oxygen, or the copper of which plasma focus electrodes are made. For a pressure range of high neutron emission (1-4 mbar), the neutron yield is found to correlate with the plasma temperature. The highest temperature recorded is 5 keV at 2.5 mbar, the filling pressure for the highest neutron emission in this device     

Influence of Kr doping on neon soft X-rays emission in fast miniature plasma focus device

An investigation on the possibility of enhancement of soft X-ray (SXR) (900–1600 eV) emission from a fast miniature plasma focus (FMPF) device of 235 J (at 14 kV) storage energy through doping of operating gas was performed. Neon (Ne), the operating gaseous medium, was doped with krypton (Kr) in different volumetric ratios at various operating pressures ranging from 2 to 14 mbar. The 1% Kr doping increased the average optimum SXR emission efficiency from 0.47% to 0.6% without enhancing the hard X-ray (HXR) (>1600 eV) emission. The Kr doping influenced the major pinching characteristics such as focusing efficiency and time to pinch with consequential effect on X-ray emissions. Synchronous operation of the 4 pseudo-spark gap (PSG) switches was mandatory for efficient discharge current delivery to the electrodes. A drastic improvement in the pinching efficiency was obtained with replacement of old and worn out PSG switches with the new ones. Optical imaging of current sheath dynamics was performed using gated ICCD camera to verify the normal operation of the device after the PSGs replacement. A numerical simulation analysis on the 2 cm long stainless steel tapered anode, used in this study, was done to predict the maximum SXR emission efficiency and the peak operating gas pressure. An analysis on the amount of SXR fluence generated at the source position and the proportion of it reaching the target position is also reported.     

Explosive plasma-vortex optical radiation sources

The results of experimental study of explosive radiation sources based on pulsed injection of a cumulative plasma jet into atmospheric air are considered. The injection process is accompanied with intense vortex formation as well as the formation of a large-scale toroidal plasma vortex. High-power electromagnetic radiation in the optical range is generated due to shock-wave processes during deceleration of a plasma jet in air and plasma-chemical processes in the vortex. The temporal structure of a radiation pulse being generated contains components from the micro- and millisecond range. For a 20-g mass of the explosive charge, a peak radiation power of 300 kW/sr and an energy yield of 400–600 J/sr integrated over the emission spectrum are attained. The efficiency of conversion of the chemical energy of the explosive into radiation is 5.0–7.5%.     

Gas mixture effects on ion‐beam flux characteristics from dense plasma focus device: Investigation by the Vlasov–Maxwell equations and experiments

The Vlasov–Maxwell equations were numerically solved to calculate the ion‐beam flux from the plasma of argon and the plasma of mixtures of argon and neon. Some experiments were performed to measure the ion beam from the Amirkabir plasma focus (APF) device. The calculations have shown that the argon ion‐beam flux peaked up to 1.928 × 10³⁰ ions m^?2 s^?1 at the optimum pressure of 1.866 mbar while the neon‐argon mixture's ion‐beam flux reached a maximum of 4.301 × 10³⁰ ions m^?2 s^?1 for 15% neon admixture at the optimum pressure of 1.866 mbar. The calculated kinetic energy of the ion beam has shown a maximum value of 708.7 J for the mixture of 85% argon‐15% neon at the mentioned optimum pressure.     

Influence of sputtering pressure on the giant magnetoresistance and structure in Fe–Cu–Ni granular thin films

Composition, structure and giant magnetoresistance in Fe_xCu_yNi_z films prepared at different sputtering pressures were investigated. X-ray diffraction studies showed only Cu (1 1 1) peak from the Cu grain. The shifts in the d-spacing d₁₁₁ of Cu indicates a progressive substitution of Ni in the Cu lattice. Similar trends in d₁₁₁ of Cu observed for the samples prepared at different sputtering pressures indicate that the structural behaviour of the samples is nearly independent of the sputtering pressure. A significant enhancement of magnetoresistance (MR) for the samples sputtered at 0.001 mbar as compared to that sputtered at 0.02 mbar is attributed to the reduced role of residual gas impurities in the films upon lowering the sputtering pressure. An interesting observation is that the MR did not significantly decrease even with a large substitution of Ni in the Cu grains.     

Optimization of a Dielectric Barrier Discharge for Pulsed UV Emission of XeCl at 308 nm

A pulsed dielectric barrier discharge (DBD) has been investigated in a wide range of experimental conditions with the purpose of optimization for XeCl excimer radiation. For that the following operation parameters had been considered: four different lamps of coaxial geometry with gas gaps in the range of 1.3 ‐ 6.5 mm; gas mixtures of xenon and chlorine containing admixtures of 1%, 2% and 4% Cl₂ at total filling pressures between 5 mbar and 600 mbar; voltage rise times of 20 ‐ 50 ns and voltage amplitudes of up to 12 kV. A maximum radiation pulse energy of 1.8 µ J has been detected at 310 ± 10 nm with an estimated radiation decay by three orders of magnitude within about 5 µ s. It was shown that the minimization of the voltage rise time is essential for enhancing the radiation pulse energy. Furthermore a correlation between the discharge geometry and the optimum pressure for maximum radiation output was observed. The decay characteristics of the excimer emission provides evidence of the harpoon reaction being the main channel of XeCl formation under our operation conditions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of oxygen partial pressure on the structure and properties of Cu–Al–O thin films

We have studied the electrical and optical properties of Cu–Al–O films deposited on silicon and quartz substrates by using radio frequency (RF) magnetron sputtering method under varied oxygen partial pressure P_O. The results indicate that P_O plays a critical role in the final phase constitution and microstructure of the films, and thus affects the electrical resistivity and optical transmittance significantly. The electrical resistivity increases with the increase of P_O from 2.4 × 10^?4 mbar to 7.5 × 10^?4 mbar and afterwards it decreases with further increasing P_O up to 1.7 × 10^?3 mbar. The optical transmittance in visible region increases with the increase of P_O and obtains the maximum of 65% when P_O is 1.7 × 10^?3 mbar. The corresponding direct band gap is 3.45 eV.     

Reduced absorption of neon-like bromine X-ray laser radiation in helium

We have measured the absorption of the 19.47-nm neon like bromine (J=2–1) X-ray laser line in low-pressure helium. The experiment was motivated by the coincidence of this line with the low-absorption wing of an autoionizing transition in helium. We observe that, with 1 mbar of helium, the continuum background and another bromine X-ray laser line at 19.82 nm are strongly reduced, enhancing the relative strength of the 19.47-nm laser line. Increasing the helium pressure to 1.5 mbar makes the continuum virtually disappear, resulting in an almost monochromatic emission of the X-ray laser line. An estimate of the absorption cross section for the 19.47-nm line is given as ≈3.9×10^-19 cm² and for the nearby continuum as 0.9–1.3×10^-18 cm². Received: 8 March 1999 / Revised version: 26 April 1999 / Published online: 11 August 1999     

Growth of AgInSe<Subscript>2</Subscript> on Si(100) substrate by thermal evaporation technique

AgInSe₂ films were prepared by a thermal evaporation technique onto Si(100) substrates at a pressure of 10⁻⁵ mbar. Structural and optical properties of films deposited at 300 and 473 K have been investigated. The film composition was studied by energy dispersive analysis through X-rays. X-ray diffraction patterns indicate that AgInSe₂ films have chalcopyrite structure with strong preferred orientation in the (112) direction. Average vertical crystallite size of 25 nm was observed. The optical energy gaps of 1.20 and 1.90 eV were obtained due to the fundamental absorption edge and a transition originating from crystal field splitting, respectively. Field emission scanning electron microscopy shows loosely packed grains of spherical symmetry with some facets.     

Scope of plasma focus with argon as a soft X-ray source

The X-radiation emission from a low energy plasma focus with argon as a filling gas is investigated. Specifically, the attention is paid to determine the system efficiency for argon K-lines and Cu-K/sub /spl alpha// line emission at different filling pressures, and identify the radiation emission region. The highest argon line emission found at 1.5 mbar is about 30 mJ and the corresponding efficiency is 0.0015%. The same pressure is suitable for high Cu-K/sub /spl alpha// emission, which is about 70 mJ in 4/spl pi/ geometry and the system efficiency is 0.003%. The bulk of X-radiation is emitted from the region close to the anode tip, whereas some radiation emission takes place from the formed hot spots along the focus axis. These radiations are found suitable for backlighting in Al (1-1.56 keV) and Ti (2.9-4.96 keV) energy transmission bands.     

Shock-wave velocity of a femtosecond-laser-produced plasma

Fluorescence measurements have been used to characterize the velocity of atoms in a femtosecond-laser-produced plasma. Nanogram amounts of a copper sample were ablated by the focused radiation (λ=775 nm) of an all-solid-state laser. The laser was operated at a pulse rate of 10 Hz with an energy of 200μJ per pulse. The microplasma expanded into a defined argon atmosphere of pressures between 0.02 and 850 mbar. Atomic fluorescence was excited in the laser plume by a dye-laser pulse with the wavelength set to the line Cu I 282.4 nm. The narrowed beam of the dye-laser was directed into the plasma at different heights above the sample surface. The fluorescence radiation was measured with an échelle-spectrometer, equipped with an intensified-charge-coupled device as the detector. The velocity depends strongly on the pressure of the ambient atmosphere and the distance from the sample surface. The highest velocity found at an argon pressure of 0.02 mbar was 1.0×10⁶ cm s⁻¹.     

Influence of Cu doping on the microstructure,optical properties and photoluminescence features of Cd0.9Zn0.1S nanoparticles

Cd_0.9−xZn_0.1Cu_xS (0≤x≤0.06) nanoparticles were successfully synthesized by a conventional chemical co-precipitation method at room temperature. Crystalline phases and optical absorption of the nanoparticles have been studied by X-ray diffraction (XRD) and UV–visible spectrophotometer. XRD confirms the phase singularity of the synthesized material, which also confirmed the formation of Cd–Zn–Cu–S alloy nanocrystals rather than separate nucleation or phase formation. Elemental composition was examined by the energy dispersive X-ray analysis and the microstructure was examined by scanning electron microscope. The blue shift of absorption edge below Cu=2% is responsible for dominance of Cu⁺ while at higher Cu concentration dominated Cu²⁺, d–d transition may exist. It is suggested that the addition of third metal ion (Cu²⁺/Cu⁺) is an effective way to improve the optical property and stability of the Cd_0.9Zn_0.1S solid solutions. When Cu is introduced, stretching of Cd–Zn–Cu–S bond is shifted lower wave number side from 678 cm⁻¹ (Cu=0%) to 671 cm⁻¹ (Cu=6%) due to the presence of Cu in Cd–Zn–S lattice and also the size effect. The variation in blue band emission peak from 456 nm (∼2.72 eV) to 482 nm (∼2.58 eV) by Cu-doping is corresponding to the inter-band radiation combination of photo-generated electrons and holes. Intensity of red band emission centered at 656 nm significantly increased up to Cu=4%; beyond 4% it is decreased due to the quenching of Cu concentration.     

超短超强激光脉冲作用下的Mo等离子体X射线辐射(英文)

在SILEX-1激光器上,利用光子计数型CCD测量了超短超强激光束与高纯度Mo相互作用而产生的发射谱。实验发现, 在超短超强激光脉冲作用下, Mo等离子体辐射Kα X射线, 这一过程伴随很强的热辐射和轫致辐射。Mo等离子体Kα X射线辐射强度、 热辐射和轫致辐射随激光功率密度增加而增强。Using a Single photon counting CCD, X ray emission spectra of high purity Mo irradiated by ultra short and ultra intense laser pulse was firstly detected. The experiment was carried out with the SILEX 1 laser facility. The experimental results show that, for Mo target, characteristic K shell emission (Kα) is observed in the 0.23—2.32 J energy range in addition to a broadband bremsstrahlung background, and the X ray radiation intensity, thermal radiation and bremsstrahlung increase with enhancementofthe laser power density.     

Effective radius of adatoms/single atom of polycrystalline W nanotip in gas field ion source

A gas field ion source (GFIS) has several advantages such as high current density, low energy spread, and high brightness. In this study, Helium gas was used in a GFIS, generated using the field ionization and field evaporation processes. The (110) oriented three adatoms tip (TAT) and single atom tip (SAT) were prepared with its ion emission stability 9.8% and 10.1% by the nitrogen field-assisted etching, respectively. The TAT and SAT were reproduced throughout the field evaporation and nitrogen field-assisted etching along the same crystal axis with its brightness 2.6 × 10⁷ A/(m² sr) and 1.6 × 10⁸ A/(m² sr), respectively. The field emission electron beam effective radii for three adatoms and single atom were calculated to be 2.90 Å and 1.47 Å, respectively, by Fowler-Nordheim plot, in which the single atom size was especially shown to be quite in good consistency with an atomic radius of tungsten.     

Aperiodic multilayer mirrors for efficient broadband reflection in the extreme ultraviolet

Recent extreme ultraviolet sources using high-harmonic generation in a rare gas make new optics developments necessary. We report on the study and development of multilayer structures with efficient reflectivity in the 35–75 eV energy range. We have optimized, deposited and characterized two aperiodic broadband mirrors consisting of a Mo, Si and B₄C thin-film stack. We used the needle procedure in order to optimize mirror reflectivity. The magnetron sputter deposited multilayers have been calibrated and characterized using Cu K _α grazing incidence X-ray reflectometry. Reflectivity measured at near-normal incidence on a synchrotron radiation source reaches 12% with a full width at half maximum of nearly 40 eV. Experimental results are compared with theoretical simulation using available optical constants for Mo, Si and B₄C in this spectral range.     

Check of the scaling procedure of track structures of ionizing radiation in nanometric volumes

In nanodosimetry, the track structure of ionizing radiation is characterized by the probability distribution of the number of ionizations produced by an ionizing particle in a target volume. By Monte-Carlo simulations of the track structure, this so called ionization cluster size distribution can be determined for nanometric cylindrical water targets used as substitute for the radiation sensitive biological target, namely a DNA-segment of about 20 base pairs length. Measurements of ionization cluster size distributions are carried out in an ion-counting nanodosimeter filled with an appropriate working gas at low pressure. A scaling procedure was proposed by Grosswendt (2006) to derive an operating pressure depending on the working gas for which the measured ionization cluster size distribution becomes equivalent to the ionization cluster size distribution within a nanometric target of liquid water. This scaling procedure was previously tested by means of Monte-Carlo simulations and is now tested experimentally.Ionization cluster size distributions produced by mono-energetic proton and alpha particle beams in the energy range between 0.1 MeV and 20 MeV were measured at the accelerator facilities of the PTB. The working gases used in this experiment were C₃H₈ and N₂. According to the NIST databases for stopping power and mean ionization energy (NIST, 2009), equivalent cluster size distributions for protons and alpha particles should be obtained for pressures of 0.25 mbar C₃H₈ and 1.2 mbar N₂. Measurements reveal the best agreement with pressures of 0.425 mbar C₃H₈ and 1.2 mbar N₂ for protons and 0.46 mbar C₃H₈ and 1.2 mbar N₂ for alpha particles.     

Optical and IR studies on r.f. magnetron sputtered ultra-thin MoO3 films

Ultra-thin MoO₃ films were deposited onto glass and Si substrates by r.f. magnetron sputtering. The optical and IR properties of the films were studied in the range of 250 to 1000 nm and 400 to 1500 cm⁻¹, respectively. The optical transmission spectra show a significant shift in absorption edge. The energy gap of the films deposited at 373 K and 0.1 mbar was found to be 3.93 eV, and it decreases with increasing substrate temperature and decreasing sputtering pressure. The IR transmittance spectra shows strong modes of vibrations of Mo=O and Mo–O–Mo units of MoO₃ molecule. A significant change in energy gap and a shift in frequency of IR modes were observed in ultra-thin MoO₃ films.     

Low energy electronic spectroscopy of an infinite-layer cuprate: A resonant inelastic X-ray scattering study of CaCuO2

We report the results of Oxygen K-edge soft X-ray absorption and emission spectroscopy that was performed on an infinite-layer insulating cuprate thin film CaCuO₂. Experimentally obtained spectra are consistent with local density approximation calculations. X-ray absorption spectra show a close resemblance to spectra obtained from homologous single crystal cuprates. In addition to d–d excitations, X-ray emission spectra reveal the presence of Zhang-Rice singlet states in the infinite-layer CuO₂ planes. The question of whether the Zhang-Rice singlet features are masked by the O 2p main-band is addressed: it is possible to quantify the position of the Zhang-Rice singlet using emission intensity profiles. X-ray emission is demonstrated as a tool for understanding CuO₂ planar electronic correlation in the prototypical infinite-layer. The energy difference, 2.0 eV, between the oxygen main-band and the Zhang-Rice singlet band is found to match values obtained theoretically using established planar electronic correlation parameters.