A detector for imaging of explosions on a synchrotron radiation beam

Synchrotron radiation (SR) offers a unique chance to study the structure of a substance in fast processes. Since SR is emitted by electron bunches in a storage ring, the SR burst corresponding to a single bunch may be very short. Should a detector capable of detecting SR from a single bunch without mixing signals from different bunches be available, it is possible to obtain information on changes in the state of the material in a sample under investigation with a very high time resolution. A detector for imaging of explosions on an SR beam—DIMEX—has been developed by the Budker Institute of Nuclear Physics (Siberian Division of the Russian Academy of Sciences, Novosibirsk). This detector is a high-pressure ion-ization chamber with a strip readout at a pitch of 0.1 mm. The electron component of primary ionization is collected within 50 ns, which is substantially shorter than the orbital period of a bunch in the VEPP-3 storage ring (250 ns). The DIMEX is filled with a Xe—CO₂ mixture (3: 1) at an absolute pressure of 7 atm. The spatial resolution of the detector is ∼210 μm, and its efficiency for radiation with an energy of 20 keV is ≥50%. The dynamic range of the detector is ∼100, which allows one to measure the signal with an accuracy of ∼1%. In this case, the maximum flux of X-ray photons, at which the DIMEX operates in a linear region, is ∼10¹⁰ photons/(channel s). Today, the detector has been used in experiments aimed at studying evolution of the density in detonation waves and processes of nanoparticle production at the VEPP-3 storage ring by employing the small-angle X-ray scattering technique.     

Investigation of spectral resolution in a Czerny Turner spectrograph

This article describes a smiple and low-cost Czerny-Turner spectrograph capable to operate in spectral range from approximately 350–900 nm. A sine drive assembly was used for linearizing the wavelength scale. The wavelength and pixel position calibration problem have been solved using light sources with known wavelength emission lines, and a polynomial fitting method to find the relationship between diffraction wave-lengths and pixel numbers. The pixel resolution ∼0.015 nm/pixels and FWHM ∼0.1 nm at 170 μm entrance slit width are sophisticated enough to serve well in a research laboratory, yet is simple and inexpensive enough to be affordable for educational use.     

Ion processes in a liquid-xenon ionization chamber under high-intensity pulsed irradiation

The current of positive ions in a liquid-xenon ionization chamber was studied under intense pulsed irradiation of the chamber with bremsstrahlung from a microtron. The dose absorbed in xenon during a radiation pulse was varied from 0.1 to 1.3 × 10⁴ μGy. It has been revealed that, in the dependence of the current on the irradiation dose, a deviation from a simple linear dependence is observed at a pulse dose of ∼4 μGy (∼0.2D _cr). Calculations show that recombination is the main cause of such deviation. A space charge appearing in the chamber under high irradiation intensities leads to a decrease in the electric field. The manifestation of the effects of a space charge becomes substantial when the field in a certain part of the chamber drops almost to zero. Under particular irradiation conditions, the space charge manifested itself in this study beginning with doses in a pulse of ∼50 μGy. The joint effect of the recombination and the space charge resulted in a dependence of the type of i ∼ D ^1/3. The influence of the ion current on the energy resolution of the ionization spectrometer is calculated for γ quanta detected during intervals between irradiation pulses. It is shown that a substantial impairment of the resolution begins at doses appreciably lower than the critical dose. The influence of the ion current becomes greater, as the dimensions of the chamber increase.     

An experimental setup for studying neutron-neutron final state interaction on the neutron channel of the Moscow Meson Factory

A setup for measuring the singlet nn-scattering length in the n + d → p + n + n reaction is described. It is composed of a neutron hodoscope with an angular aperture of 12° and a scintillation detector for protons escaping at an angle of 90° with the beam direction. The exit angles and the energies of a proton and both neutrons are measured. The neutron energies are measured using the time-of-flight method. At a time resolution of ∼0.6 ns and a flight base of ∼5.5 m, the accuracy in measuring the neutron energy is ∼1% at an energy of ∼15 MeV. The dependence of the reaction yield on the relative energy of two neutrons is investigated. The neutron-neutron final-state interaction manifests itself as a peak in this distribution.     

The amplitude and current pulse duration of a supershort avalanche electron beam in air at atmospheric pressure

The results of experimental studies of the parameters (amplitude and duration) of a supershort avalanche electron beam (SAEB) generated in air at atmospheric pressure are presented. It is shown that the pulse duration of the beam current behind the foil from the entire area of the anode foil is larger than from small areas and depends on the cathode design. The number of electrons that are detected behind the 10-μm-thick Al foil is ∼6 × 10¹⁰ electrons, which corresponds to a SAEB amplitude of ∼100 A at a FWHM of the current pulse of ∼100 ps. An X-ray exposure dose per pulse of ∼1.8 mR was obtained using a 20-μm-thick copper foil. It was confirmed that the FWHM of a SAEB pulse is within ∼50 ps from small foil areas (with diameters of ∼7 mm or smaller).     

Cryogenic tilt table

We describe the design and development of a cryogenic tilt table that will be used to test the flight hardware for NASA’s Satellite Test of the Equivalence Principle (STEP). Our table can tilt the hardware around two axes and is part of a test bed that has 6-degree-of-freedom controllability. The goal was to build a tilt table with a resolution better than ∼5 μrad (1 arcsec). Our table consists of three aluminum plates. The outermost plate is attached to the cryogenic probe and is fixed. The middle and inner plates rest on the outer and middle plates, respectively, using knife edges and knife edge holders made of silicon nitride that are glued to the aluminum plates. A cryogenic tilt sensor was also developed and integrated with the table. The sensor consists of an electrically grounded copper cube hanging from a support, and is placed between two pairs of capacitive electrodes. Any motion of the cube caused by tilting is measured differentially using a Wheatstone bridge circuit. The table is connected to the bottom of a cryogenic probe. A voice coil actuator, located on top of the probe at room temperature, is used to create the necessary tilt. A thin fiber is used to connect the actuator and the table. The system is controlled using a dSPACE control card. A test of the table at cryogenic temperatures (4.5 K) and low pressure (1 μTorr) showed a noise level of ∼0.7 μrad (150 marcsec), which is nearly an order of magnitude better than the required resolution.     

Ultimate characteristics of an X-ray prism spectrometer

X-ray prism spectrometry schemes for experimental investigations of fast processes are considered. Diamond and beryllium prism dispersion parameters and special features of transmission spectra for crystal prisms are analyzed. It is shown that relative energy resolution E/ΔE at photon energies E ∼ 10 keV may reach 10³–10⁴ and the total working spectral band is ∼100 keV. This opens unique possibilities for measuring fine structures of single-shot absorption spectra for quasi-parallel beams and continuous monitoring of the fundamental and high-frequency harmonics of an X-ray free electron laser. Original Russian Text ? A.G. Tur’yanskii, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 4, pp. 150–158.     

Installation for air cleaning from organic impurities by plasma formed by barrier discharge of nanosecond duration

A prototype installation for air cleaning by plasma, which consists of a barrier-type discharge reactor and a high-voltage nanosecond-pulse supply generator, which is based on drift step recovery diodes, is considered. A stable corona-type barrier discharge was obtained at a 3-kHz supply-pulse repetition frequency. The discharge remained nonlocalized even at a small gas-discharge gap (∼6 mm) due to a short (∼25 ns) pulse duration, which allows a quite uniform effect on the air flow. The high rise rate (∼6 kV/ns) of the applied supply voltage pulses determines the high voltage amplitude (∼25 kV) at the reactor at the breakdown moment and allows maintenance of high electric-field intensity and a high intensity of plasma chemical processes. Thus, an electrical power lower than 8 W is required at the reactor input to produce 1 g of ozone per hour. The concentration of methylmercaptan in air during waste-water smell deodorizing at State Unitary Enterprise “Vodokanal of St. Petersburg” was reduced down to an allowable level of 0.5 mg/m³ at the electrical power consumption no higher than 0.25 W per cubic meter of air.     

Use of an CXP8 X-ray streak camera for measuring the time characteristics of X rays emitted by a laser plasma

The time dependence of the X-ray intensity from targets exposed to single-shot or successive picosecond laser pulses at the NEODIM facility was obtained by direct measurements. The measurements were taken using an CXP8 streak camera (produced by the Research Institute of Pulse Techniques) with a picosecond time resolution under different operating conditions of the facility. The observed X-ray pulses had a half-height duration of 15–50 ps and a rise time of 5 ps at a ∼1.5-ps duration of the effecting laser pulse. Under actual experimental conditions, it was ascertained that time dependences of the X-ray intensity could be recorded for more than 200 spatial elements on a single record at a sweep duration of 0.5 ns per frame and a time resolution of <5 ps.     

A new compact microwave spectroradiometer-ozonometer

A new-generation mobile microwave spectroradiometer intended for studying the Earth’s ozone layer is described. The device receives thermal radio-frequency emission of the stratospheric ozone at the frequency of its rotational transition (110 836 MHz) in a 240-MHz frequency band. The spectral resolution at the O3 line center is 1 MHz. The effective noise temperature of the uncooled receiver in the single-sideband mode is ∼2000 K. The ozonometer is equipped with a computer-aided data measurement, calibration, and preprocessing control system. The device is intended to obtain an ozone profile in a 20- to 60-km altitude interval within 15–20 min.     

A two-frequency pulse refractometer for measuring the electron density in tokamaks

An instrument for fringe-jumps free measurements of the electron concentration and estimations of the peaking factor of density distributions in magnetic confinement plasma devices with probing at frequencies close to the cutoff is described. The instrument is intended to perform measurements in a 5 × 10¹⁸–10²⁰ m⁻³ density range (while probing by the extraordinary wave) with time resolution ∼10 μs.     

An efficient cathode for generating an supershort avalanche electron beam in air at atmospheric pressure

The cathodes of accelerators intended for generating an ultrashort electron beam in air at atmospheric pressure were studied. A cathode allowing an increase in the amplitude of the beam current behind the foil by several times has been developed. The beam current amplitude obtained at a half-height pulse duration of ∼100 ps is ∼80 A.     

A nanosecond light source for scintillation-and Cerenkov-detector calibration

A nanosecond blue-light source with increased brightness is described. A light-emitting diode by NICHIA is used. The pulse shaper triggering the light-emitting diode is based on avalanche transistors. The number of photons per pulse is ∼10⁹ at a light-pulse duration of ∼2 ns.     

A laser ion-mobility spectrometer

The process of ion-packet broadening in a longitudinal laser spectrometer of ion mobility is studied. The contributions of the diffusion, Coulomb, and other broadening mechanisms are compared. The resolution of the developed spectrometer was measured (R ∼ 45) in atmospheres of both purified air and pure nitrogen. The dependence of the spectrometer resolution on the drift voltage was studied. The recorded spectra of a number of molecules of explosives with an extremely low pressure of saturated vapors indicate a high sensitivity of the developed spectrometer (no worse than 10⁻¹⁴ g/cm³). Original Russian Text ? G.E. Kotkovskii, I.L. Martynov, V.V. Novikova, A.A. Chistyakov, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 2, pp. 110–116.     

Spectromicroscopy of tribological films from engine oil additives. Part I. Films from ZDDP's

Antiwear films formed from pure neutral alkyl‐ and aryl‐ZDDP's, and a commercial ZDDP, have been studied with high resolution synchrotron‐based photoemission spectromicroscopy with a new instrument, MEPHISTO. Good P L‐edge XANES spectra have been taken on areas between 12 and 400 μm², and good images of phosphates and ZDDP have been obtained at ∼1 μm resolution on both smooth and rough steel. These spectra, and corresponding images, show immediately that both the chemistry and the morphology of the alkyl and aryl films are very different. The alkyl film contains a range of smaller and larger protective polyphosphate pads from a few to ∼25 μm² in area. We have shown that the chemistry of small and large pads are different. The large pads contain very long chain polyphosphate; while the smaller pads contain short chain polyphosphate. The aryl films contain ortho‐ or pyro‐phosphates, are much thinner and more uniform, with obviously more streaking from initial wear, and no obvious protective pad formation. Antiwear films generated from the commercial ZDDP, rubbed in base oil, show that the long chain polyphosphate is converted to ortho‐ or pyro‐phosphate, but the amount and distribution of phosphate does not change noticeably. The antiwear films are remarkably stable physically. This revised version was published online in July 2006 with corrections to the Cover Date.     

A radiation foil bolometer for measuring the energy losses of fast Z-pinches

A radiation foil bolometer intended for measuring radiation-energy fluxes and plasma flows in high-power pulsed plasma X-ray sources is studied. In the bolometer, the radiation or ion-flow energy is absorbed by a 13-μm-thick niobium foil preliminarily heated to T ≈ 1900 K by a quasi-constant current lasting 2 s. Radiation from the foil was fed through an 8-m-long light guide to a semiconductor photodetector. The sensitivity of the instrument obtained from the results of calibrations is 0.56 J/V cm². The time resolution of this technique (∼2.5 μs) is determined by the foil heating time. In experiments with megaampere Z-pinches, the time resolution attained allows detection of the radiation energy independently of the energy of expanding plasma flows. In this case, the photoelectric effect from X-rays and the conductivity of expanding plasma do not affect the operation of the radiation bolometer. The working capacity of the bolometer was demonstrated at the Angara-5-1 facility in experiments with high-current Z-pinches with a radiation output energy of 50–100 kJ/pulse. The measurements performed have shown that the energy flux density of plasma expanding in the direction perpendicular to the pinch axis is at most 5% of the energy flux density of soft X-rays.     

Characteristics and behavior of the electron beam of the MиH-1 accelerator in air

The electron-beam characteristics of the MиH-1 accelerator have been measured. At the output of the accelerating tube, the current-pulse amplitude is ∼1kA, duration ∼10ns, and maximal electron energy ∼600 keV. As the beam passes through the air, its diameter increases linearly with the distance varying from 2 cm at the tube window to ∼45 cm at a distance of 1 m from it, which agrees with the calculations performed.     

Studying the spectrum of neutrons emitted from the LSDS-100 using a multiwire proportional fission chamber

A fast multiwire proportional fission chamber capable of detecting ∼10⁶ fission fragments per second was produced. Heptane vapor at a pressure of 15 mbar was used as a working gas. The full width at the base of the pulse from a fission fragment was ≤0.2 μs. The spectrum of the neutron flux density on the spectrometer surface was measured by the neutron slowing-down time in the lead of the LSDS-100 at neutron energies ranging from 18 eV to 11.3 keV.     

A high-current picosecond electron accelerator with a low-impedance vacuum diode

A high-current picosecond (∼150 ps) electron accelerator with a beam energy of 50–100 keV is described. The use of a low-impedance vacuum diode at an amplitude of the arriving pulse of 300–400 kV made it possible to significantly increase the beam current (up to ∼15 kA) and the corresponding X-radiation intensity. One of the accelerator's applications in the X-ray therapy of malignant tumors. Some computational relations and results of measurements of the arriving and reflected voltage pulses near the diode are presented. The electron-accelerating voltage, beam current, vacuum-diode impedance, and other parameters are determined after the recovery procedure.     

Frictional Voltammetry with Copper

This paper presents an experimental study correlating frictional behavior with in situ voltammetry for a unidirectional sliding contact between a hemispherical tipped alumina probe and a flat rotating copper counterface (maximum Hertzian contact pressure of 68 MPa and sliding speed of 10 mm/s). The contact was immersed in an aqueous 0.1 M Na₂CO₃ solution (pH ∼11) where the copper counterface acted as the working electrode in a potentiostat controlled three-electrode cell; a coiled Pt wire was used as the counter electrode and a saturated calomel electrode (SCE) as the reference. Clear and reproducible trends were found between friction coefficient and published data suggesting the onset of particular redox reactions, graphically presented in a frictional voltammetry plot. At anodic potentials primarily associated with the formation of copper(I) oxide (Cu₂O) (V vs SCE ∼−0.25), the measured friction coefficient was in the range μ ∼0.4–0.5. At cathodic potentials primarily associated with the formation of CuO, Cu(OH)₂, and CuCO₃ (V vs SCE ∼−0.10), the friction coefficient transitions to the range μ ∼0.7–1.0. At sustained cathodic potentials associated with reduction of the native copper oxide, Cu₂O, (V vs SCE ∼−0.65), the friction coefficient is observed to fluctuate between μ ∼0.2 and 0.5, arguably a result of exposure of bare copper due to non-uniform reduction (fractional coverage) of Cu₂O.