Vol 60, No 3 (2017)

A new specialized MPD Test Beam setup was mounted at the extracted beam of the Nuclotron at the Joint Institute for Nuclear Research to carry out methodical research and test detectors produced for the MPD experiment at the NICA accelerating facility. The setup is described in detail. The results of the testing of fast detectors for the MPD time-of-flight system are presented as an example of the operation of the setup.

Silicon photomultipliers (SiPMs) are used in detectors of the GlueX experiment devoted to studying the nature of confinement. These detectors are operable at counting rates as high as 2 MHz with a time resolution (FWHM) of approximately 0.3 ns and a number of excited pixels of up to 10⁴. For SiPMs that operate under these conditions, the measured dependences of the recovery time and the time resolution are presented as functions of the number of excited pixels and the excitation frequency. Using a picosecond laser, the time resolution has been measured for an array of 4 × 4 SiPMs, which was specially developed for the experiment.

Comparative results of recording and processing of particle tracks in track detectors by laser radiation with varying degrees of coherence are presented. The necessity to optimize the transformation parameter of the laser field coherence for each particular experimental task is substantiated.

A new control system for capacitive energy storage with a rated energy content as high as 16 MJ is described. Capacitive energy storage has been used since 1987 to supply power for the pulsed magnetic system of the GOL-3 multiple-mirror trap. It has an operating voltage of 6 kV and consists of 6000 IK-6-150 capacitors that are located in six remote rooms together with the necessary infrastructure. The system for control and data acquisition was built using Arduino microcontroller boards operating as a distributed network of remote servers. The client part of the control system uses a personal computer with a standard configuration; communication with remote servers is effected by the TCP/IP protocol. The control system was put into regular operation at devices of the GOL-3 facility in the early 2016.

A method for experimental evaluation of the magnetic-field attenuation coefficients under a pulsed action is considered. A technique for the preliminary processing of measurement results for low useful signal-to-noise ratios is considered taking the features of the operation of digital oscilloscopes into account. The analysis of the spectral composition of measured signals and a method for their approximation in the time domain, which allows elimination of the influence of measuring-sensor noise and digital-oscilloscope rounding errors, are presented. The results of estimating the frequency dependence of the magnetic-field attenuation coefficients for a copper shield in comparison with the results of a theoretical calculation are presented. The considered method allows simultaneous determination of the coefficients of the magnetic-field attenuation by the shield in a wide frequency range.

A multistage generator of high-voltage pulses with a scroll geometry of spark switches, which is produced according to the Marx scheme, is presented. The device is designed for a small pulsed neutron source and makes it possible to obtain accelerating-voltage pulses with amplitudes of up to 450 kV at a stored energy of up to 50 J and a load current of up to 1.5 kA.

A technique for investigating the spatial structure of X-ray and ion-emission sources from micropinch- discharge plasma (MDP) is described and the investigation results are presented. A spectrometric system has been developed that allows measurements of the spectral characteristics of the ion emission for ions of different degrees of ionization from different MDP regions in a device of the low-inductance vacuum-spark type.

An installation to study a pulsed gas discharge in a diode with a single metal tip by laser probing has been devised. The installation represents a generator comprised of cable sections connected to a five-channel laser-triggered switch. The synchronization of the probing laser beam with the voltage pulse is not worse than ~1 ns. The moment of probing is determined by the optical delay and can be varied independently within the range of 10–20 ns by changing the charging voltage of the cables. The pressure in the discharge chamber can be varied from 10^–5 Torr to atmospheric pressure. Copper or molybdenum wires with a diameter of 10 μm or greater were used as cathode pins. Three independent optical record channels with time delays of 2 and 13 ns relative to the first channel allow one to simultaneously obtain interferograms and shadow and schlieren images of the discharge gap with spatial and time resolutions of 20 μm and 70 ps, respectively, with the exposure time of each frame being equal to a laser pulse duration of 70 ps. Using the devised installation, qualitative and quantitative data on the prebreakdown processes that occur in a tip-type diode have been obtained within a wide range of pressures.

An energy-dispersion scheme for determining the conсentrations of impurities of heavy elements from the absorption spectra in the regions of X-ray photoabsorption jumps is described. A semiconductor X-ray spectrometer and a pyrolytic graphite monochromator were used to record data in a spectral band of width up to 1 keV. The initial shape of the absorption spectrum in the approximation of an isolated atom was reconstructed by means of a numerical solution of the convolution equation. The scheme provides a sharp increase in the data acquisition and measurement sensitivity. The results of measurements of the Bi and Pb contents in samples with organic matrices and determination of the thicknesses of thin Mo films on diamond substrates are presented.

An analysis of various optical schemes for the development of a laser SF₆ gas analyzer based on a CO₂ laser operating in free-running mode and a resonant photo-acoustic detector (PAD) is presented. The use of a sealed gas-filled cell to normalize PAD signals on the absorbed power in the cell is suggested. Compensation for the influence of the tuning of the CO₂ laser wavelength near 10.6 μm on measured SF₆ concentration is possible. The results of experimental studies of a laser photo-acoustic SF₆ gas analyzer at various concentrations, including in the air flow, are presented. It is shown experimentally that the relative measurement error of the SF₆ concentration due to the instability of the laser radiation wavelength does not exceed 5% in the range from ~80 ppb to 40 ppm. The limit of the sensitivity of the developed gas analyzer was ~1 ppb SF₆.

The use of visualization techniques in the research on thermohydraulic processes using large-scale models of nuclear power plants is discussed. In particular, the original particle-image velocimetry (PIV) measurement system at the TISEI test bench was presented, which is a model of a proposed fast-neutron reactor. Illumination and video-filming systems with the simultaneous use of several lasers and camcorders, as well as image-processing algorithms that make it possible to carry out field measurements with high precision in a complex configuration of the reactor model, reflections and distortions of the laser knife section, and shadowing by obstacles are described. The developed methodology of conversion of the image coordinates and velocity field into the reference system of the reactor model using a virtual 3D simulation made it possible to significantly simplify the experiments.

Experiments to determine the maximum size of through pores in MFAS-type membranes (Vladipor Company) were carried out in two ways: by the “bubble-point” method according to GOST (State Standard) 50516-93 and the “crystallization-onset” method. The experimental values of the pressure difference upon the appearance of bubbles in a liquid and the temperature of the crystallization onset were obtained for membranes of different brands. It was shown that the membrane thickness influences these parameters. Repeated measurements of the maximum size of through pores were performed and showed good reproducibility of the experimental data.

The simplicity and accuracy in determining the exact concentration of a particular substance in a solution, is one of the major issues in industrial chemistry. In this paper, we introduce a new technique based on Compton scattering of gamma photons and artificial intelligence to determine the concentration of a solute in a solution. We used a ¹³⁷Cs gamma ray source with few millicurie activity and a NaI(Tl) scintillator detector to determine the acid sulfuric molarity. We also applied Adaptive Neuro-Fuzzy Inference System (ANFIS) and Artificial Neural Network (ANN) as artificial intelligence techniques to estimate the molarity of the samples. Monte Carlo simulations also support the present experimental results. The results of the proposed methods are in excellent agreement with the measured molarities.

A photodetector device that is intended for absorption measurements at a level of 10^–2–10^–3 under the conditions of large intensity fluctuations of probing radiation, nonstationary broadband illumination of the photodetector, and in the presence of electromagnetic interference is described. Using a differential measurement circuit, an absorption signal is formed in the analog manner and amplified to a level of ~1 V directly near the photodetector. During periodic wavelength scanning, the influence of the broadband illumination and vibrations is compensated at the beginning of each scan. This compensation is preserved during a current scan and renewed in each subsequent scan due to the use of sample-and-hold amplifiers. The device can be used in the diagnostics of turbulent gas flows and flames.