卷 62, 编号 2 (2019)

The characteristics of the quasi-monochromatic calibration beam of secondary electrons at the Pakhra accelerator (Lebedev Physical Institute) on the basis of the SP-57 magnet are presented. The energy resolution of the beam with a copper converter 0.1–5.0 mm thick and an interpolar magnet gap of 6 cm is δ = 10.0–4.5% in accordance with the energy in the electron-beam energy range E = 98–294 MeV.

The control system for the detectors of the SPASCHARM experimental setup that is being developed at the U-70 accelerator complex (Protvino) is described. The general design concept of the control system and an example of application of the EPICS software are considered. The electronic modules of the control system that have been put in operation as of the present are described.

The results of pilot studies of silicon shock-ionized dynistors (SIDs), which belong to the class of thyristor-type semiconductor devices that are able to be switched to a highly conducting state within a time shorter than 1 ns upon application of a short overvoltage pulse that initiates an impact-ionization process, are presented. The excellent characteristics of SIDs in the mode of switching high-power current pulses of nanosecond duration are demonstrated. Experiments are described that indirectly confirm the ability to initiate the process of subnanosecond switching of an SID by holes that are injected from a p⁺ emitter.

A series of high-voltage (20–50 kV) DC power sources (1–10 kW) was developed based on the circuit of high-frequency conversion with wide-range regulation of the output voltage via conversion frequency tuning. A sinusoidal current shape provides switching of power transistors at the zero current and the short-circuit protection in a load. The source provides an output voltage with small ripples and, when powered from a three-phase network, it does not require a smoothing mains filter.

A multichannel diagnostic unit for charge-exchange atoms was created at the Gas Dynamic Trap to study fast ions with energies in the thermonuclear range, which are produced during high-power atomic injection. Two detection systems based on the pinhole camera principle were developed to observe the radial distribution of the emission of charge-exchange atoms. AXUV16ELG semiconductor photodiodes, as well as experimental diodes developed by the Rzhanov Institute of Semiconductor Physics that are capable of operating in the avalanche amplification mode, are used as sensitive the elements. Using this diagnostic unit, it is possible to study the dynamics of accumulation and confinement of fast particles and, in particular, to investigate the processes associated with the magnetohydrodynamic activity of hot ion plasma under conditions of a high relative pressure.

Abstrac

t—The results of studying the influence of radiation defects on the error of measuring the total energy of a high-intensity pulsed ion beam and its cross-sectional distribution using the thermal-imaging diagnostics (TID) are presented. The investigations were carried out at the TEMP-6 accelerator (200–250 kV, 120 ns) during operation of an ion diode in the mode of self-magnetic insulation of electrons. The ion beam consisted of С⁺ carbon ions (85%) and protons; the energy density at the focus was 1–5 J/cm². It was found that when targets of different metals (titanium, stainless steel, and copper) are used, the readings of the TID differed by 40–60% for the energy-density instability in a pulse train (for a single target) of at most 10%. The causes of errors in the energy-density measurements were analyzed. It is shown that when a metal target is irradiated with a powerful ion beam, a significant number of radiation defects are formed in it. The ion-energy losses on their formation are proportional to the initial thermal energy in the target after its irradiation with the ion beam and have values of 22% in stainless steel, 30% in copper, and 70% in titanium targets. When the ion-energy loss on the formation of radiation defects is taken into account, the error of the TID technique does not exceed 15% when using targets of different metals.

The possibility of the simultaneous operation of avalanche photodiodes in the photon-counting and current modes is shown. The double-mode operation is provided at a constant supply voltage of an avalanche photodiode that exceeds the breakdown voltage of its p–n junction. The probability of the formation of microplasma pulses as a function of the intensity of optical radiation and the supply voltage of the avalanche photodiode is estimated for the considered operating mode.

An autocorrelator based on the noncollinear generation of the second harmonic in a crystal for duration measurements of single sub-10-fs laser pulses was developed. The measured pulse duration of a broadband laser system was 6.2 fs.

A method is presented for measuring the energy density of X-ray pulses with a duration of approximately 200 ns from a source with an energy of 2–3 J in its discharge circuit. A bismuth germanate (BGO) scintillator crystal is used for measurements. The absolute calibration of the energy scale has been carried out by measuring the amplitude spectrum of cosmic muons. The energy flux of an X-ray pulse, measured at a distance of 1 m from the anode of the source, is 20 GeV/cm².

In this work, two contact resonant ultrasound spectroscopy arrangements, one measuring in the frequency- and the other in the time-domain, are compared. Both set-ups use the same shear wave piezoelectric transducers for excitation and detection. Frequency-scan and acquisition with a lock-in amplifier is used for the frequency-domain measurement. As for the time-domain measurement, narrow square-pulse excitation and oscilloscope signal acquisition are employed. Output-to-input ultrasonic amplitude spectra are obtained with both arrangements for two samples of brass and polymethyl methacrylate. Fits of the more distinctive peaks of the spectra to Lorentzians yields limits of agreement between time- and frequency-domain measurements of the order of 5 × 10^–2 kHz for most of the peaks considered. For brass, the full widths at half maximum of the frequency-domain peaks are of the order of 69 to 85% smaller than those of the corresponding time-domain peaks. For polymethyl methacrylate the differences in full widths at half maximum between corresponding frequency- and time-domain peaks fall into the range of error.

The design, principle of operation, and results of tests of a Fourier-transform spectrometer, which is designed for studying the composition of the Martian atmosphere by the transmission technique, are described. A standard specimen of the instrument must operate on the landing platform after its delivery to Mars. The spectral range of the manufactured specimen is 0.5–4 μm, the spectral resolution is 0.04 cm^–1, the aperture is 25 mm, and the mass is 1.1 kg.

A method for measuring large displacements >800 mm with a precision of 0.0094% and an accuracy of 0.0125%, realizing the principle of measurement with walking pattern and utilizing two analog high-precision small displacement sensors as the measuring unit is presented. A self-tuning fuzzy PID controller with high adaptability is used to make two identical measuring subsystems work coordinately for reaching a large displacement measurement. A series of tests are conducted to verify the effectiveness of the method. The results show that this method has a good performance. The influence of the mechanical deformation on measuring precision is discussed, and the functional relationship between mechanical structural deformation and measuring error is found in the experiment. A feasible compensation scheme is built to eliminate the error caused by mechanical deformation.

The paper presents a detailed description of laboratory techniques and equipment used for measurements of a velocity field under regular standing surface waves in vicinity of a rigid vertical wall. The waves are generated in a closed flume by a monochromatic motion of a piston-type wavemaker and are reflected at a wall installed in a wave flume. A superposition of incident and reflected waves forms a standing wave. Particle image velocimetry technique is employed to measure evolution of a velocity field of wave-induced flow. The available data are used to calculate water particle trajectories of a standing wave system. Thus, a complete information on standing wave kinematics is obtained. The experimental results confirm that mass transport in Eulerian and Lagrangian sense cancels out in case of two progressive waves of lower steepness forming a standing wave. The experimental data may serve as a reference basis for theoretical models of waves interacting with vertical barriers. Moreover, important conclusions regarding the design of improved experimental setup leading to a better description of spatiotemporal velocity distribution under wavy surface are formulated.

An apparatus for conducting chemical reactions with microwave heating of reagents was developed. It consists of a microwave oscillator based on a domestic magnetron with deep regulation of the microwave-power level and a device for microwave heating, which is a microwave reactor that contains a high-Q cavity resonator and a chemical reactor built into it.

We have designed and developed an experimental setup to measure the Seebeck coefficient of a variety of samples at cryogenic temperatures and under magnetic fields up to 7 T employing the physical property measurement system (PPMS). The measurement technique uses a low frequency ac thermal gradient generated by two thin film heaters in thermal contact with the sample. Heaters and temperature sensors are all fitted on a standard PPMS sample puck. The validity of this method is tested by measuring the thermoelectric power of several superconductors and thermoelectric samples. We have used this technique to measure the thermoelectric power of various topological insulator single crystals (Pb_0.8Sn_0.2Te, Bi₂Te₃, Bi₂Se_2.1Te_0.9, and Sb₂Te₃). The developed hardware and software control is suitable for studying the thermoelectric power of small samples (length 2 mm) in a commercial cryomagnetic system (PPMS) and it allows for studying superconductor, semiconductor, thermoelectric, or topological insulator material in wide temperature (2–300 K) and magnetic field (0–7 T) ranges.