Instruments and Experimental Techniques最新文献

A design of a nanosecond pulse generator is presented. The pulses are generated by the avalanche breakdown of the transistor, which also participates in the generation of the voltage required for the avalanche breakdown of the collector junction. As a result, the circuit is compact and operable from supply voltage 1.1 V. The circuit is very simple, does not require adjustment, and the parts used are available. The amplitude of the generated pulses is approximately equal to 40 V on a load of 50 Ω.

Traditionally, the calibration of the probe work function for Kelvin scanning microscopy is carried out using highly oriented pyrolytic graphite. In this paper, it is proposed to supplement it with calibration using indium- and fluorine-doped tin oxide (ITO and FTO). The study is performed using platinum- and gold-coated probes. Based on the calibration results, the positions of the Fermi levels of lead sulfide nanocrystals with ligand shells of 1,2-ethanedithiol and tetrabutylammonium iodide are determined. It is shown that the selected oxides are characterized by a stable working function, an additional calibration using these oxides helps to more reliably determine the absolute position of the probe work function, and gold probes provide a more stable result. The selected oxides can be used as an addition to the calibration using pyrolytic graphite, as well as independently.

The paper presents measurements of the thermal conductivity and thermal diffusivity coefficients of graphene oxide (GO) thin films in three mutually perpendicular directions in the temperature ranges from 203 to 373 K. The process and features of measuring GO thin films at temperatures near GO reduction temperatures (approximately 393 K) are described in detail. Using the laser flash method (LFA), the method of differential scanning calorimetry (DSC), and hydrostatic weighing, experimental dependences of specific heat capacity, density, thermal conductivity, and thermal diffusivity coefficients on the temperature of thin GO films were obtained. As a result of the work, the specific heat capacity, thermal diffusivity, and thermal conductivity of thin GO films were measured as functions of temperature, and it was also found that the use of the flash method for measuring thermal diffusivity in the temperature range from 273 to 373 K makes it possible to consider anisotropic materials as orthotropic.

Boron neutron capture therapy, a promising method for treating malignant tumors, requires accelerator sources of neutrons in the epithermal energy range. One of the popular charged particle accelerators is a tandem electrostatic accelerator of an original design, later called the vacuum insulated tandem accelerator VITA. The paper presents the results of measuring the phase portrait of an ion beam obtained at an experimental facility at Budker Institute of Nuclear Physics and at oncology clinic facilities that feature preacceleration. The advantages and disadvantages of using preacceleration are shown. Proposals are made to improve the vacuum insulated tandem accelerator, which require experimental verification.

A laboratory experimental setup based on a three-mirror ring resonator (traveling-wave interferometer) designed for the visual demonstration and studying the spectral features of helium–neon laser radiation in several lasing modes is presented. In particular, this installation makes it possible to measure the parameters of the interferometer mirrors, including the transmission and reflection coefficients. The installation can be used in laboratory workshops for students who are starting to study the physical foundations and operating principles of gas lasers. The installation contains elements of single-mode fiber optics.

The paper describes an original setup for studying the contribution of capillary waves in the range of wave numbers k = 100–1200 rad/m to the microwave radiation of the surface. A feature of the technical solution is the generation of an almost monochromatic capillary grid of waves on the surface of a flat vessel, which allows for a “pure” study of critical phenomena occurring in the microwave radiation of the surface at certain observation angles. The generation of capillary waves of a given frequency and amplitude was carried out by a thin bar on the surface and its oscillations were set by the author’s device located under the water surface. The shape of the resulting wave was recorded with the accuracy of 0.03 mm by an original method based on reflections from the surface. The vertical observation angle varied from 8° to 70° and the azimuthal rotation angles of the capillary grating changed by 360°. The microwave radiometer made it possible to measure variations in brightness temperature in four polarizations with the sensitivity of 0.1 K and with the accumulation time of 1 s. It was found that capillary waves with the amplitude of only 0.15–0.20 mm cause a resonant increase in the radiation intensity, reaching 5–6.5 K. Both the amplitude and the position of the resonant peak, which shifted to smaller elevation angles as the capillary wave length tended to the radiation wavelength, are consistent with the theory.

A two-channel ion cyclotron resonance heating system has been produced at the L-2M stellarator for introducing RF radiation with a power of 2 kW into the plasma. This system has been used for preliminary plasma ionization preceding the creation of main plasma in the ohmic heating regime in the L-2M stellarator. It has been demonstrated in the preionization experiments that the loop voltage is reduced by approximately 15% immediately before the breakdown of the working gas. In addition, the generation of runaway electrons is efficiently suppressed by RF radiation in the initial stage of discharge formation. The evidence of this suppression is a tenfold decrease in the intensity of hard X-ray radiation.

Imaging Plates (IP) are widely used in laser-plasma and radiographic experiments for detection of electrons, ions, and X-rays. The use of IP in plasma diagnostics allows for obtaining quantitative information about plasma parameters. This paper presents the results of calibration of FujiFilm Imaging Plates BAS-MS and BAS-TR for X-rays in the range up to 10 MeV. Calibration was performed using the Ge-68 radioactive positron source and the Durr Dental VistaScan Mini View laser medical scanner.

The article is devoted to the modernization of the micromarking device based on a commercially available CNC2418 engraving machine. The purpose of the upgrade is to reduce the size of individual marking imprints. It is proposed to increase the accuracy of the movement of the tungsten probe in the vertical direction and to control its contact with the surface. A mechanical reduction gear is described that reduces the drives step value along the vertical axis from 10 to 1.5 μm and consists of a cantilevered piezoelectric plate and a cylindrical spring connected to a step drive. Three methods for monitoring the contact of the marker probe with the sample surface, based on measuring the electromechanical parameters of the piezoelectric plate and using a widely available oscilloscope or a multimeter, are described. The application of the proposed solutions allowed to reduce the area of individual marking imprints by 1.9 times.

The pulsed magnetic field setup created at Ioffe Physics and Technology Institute allows measuring transport phenomena (Hall effect, magnetoresistance) of materials in a pulsed magnetic field with multiple pulses of amplitude up to 35 T and pulse duration of 10 ms. The rationale for the optimal choice of the installation structure, circuit design, and processing algorithms is provided. Ease of operation with low operating costs makes the unit a good choice for a scientific laboratory.