Instruments and Experimental Techniques最新文献

A generator of powerful nanosecond pulses that contains a storage capacitor, a segment of a coaxial cable, and closing and opening semiconductor switches has been developed. With a storage-capacitor charging voltage of 12 kV, the generator allows switching quasi-rectangular voltage pulses with an amplitude of ~26 kV, a rise time of ~4 ns, and a fall time of ~6 ns into a 75 Ω load. The half-maximum pulse duration is ~45 ns, and the “jitter” relative to an external triggering signal is less than 2 ns. The possibility of increasing the generator output power and the duration of output-voltage pulses is shown.

The Baikal-GVD deep-sea Cherenkov detector, whose deployment in Lake Baikal has been ongoing since 2016, currently represents the largest neutrino telescope in the Northern Hemisphere. The principle of the telescope’s operation is based on the registration of Cherenkov radiation produced by the products of neutrino interaction in the aquatic environment using the spatial structure of photodetectors. Laser light sources specially designed for the Baikal project are used to calibrate and measure the characteristics of the telescope’s detecting system. The article describes the design and features of the functioning of calibration laser sources, presents the results of their operation as part of the telescope, and discusses issues of further development of the laser-calibration system.

A dilution cryostat is described, which is designed to carry out observations at dusk in the millimeter range on an optical telescope with a mirror with a diameter of 6 m, when observation in the optical range is still impossible. The cryostat, which cools the detector down to 0.1 K, is built according to the scheme of dissolving ³He in ⁴He with ³He circulation due to its condensation on a cold wall cooled by sorption pumping of pure liquid ³He from a separate volume. The working conditions are provided by the contact with the stabilizing unit, which accumulates 0.6 L of liquid ⁴He during active operation of a Gifford–McMahon refrigerator within the time between measurement cycles. During measurements, the refrigerator turns off, which completely eliminates vibrations that interfere with measurements.

Over the last two decades, the superconducting qubits have become a promising and rapidly growing area of research. However, there are specific challenges when working with such a delicate system. One of them is the qubit state readout. Since a very small signal (of the order of 1 photon) is used for the readout, its detection is challenging and it requires low-noise cryogenic amplifiers working in the 3–12 GHz frequency range. Josephson parametric amplifiers (JPAs) are one of the most studied and developed candidates. Currently, several JPA designs offer low noise performance and instantaneous bandwidth from tens of MHz to several GHz; they are also becoming an integral part of circuit quantum electrodynamics (cQED) setups. In the current work, results are presented of the measurements of a JPA made of a coplanar waveguide with an array of three SQUIDs. Nondegenerate amplification and an amplifier added noise being close to the quantum limit are demonstrated.

The theoretical and experimental characteristics of depth dose distributions of protons in the Bragg peak region are investigated. Results of the Monte Carlo calculations in the TOPAS MC software package and experimental data obtained from film detectors and ionization chambers at the high-current proton linear accelerator of the Institute for Nuclear Research are used. The interrelationship between the results and the applicability of these detectors for measuring the absorbed dose are considered. The calculated dose distributions are in good agreement with the dose distributions measured using the ionization chambers for the pristine and spread-out Bragg peaks. Possible interrelationship between the linear energy transfer and the accuracy of dose measurements with the film detectors is shown. The discrepancy between the readings of the film detectors in the Bragg peak region, on the one hand, and the results of calculations and measurements with the ionization chambers, on the other hand, may be important for irradiation of biological samples, in particular, in the FLASH therapy modes.

The results of a study of a new Cherenkov monitor of proton beams with a high pulsed current are presented. Good measurement agreement was obtained for the monitor, Gafchromic detector, and induction sensor for 160 MeV proton beam and pulsed average current 1 mA. Bench measurements of the coordinates of the position of the light flux simulating the light image of a proton beam in the radiator of a two-dimensional monitor were carried out. A comparative analysis of algorithms for reconstructing the coordinates of the light beam position with the results of monitor simulation is presented.

A high-power source of ultrawideband radiation with elliptical polarization based on a 64-element array of spiral antennas was developed. The array was excited by a bipolar voltage pulse with an amplitude of up to 240 kV and a duration of 1 ns at a repetition rate of 100 Hz. Radiation pulses with an ellipticity coefficient of 0.64 and a peak field strength of 250 kV/m at a distance of 10 m were obtained.

A system is described for introducing microwave power into the vacuum chamber of a tokamak for preionization of the gaseous medium located there in order to facilitate subsequent discharge in it. Three main problems arising in this case are considered and a way to solve them is proposed. The calculation model of the electromagnetic structure includes a mode converter, a dielectric transformer, and a galvanic isolation unit. All geometric parameters of the device components were optimized. The described microwave power input device is made of nonmagnetic stainless steel and is currently used at the MEPhI training and demonstration tokamak.

Space precision payloads and microgravity science experiments are easily affected by low frequency micro-vibrations. The measurement and control of low frequency micro-vibrations are still critically needed. To overcome the measurement and control problem of low frequency micro-vibrations, a low frequency dynamic force sensor (LFDFS) and an active vibration control method are developed. Based on the LFDFS, an active vibration isolation platform is built to validate the low frequency measurement performance of the sensor. The dynamic modeling and simulation studies of the vibration isolation platform are further implemented. A composite control method employing both feedforward and feedback is proposed. Finally, the experimental results verify the performance of the developed LFDFS and the active vibration isolation effectiveness of the proposed composite controller.

The cryogenic system of the RED-100 two-phase emission detector has been modified to enable operation with liquid argon as a working medium with the aim of searching for the effect of coherent elastic scattering of reactor electron antineutrinos by argon nuclei.