Instruments and Experimental Techniques最新文献

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.

A method for measuring and installing four switchable polarization planes in a microwave radiometer using a Faraday cell is considered. The calibrated radiometer is designed to record weak polarization effects, for example, azimuthal anisotropy that occurs during the formation of the intrinsic radiation of a rough sea surface. To solve such problems, it is necessary to absolutely link all polarization modes of the radiometer to the horizon level with an accuracy of no worse than 0.5°. In the proposed measurement scheme, radiation from a gas-discharge tube with an output antenna on horizontal polarization was used as a broadband microwave source, which was additionally reflected from the water surface at the Brewster angle. This provided additional suppression of the vertical component of the radiation by –12 dB and the formation of strictly horizontal polarization of the reflected wave since the free surface of the water in the bath is horizontal with an accuracy of greater than 0.05°. Traditional sources of polarized radiation do not provide horizontal orientation of the emitted signal with the specified accuracy. In the proposed method, the installation errors of the vertical, horizontal, and crossed at the angles of ±45° planes of polarization were no more than ±0.3°. The measurement of the installation angles of the polarization plane was carried out by with an accuracy of 0.1° rotating the radiometer around the axis of the receiving antenna and approximating the data by the Malus law. The adjustment of the angles was controlled by currents through the Faraday cell.

A relatively simple circuit of a selective meter of constant and variable components of the total current of a photomultiplier when recording magnetic circular dichroism spectra in reflected light using the method of light-wave phase modulation with the help of a photoelastic modulator is presented. The circuit implements a method for measuring the photomultiplier anode current using a load resistance R_L and a buffer preamplifier. The variable current component is extracted via compensation of the constant component of the total signal. The experimental techniques are described that make it possible to determine the optimal R_L value for which the influence of the input shunt capacitance is minimal in the frequency band of ~100 kHz. The main source and level of the parasitic photocurrent not associated with the incident monochromatic radiation are determined. The meter testing showed high efficiency of its use in magnetic circular dichroism spectroscopy. An algorithm for spectrum recording is proposed taking the change in the circular dichroism effect polarity into account. The performance and efficiency of the developed meter are illustrated by an example of measuring the magnetic circular dichroism spectrum of a GaMnAs film.

A stepper electric motor has been designed to rotate a sample in an experimental cell inside a cryostat with ³He pumping. The device based on a rotor with crossed electrical windings, operates in an external magnetic field generated by a superconducting magnet. A prototype of the motor was mounted on a microwave spectrometer with a rectangular resonator. Test angular dependence of the magnetic resonance spectrum was obtained in a well-studied weak ferromagnet ({text{MnC}}{{{text{O}}}_{3}}) at temperatures 0.5–7.5 K in the range of angles ±100° from the initial position. Overheating of the cell and cryostat was studied and the heat release during operation of the mechanism was estimated.

Hundreds of 650 MHz superconducting radio-frequency (SRF) cavities with high intrinsic quality factor (Q₀) and accelerating gradient (E_acc) will be adopted for Circular Electron Positron Collider (CEPC). The values of Q₀ and E_acc are obtained during vertical test at 2.0 K. Hence, high accuracy of vertical test is essential for evaluating the performance of SRF cavity. The 650 MHz SRF cavities achieved very high Q₀ (6 × 10¹⁰) and E_acc (40 MV/m) during the vertical test. In our study, the error analysis of vertical test was conducted in the scalar case, in order to achieve high accuracy. The uncertainties of vertical test were obtained through calculation, which was approximately 3% for E_acc and less than 5% for Q₀. This result was reasonable and acceptable.

Ballistic design work has been carried out to assess the appearance and dimensions of the double-barrel launcher with an accelerating-channel length of up to 1 m. Based on the ballistic design, the development, design study, and manufacture of the double-barrel launcher have been performed. An ignition system has been developed, with which it is possible to throw two supercavitating strikers into an air or water environment simultaneously and with a programmable delay. Test experiments on throwing two supercavitating strikers into air and water have been conducted under the conditions of a hydroballistic stand.