S. V. Bobashev

A study of vacuum-ultraviolet stability of silicon photodiodes

Silicon photodiodes have been tested for resistance to vacuum-ultraviolet radiation at 121.6 nm. The responsivities of the p-n and n-p photodiodes under study were found to degrade by tens of percent at a VUV radiation dose on the order of tens of mJ/cm2. The effect of reversible photocurrent relaxation has been observed in detectors based on n-p structures.

Magnetohydrodynamic control of a supersonic flow about a body

The structure and principle of operation of an electromagnetic facility capable of controlling a supersonic flow about a body of revolution are described, by means of which gas-discharge plasma formed between electrodes flush-mounted on the body is driven over its surface by a magnetic field. It is shown that the frequency of rotation of the gas-discharge plasma strongly depends on the direction of electric current flowing through the facility, as well as on the pressure of ambient gas. Experimental results demonstrating the effective magnetohydrodynamic control over the structure of supersonic nitrogen flow about the body of revolution at a Mach number of 4 are presented.

Peculiarities of interaction of a shock wave with gas discharge plasma

Using a double electrical probe, distribution of charged particles behind the front of a shock wave in gas discharge plasma in the presence of the electric field and in decaying plasma without the electric field was studied. A significant difference between the distributions of the charged particles in these two cases was revealed.

Using anisotropic heat flux sensors in aerodynamic experiments

We present the results of comparative measurements of the heat flux to a flat plate in a supersonic flow at a Mach number of M = 6, which were performed using the two following anisotropic heat sensors with different thicknesses of sensor elements: (i) Atomic Layer Thermo Pile (ALTP, Fortech GmbH, Germany) with a thickness of ∼0.5 × 10−6 m and (ii) gradient heat flux sensor (GHFS, St. Petersburg State Polytechnic University, Russia) with a thickness of ∼2 × 10−4 m. The ALTP sensor can be used for directly measuring heat fluxes in processes with a characteristic time above 10−6 s. A method for mathematically processing the GHFS response signal is proposed that allows heat flux oscillations to be revealed in gasdynamic process with a characteristic time on the order of 10−4 s.

Experimental investigation of magnetohydrodynamic action on a heat flux toward the surface of a model

Experimental data for magnetohydrodynamic (MHD) action on a supersonic nitrogen flow about an axisymmetric model are presented. The experiments were carried out in the Big Shock Tube (Ioffe Physical-Technical Institute), at the end of which a test section equipped with a supersonic nozzle was mounted. A test conic model coupled with a cylinder is attached to the output cross section of the nozzle. A magnetic field is produced by a solenoid placed on the cylindrical part of the model through which a pulsed current due to an external voltage source discharging passes. Electrodes on the conic part of the model initiate a gas discharge, which rotates about the axis of the model in the solenoidal magnetic field. The influence of the magnetic field on the gasdynamic pattern of the flow near the model and on the heat flux toward its surface is investigated. Schlieren patterns of the flow about the model, photographic scans of the discharge glow, and heat flux measurements are taken. It is found that the magnetic field has an effect on the gasdynamic pattern of the flow near the model and on the heat flux toward its surface. The dependence of MHD effects on the external voltage polarity is also revealed.

Magnetic field control of a supersonic nitrogen flow

Magnetohydrodynamic impact on a cold supersonic nitrogen flow with external magnetic field was realized in an experimental complex based on the Big Shock Tube at the Ioffe Physicotechnical Institute. A pulsed supersonic flow with a Mach number of M=4 and steady phase duration of about 1.5 ms was created by expansion of the shock-heated nitrogen flow from a supersonic nozzle. The gas was ionized by pulsed discharge between two electrodes mounted on the nozzle wall so that an electric current of up to ∼500 A passed in the direction perpendicular to the gas flow at the dielectric wall. External magnetic field ∼0.3 T was perpendicular to the gas flow and the current direction. It is established that the magnetic field significantly modifies the shock wave structure in the flow.

A new method for determining the efficiency of laser radiation conversion into 13.5 ± 0.3 nm radiation in laser-plasma extreme ultraviolet sources

We have studied extreme ultraviolet (EUV) emission from a laser-plasma source employing a supersonic xenon jet as the target. The output EUV energy has been determined as a function of the laser pulse energy for the supersonic xenon jet in comparison to the solid metal (Cu, Mo, Ta) targets. Based on these results, a new method for determining the efficiency of laser radiation conversion into EUV radiation is proposed, which ensures unambiguous characterization of the properties of various targets. Ways to optimize the xenon jet source are discussed.

Thermal measurements at the body surface in a supersonic nitrogen flow

Measurements of the heat flux toward the surface of a body of revolution in a supersonic nitrogen flow with Mach number 4 were carried out. Inside the body, an electromagnetic facility is mounted which generates a gas-discharge plasma between electrodes flush-mounted at the body surface. The plasma rotates around the body surface and significantly influences the supersonic flow. During operation of the electromagnetic facility, the heat flux toward the body surface increases and depends on the direction of the electric current flowing through the plasma. The heat flux was measured by fast-response gradient heat flux sensors based on anisotropic bismuth crystals.

Photoresponse of a Silicon Multipixel Photon Counter in the Vacuum Ultraviolet Range

Photoresponse of a silicon multipixel photon counter (MPPC) operating in the Geiger breakdown regime has been studied at wavelengths λ = 115, 121, 128, 160, and 175 nm. It is established that radiation intensity at these wavelengths can be measured by MPPC at room temperature in the photon-count mode with efficiency on a level of 2%.

Algorithm for determining the aerodynamic characteristics of a freely flying object from discrete data of ballistic experiment. Part I

An algorithm for solving the inverse problem of dynamics is described. It is intended for processing trajectory data for a freely flying object that are acquired in ground-based (laboratory) simulation on a ballistic range with the aim of determining the aerodynamic characteristics of the object.