Search

The phenomena occurring in dielectrics (Al2O3 and SiO2) in the field of high-power soft X-ray radiation are investigated. Experimental studies are carried out at the Angara-5-1 facility, which allows a pulsed radiation power density of the source up to 5 MW/cm2 at the location of the examined samples. It is revealed that charge carriers are generated in the surface layer of the irradiated dielectric, which causes current generation in a circuit including the dielectric. A necessary condition for current generation is the presence of "hot" electrons, which provide surface conductivity. A mathematical model is proposed to describe the process of current generation in dielectrics during exposure to high-power pulsed X-ray radiation. The model is based on the joint solution of the kinetic equations for X-ray photons, photoelectrons, conduction electrons and holes in the valence band and self-consistent Maxwell's equations. In Maxwell's equations, instead of the external current of secondary charge carriers, the radiation conduction current is used. [ABSTRACT FROM AUTHOR]

A method for triggering a laser synchro-signal diode in a single-pass quantum cryptographic system is proposed. The method allows reducing the level of stray influence in an optical fiber from scattered laser radiation by 2 orders of magnitude and increasing the length of a single-fiber communication line when generating a secret key to 95 km. [ABSTRACT FROM AUTHOR]

The high sensitivity of traditional diagnostic methods hinders their application in inertial confinement fusion with the pulsed radiation power of target plasma being as high as 1013–1014 W. Different methods of attenuating the incident radiation flux either alter its characteristics or are too complicated. The results of tests of a new detector, where quartz glass is used as a sensing element, at the Angara-5-1 facility are presented. It is demonstrated experimentally that the detector sensitivity is ~2 V/(MW cm2) and the time resolution is ~1 ns. The mechanism of formation of the response signal, where the temperature of electrons produced under irradiation plays a significant part, is discussed. [ABSTRACT FROM AUTHOR]

A module for recording single-photon pulses is described. It is able to reliably operate in the mode of single-photon counting at a wavelength of 1550 nm (the minimum attenuation in quartz fibers). For this purpose, unique avalanche photodetectors (APDs) based on InGaAs/InP heterostructures with the three-stage cooling to temperatures of -50°C via Peltier elements are used during reception. Test measurements of the level of noise counts, including both dark pulses and afterpulses, have been performed using the developed testing system. The dependences of the recorded noise counts on the duration of gate pulses have been obtained. The nonlinear character of these dependences is evidence of the difference in the contributions of the afterpulsing effect and the dark pulses of the APDs to the noise counts. At short durations of the gate pulses, the major contribution to the noise counts is made by dark pulses of the APDs. [ABSTRACT FROM AUTHOR]

A quantum random number generator is experimentally realized. The initial randomness source is a sequence of photocounts from quasi-single-photon radiation detected with a SiPM (Silicon Photo Multiplier) silicon avalanche detector array. The use of a SiPM provides a reliable control of the quantum nature of the Poisson photocount statistics. A special algorithm with nonexponential complexity allows one to extract from the Poisson process all the randomness contained in it, namely, a random uniform sequence of 0 and 1. [ABSTRACT FROM AUTHOR]

Results from experimental studies of implosion of nested wire and fiber arrays at currents of up to 4 MA at the Angara-5-1 facility are presented. Depending on the ratio between the radii of the inner and outer arrays, different modes of the plasma flow in the space between the inner and outer arrays were implemented: the sub-Alfvénic (Vr < VA) and super-Alfvénic (Vr > VA) modes and a mode with the formation of the transition shock wave (SW) region between the cascades. By varying the material of the outer array (tungsten wires or kapron fibers), it is shown that the plasma flow mode between the inner and outer arrays depends on the ratio between the plasma production rates min/mout in the inner and outer arrays. The obtained experimental results are compared with the results of one-dimensional MHD simulation of the plasma flow between the arrays. Stable implosion of the inner array plasma was observed in experiments with combined nested arrays consisting of a fiber outer array and a tungsten inner array. The growth rates of magnetic Rayleigh-Taylor (MRT) instability in the inner array plasma at different numbers of fibers in the outer array and different ratios between the radii of the inner and outer arrays are compared. Suppression of MRT instability during the implosion of the inner array plasma results in the formation of a stable compact Z-pinch and generation of a soft X-ray pulse. A possible scenario of interaction between the plasmas of the inner and outer arrays is offered. The stability of the inner array plasma in the stage of final compression depends on the character of interaction of plasma jets from the outer array with the magnetic field of the inner array. [ABSTRACT FROM AUTHOR]

An X-ray detector with a dielectric (KU1 optical glass) used as a sensitive element is described. Operation of the detector is based on the discovered effect of electric-field generation in a dielectric under exposure to radiation. The measurements were taken at the Angara-5-1 facility, at which the radiation source is megaampere Z-pinch plasma. It is shown that when the radiation power incident on the detector is approximately 1 MW/cm2, the detector response is a few volts with a time resolution of 1-2 ns. This effect is thought to be caused by “hot” electrons induced by radiation in the dielectric. The estimates for these experimental conditions are presented. [ABSTRACT FROM AUTHOR]

Results are presented from experimental studies of Z-pinches produced by implosion of aluminum and tungsten cylindrical wire arrays in the Angara-5-1 facility. The electron temperature T e and density n e of the high-temperature pinch plasma have been determined by analyzing line emission from multicharged ions. For the same mass and radius of the array and the same number of wires in it, the intensity of line emission of H- and He-like Al ions from an imploded Al + W wire array containing even a small amount of tungsten (7 wt %) is one order of magnitude lower than that from an Al array. As the W content increases, the total soft X-ray (SXR) yield increases, while the duration of the SXR pulse decreases. For the 30% W content in the array, the power and duration of the SXR pulse are nearly the same as those recorded during the implosion of a W array with the same linear mass and radius and the same number of wires. Results are also presented from experiments with nested wire arrays in which the outer and inner shells were made of Al and W wires, respectively. It is found that, in this case, the effect of tungsten on the line emission of aluminum is much weaker than that in experiments with arrays in which tungsten and aluminum wires were placed in the same shell, even if the mass of the inner (tungsten) shell was larger than that of the outer (aluminum) one. At the same time, the inner W shell plays a significant role in the implosion dynamics of a nested wire array, reducing the duration of the SXR pulse and increasing the SXR power. [ABSTRACT FROM AUTHOR]

The results of a study of a radiating Z-pinch with a profiled initial gas-density distribution over the z axis are presented. The gas distribution with the density maximum and transverse-size minimum at the discharge-gap center is formed by a pulsed gas valve with a specially designed nozzle. The parameters of X-ray radiation are measured for pinches formed in gaseous neon at currents of up to 200 kA. The experimentally selected gas density ensures the formation of a region with a typical size of less than 1 mm at the discharge-gap center. This region emits X-ray radiation in the keV photon-energy range in a time of less than 5 ns. Prospects for the development of an X-ray source based on this mechanism are discussed. [ABSTRACT FROM AUTHOR]

A study is made of the Z-pinch plasma expansion after the current is switched off. Measurements were carried out in experiments on the implosion of tungsten wire arrays in the Angara-5-1 facility. It is found experimentally that, at a distance of 2 m from the pinch, the ion velocity in the expanding Z-pinch plasma is about (2.5–4.0) × 107 cm/s, which substantially exceeds the thermal velocity of tungsten ions. A model describing the plasma expansion process is proposed that is based on the ambipolar acceleration mechanism. The results of numerical simulations are compared with the experimental data. [ABSTRACT FROM AUTHOR]

The set of diagnostic techniques used at the Angara-5-1 facility that make it possible to study the processes which accompany the ultrafast current-driven implosion of liners is described. This set includes electric methods and methods for the detection of various radiations. The liner-plasma shapes are visualized by detecting the intrinsic liner radiation in various wavelength ranges and actively probing liners in the visible and X-ray regions. Examples of the results of studying the current-driven implosion of cylindrical arrays of tungsten wires at the Angara-5-1 facility are presented. [ABSTRACT FROM AUTHOR]