A comparative study of the effect of irradiation with helium ions on the optical properties of single-crystal molybdenum mirrors with crystallographic orientations 〈110〉 and 〈111〉 is presented. The ...irradiation mode corresponds to the conditions in the built-in systems for plasma cleaning of the input mirrors from contamination in the optical diagnostics of the ITER international thermonuclear reactor using helium as a working gas. Such irradiation results in a variation in the specular reflection and diffuse scattering of the mirror that is virtually independent of the initial structure of the surface layer of the mirror and the duration of the irradiation process. The authors explain the changes of the optical characteristics of the mirror using the formation of nanosized bubbles in the surface skin layer. The Rayleigh scattering of incident radiation by the bubbles leads to a decrease in the intensity of specular reflection and an increase in the diffuse scattering. A model of the formation and growth of nanosized bubbles and their effect on optical properties is proposed. The results must be taken into account in the analysis of experimental data in the ITER optical diagnostics after removing of contaminants using helium, when choosing a working gas for plasma cleaning systems for mirrors, and also for the formation of a nanoporous structure in a thin surface layer of metals.
Contamination of ITER in-vessel components in accidents associated with the ingress of water from the cooling system into the vacuum vessel poses a threat to subsequent operation of the entire ...facility and individual diagnostic systems. In the present study, the process of degradation of the optical properties of single-crystal Mo mirrors, which are used in optical diagnostics, in their interaction with liquid water and water vapor is examined. The dynamics of variation of the specular reflection and diffuse scattering coefficients with exposure time and interaction mode is studied experimentally. It is demonstrated that the worst-case scenario (“steam event” in the ITER documentation) is modeled accurately by mirror exposure to distilled water at a temperature of ≈97°C. Samples of Mo mirrors with simulated contamination obtained in these experiments are used to test the operation of the plasma mirror cleaning system based on a direct- or pulsed-current abnormal glow discharge in a grid hollow cathode. It is demonstrated that the optical quality of Mo mirrors contaminated in simulated emergency events with water entering the vacuum vessel may be restored to near-baseline levels if Ar is used as the plasma-forming gas.
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The dependence of the sputtering efficiency for a Mo mirror mock-up on the discharge power and the pressure of the working gas (Ar) has been investigated for three options of grounding of the ...discharge-cell elements in the plasma cleaning system. A gas discharge with a direct current or medium-frequency pulsed current is expected to be used to clean the entrance mirror of CXRS-edge (Active Spectroscopy) diagnostics of ITER. By selecting the electrode-grounding scheme it is possible to obtain different degrees of deceleration of ions that leave the discharge cell and are able to sputter the walls of the diagnostic port. The location of the diagnostic-port walls in close vicinity to the discharge cell and the absence of a working-gas flow through the region of the cleaning discharge are the specific features of the mirror cleaning systems in ITER. These conditions have been simulated by placing a full-scale functional model of the discharge cell into a leaky gas-dynamic fairing, which was made of stainless steel, like the walls of ITER diagnostic port. It is shown that the highest cleaning efficiency is attained when the cathode elements of the discharge cell and the entrance mirror in particular are electrically isolated from the diagnostic-port walls. These results can be used to develop plasma cleaning systems for other optical diagnostics of ITER.
The results of a study of the effects of a gas flow through the discharge region and the location of the diagnostic port walls close to the discharge cell on the efficiency of the plasma system for ...cleaning the entrance mirror of the Active Spectroscopy optical diagnostics, which have been developed in Russia for the ITER reactor, are presented. The experiments were carried out on a full-size functional model of a discharge cell operating on a constant or unipolar pulse current, electrically isolated from the walls of the vacuum chamber. The material of the model of the entrance mirror is molybdenum. The working gas is argon. A vacuum unit with dynamic stabilization of the working gas pressure was used. The absence of a gas flow through the discharge region and the proximity of the ITER diagnostic port walls to the discharge cell were simulated by placing the discharge cell inside a box-shaped gas-dynamic fairing placed in a vacuum chamber. Experiments with a gas flow at a large distance from the discharge cell to the walls of the vacuum chamber were carried out without using a fairing. It was revealed that the absence of a gas flow at a small distance of the discharge cell elements from the walls of the vacuum chamber increases the cleaning efficiency.
The intravacuum mirrors used in the systems of optical plasma diagnostics on fusion installations are subject to contamination and require periodic cleaning. It is proposed to clean the mirrors by ...ion sputtering of the impurity from the reflective surface in a gas discharge. In this work, results are presented from experimental studies of the possibility of controlling the mirror cleaning process in the glow discharge localized inside a grid hollow cathode and controlled by direct current (DC) or mid-frequency pulsed direct current (MDC). Three independent methods of control were studied: measurements of the voltage of the cleaning discharge at a fixed current, measurements of the frequency of the appearance of microarc couplings in the presence of dielectric contaminants, and emission spectroscopy studies of the cleaning discharge. Separately, to verify the cleaning effect, results were presented from measuring the reflection spectrum of the mirror. It was shown that all three methods can be used in the cleaning systems. The first of the discussed methods appears to be the most promising since it does not require additional detectors and uses only the data obtained from the discharge power supply unit, and it is applicable to cleaning mirrors from both current-conducting and thin dielectric contaminations. The control based on measuring the frequency of appearance of microarc couplings can be used when one alternates between the PDC and the DC regimes in the presence of layered metal–dielectric contaminations and cleaning the local dielectric contaminations resulting from emergencies. The spectroscopic control method provides the highest sensitivity and allows one to determine the composition of the contaminants, yet it also has higher requirements for the recording equipment. The considered methods can be used to automate the processes of removing the contamination in the systems for plasma cleaning of the input diagnostic mirrors of fusion installations and to control the finishing treatment of substrates before vacuum deposition of coatings.
The rotor blades of the helicopter are operated on the principle of ensuring operability within the assigned resource, which is 2000 flight hours, after which they are subject to decommissioning. ...However, by the end of this period, as a rule, fatigue damage does not have time to propagate in the blade, so it can be operated on. Thus, the study of the process of nucleation and propagation of fatigue cracks in the blades will allow to determine the period during which the presence of cracks does not threaten the performance of the construction. This will make suggestions for a possible increase in the assigned resource of the blade, which, in turn, will lead to cost savings. The problem of the work is to study the propagation of fatigue cracks in the rotor blades of a helicopter to make recommendations on the possible increase in their assigned resource. Research objectives: development of methodology for full-scale testing of blades; determination of their endurance limit; development of a methodology for processing the results of full-scale tests (videos of the growth of fatigue cracks); assessment of the possibility of extending the assigned resource of the blades. Experimental methods of fracture mechanics and statistical methods for processing data obtained during experiments were used as research methods. As a result, it was found that the appearance and propagation of surface cracks in the blades with the test base of N = 1.6⋅107 cycles begin after the stresses exceed the level of 76.94 MPa. A fatigue crack in the blades propagates to failure within 150...170 hours, while the subcritical propagation of the crack lasts 130...150 hours. The period of stable slow propagation of cracks can be proposed for inclusion in the assigned resource of the blade.
The results of experimental investigations of the angular distributions during magnetron sputtering of Mg, Al, Si, Ti, Cr, Cu, Zn, Ge, Zr, Nb, Mo, Ag, In, Sn, W, Pt, Au, and Bi targets in argon at a ...constant current are presented. The operating conditions during the experiments corresponded to the values typical of industrial sputtering equipment. The angular distribution of the material flow was calculated based on the measured thickness of the coating deposited on two flexible ribbon substrates. These substrates were fixed in place on a substrate holder in the form of two crossed half-rings that were equidistant from the center of the magnetron target (the curvature radius was 100 mm). The influence of the magnitude and shape of the magnetic field near the surface of the sputtered cathode on the angular distribution was also investigated. The results can be used as the source data for calculating the profile of the coating during magnetron sputtering.
The results of a study into the limiting operating conditions for gas pressure when using D
2
, He, Ne, and Ar in the “Active spectroscopy” diagnostic plasma cleaning system for the input mirror of ...the ITER reactor are presented. The experiments were carried out on a full-sized functional model of a cleaning system based on a discharge with a mesh hollow cathode, with all cathode elements of the discharge cell grounded, including a full-size model of the input mirror. It was found that, when using D
2
, He, and Ne as working gases, the ignition pressure at a voltage of 750 V is approximately 60, 100, and 20 Pa, respectively, and significantly exceeds the maximum allowable for ITER in the cleaning mode (7 Pa). In this case, the discharge quenching pressure in the considered cases is ≤1 Pa. It is shown that the use of an additional thermionic cathode located inside the discharge cell makes it possible to initialize the discharge at pressures close to the quenching pressure. Turning on the hot cathode with a smooth increase in the heating current in the absence of a discharge current and turning it off after ignition of the discharge provide a significant increase in the life of the hot cathode. The applicability of all gases available for use in ITER and a radical reduction in the operating pressure facilitates the solution of the problem of degassing the vacuum chamber and diagnostic ports of thermonuclear facilities after cleaning the mirrors, which makes it possible to reduce the proportion of heavy impurities in the deuterium–tritium mixture and, accordingly, to increase the plasma temperature during operation impulse.
In this paper, we discuss the results of applying a tagged neutron method for a remote nondestructive analysis of the elemental composition of matter on a conveyor. The tagged neutron method consists ...in irradiating the test substance with fast neutrons with an energy of 14 MeV, followed by recording the characteristic radiation of gamma quanta. Neutron tagging is carried out by an alpha detector built into the neutron generator.
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