Low-symmetry paramagnetic center in a KTaO<Subscript>3</Subscript>: Ni crystal

A new paramagnetic center of orthorhombic symmetry with spin S = 1/2 is revealed in KTaO₃: Ni crystals. The well-resolved superhyperfine EPR structure consisting of 15 components indicates preferred interaction of the center with two tantalum nuclei (¹⁸¹Ta, I = 7/2). This center does not decay and its orientation remains unchanged up to room temperature. Possible models of the center are discussed.     

The Topography of Surface and Light Transmission by Quartz Windows after Exposure in a High-Frequency Discharge in Deuterium and Mixture of Deuterium with Nitrogen

Technical Physics - The effect of a high-frequency discharge on the change in the topography of the surface of KU-1 optical quartz and transmission of visible light (400–1000 nm) is studied....     

Thomson scattering diagnostics in the Globus-M tokamak

Specific features of the Thomson scattering diagnostics, its main characteristics and capabilities, and the results of its experimental testing in the Globus-M tokamak are described. A powerful multipulse neodymium-glass laser is designed for investigating both fast and slow processes in the tokamak plasma. The laser is capable of generating up to 20 pulses uniformly distributed in time during one tokamak discharge. In order to investigate fast transient processes, the laser repetition rate can be increased within a specified time interval. The possibility of varying the time interval between laser pulses from 0.5 ms to 1.0 s makes this diagnostics highly informative. The optical scheme developed in the course of these studies allowed one to simplify the power supply system and create a comparatively inexpensive laser system. The use of avalanche photodiodes and filtering polychromators with a high optical transparency provides high sensitivity of the diagnostics. A special software was designed that allows automatic processing of several hundred signals during one shot and provides data on the electron density and temperature immediately in the course of measurements. The diagnostics allows one to trace the time behavior of the spatial profiles of the electron temperature and density in both ohmic discharges and discharges with auxiliary heating, as well as in experiments with particle injection with a plasma gun.     

Electric-field-induced orientation of iron tetragonal centers in KTaO3

Fe _K ³⁺ -O _i ^2? impurity centers in a KTaO₃ sample to which a dc electric field E=75 kV/cm is applied are shown to be oriented at temperatures T≥120 K. In these conditions, the effective local field acting on the electric dipole moment of a center exceeds the applied field by a factor 7.6.     

The sensitivity of photoemulsions and its relation to the sensitivity of a photocathode

The sensitivity limitations arising from fluctuations in photoemulsions are discussed and the conditions under which the limitations reach a minimum are described. The photoemulsion area which corresponds to a minimum number of quanta at a certain registration accuracy is derived. Estimates are given which indicate how the required light sum increases when the area exceeds the optimum value. The sensitivities of photoemulsions and photocathodes are compared. It could be shown that the photoemulsion sensitivity deteriorates to a certain extent when the exposure range increases. A selection of the exposure working region is suggested which, in contrast to the linear portion of the characteristic curve, permits measuments with a smaller light input and in a wider exposure range.     

Blistering of mechanically polished molybdenum upon its exposure to deuterium-containing plasma

Recent data on the blistering process in polished polycrystalline Mo for the case of direct-current glow discharge in deuterium and D₂/2–4 mol % O₂ or N₂ admixtures, at an energy of incident molecular ions of 70–120 eV and a pressure of 14 Pa, are reported. Depending on the method of metal surface polishing, the initial metal grains are broken up into mutually disordered regions of smaller sizes (subgrains); the chemical composition of the damaged layer changes. In the formed structure, blistering can develop easily or be impeded. Small additions of O₂ or N₂ to deuterium facilitate the blistering.     

Formation of Films of Tungsten and its Oxides in a High-Frequency Capacitive Discharge in a D<Subscript>2</Subscript>-O<Subscript>2</Subscript> Mixture

A technique for tungsten-film deposition on different substrates in asymmetrical high-frequency (1.76 MHz) capacitive discharge in a D₂?6.5 mol % O₂ mixture under a total pressure of 15 Pa and at 60–130°C is considered. A circular W strip near the upper inner edge of a cylindrical hollow cathode with a radius of 4.2 cm and a height of 10 cm is the source of W particles. The smooth transition from sputtering of the inner surface to deposition occurs at a distance of about 4 cm from the upper boundary of the open part of the cathode. W, Mo, ZrO₂, Si, and Cu substrates are placed in the lower closed end (bottom) and on the inner lateral cathode surface. At the upper cathode edge the sputtering yield is (4–5) × 10^?2 at/ion. The mass rate of W deposition on the cathode bottom does not depend on the substrate type and is 40 μg/(cm² h). The peculiarities of the composition, morphology, and structure of W films obtained on the lateral surface and bottom of the hollow cathode are discussed.     

Silicon photodiodes as Thomson scattering detectors in experiments on the Tuman-3M tokamak and in bench experiments

Experiments on Thomson scattering in the Tuman-3M tokamak plasma with silicon photodiodes applied as radiation detectors are performed. Bench tests and numerical simulation are used to compare the efficiency of detector modules based on conventional and avalanche photodiodes in recording weak pulses of various durations against uniform background light. When the pulse duration increases to several hundreds of nanoseconds, the increase in sensitivity due to avalanche gain disappears. This is of importance for diagnosing the tokamak plasma, where the background radiation is relatively intense.