A Plasma Reactor for the Synthesis of High-Temperature Materials: Electro Thermal, Processing and Service Life Characteristics

The three-jet direct-flow plasma reactor with a channel diameter of 0.054 m was studied in terms of service life, thermal, technical, and functional capabilities. It was established that the near-optimal combination of thermal efficiency, required specific enthalpy of the plasma-forming gas and its mass flow rate is achieved at a reactor power of 150 kW. The bulk temperature of plasma flow over the rector of 12 gauges long varies within 5500±3200 K and the wall temperature within 1900±850 K, when a cylinder from zirconium dioxide of 0.005 m thick is used to thermally insulate the reactor. The specific electric power reaches a high of 1214 MW/m{3}. The rated service life of electrodes is 4700 hours for a copper anode and 111 hours for a tungsten cathode. The projected contamination of carbides and borides with elec-trode-erosion products doesn't exceed 0.0001% of copper and 0.00002% of tungsten

Measurement of the energy resolution and calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip

This paper describes an iterative method of per-pixel energy calibration of hybrid pixel detectors with GaAs:Cr sensor and Timepix readout chip. A convolution of precisely measured spectra of characteristic X-rays of different metals with the resolution and the efficiency of the pixel detector is used for the calibration. The energy resolution of the detector is also measured during the calibration. The use of per-pixel calibration allows to achieve a good energy resolution of the Timepix detector with GaAs:Cr sensor: 8% and 13% at 60 keV and 20 keV, respectively

Interacting circular nanomagnets

Regular 2D rectangular lattices of permalloy nanoparticles (40 nm in diameter) were prepared by the method of the electron lithography. The magnetization curves were studied by Hall magnetometry with the compensation technique for different external field orientations at 4.2K and 77K. The shape of hysteresis curves indicates that there is magnetostatic interaction between the particles. The main peculiarity is the existence of remanent magnetization perpendicular to easy plain. By numerical simulation it is shown, that the character of the magnetization reversal is a result of the interplay of the interparticle interaction and the magnetization distribution within the particles (vortex or uniform).Comment: 16 pages, 8 figure

Optical conductivity and penetration depth in MgB2

The complex conductivity of a MgB2 film has been investigated in the frequency range 4 cm^{-1}< nu < 30 cm^{-1} and for temperatures 2.7 K < T <300 K. The overall temperature dependence of both components of the complex conductivity is reminiscent of BCS-type behavior, although a detailed analysis reveals a number of discrepancies. No characteristic feature of the isotropic BCS gap temperature evolution is observed in the conductivity spectra in the superconducting state. A peak in the temperature dependence of the real part of the conductivity is detected for frequencies below 9 cm^{-1}. The superconducting penetration depth follows a T^2 behavior at low temperatures.Comment: 4 pages, 4 figure

Considerable enhancement of the critical current in a superconducting film by magnetized magnetic strip

We show that a magnetic strip on top of a superconducting strip magnetized in a specified direction may considerably enhance the critical current in the sample. At fixed magnetization of the magnet we observed diode effect - the value of the critical current depends on the direction of the transport current. We explain these effects by a influence of the nonuniform magnetic field induced by the magnet on the current distribution in the superconducting strip. The experiment on a hybrid Nb/Co structure confirmed the predicted variation of the critical current with a changing value of magnetization and direction of the transport current.Comment: 6 pages, 7 figure

Performance of the Scintillator System Prototype of the NUCLEON Space Experiment

Abstract The NUCLEON space experiment has been proposed to perform direct measurements of CR energy spectrum and composition up to E ∼ 10 15 eV. The NUCLEON detector consists of layers of different detectors: scintillator detectors with WLS fibers and silicon pad and microstrip ones. The results of beam and space qualification tests of the scintillator detectors are presented

Anisotropic conductivity of Nd_{1.85}Ce_{0.15}CuO_{4-\delta} films at submillimeter wavelengths

The anisotropic conductivity of thin Nd$_{1.85}$Ce$_{0.15}$CuO$_{4-\delta}$ films was measured in the frequency range 8 cm$^{-1}<\nu <$ 40 cm$^{-1}$ and for temperatures 4 K $<T<300$ K. A tilted sample geometry allowed to extract both, in-plane and c-axis properties. The in-plane quasiparticle scattering rate remains unchanged as the sample becomes superconducting. The temperature dependence of the in-plane conductivity is reasonably well described using the Born limit for a d-wave superconductor. Below T_{{\rm C}%} the c-axis dielectric constant $\epsilon_{1c}$ changes sign at the screened c-axis plasma frequency. The temperature dependence of the c-axis conductivity closely follows the linear in T behavior within the plane.Comment: 4 pages, 4 figure

Magnetization curves for two-dimensional rectangular lattices of permalloy nanoparticles: experimental investigation and numerical simulation

Abstract This work is concerned with the behaviour of a regular 2D rectangular lattice of Ni 3 Fe nanoparticles, determined by the dipole interaction between them. The samples under study, prepared by electron-beam lithography, consisted of about 10 5 particles approximately 50 nm in size. The magnetization curves were studied by Hall magnetometry for different external magnetic field orientations at 4.2 K and 77 K. The results indicate a collective behaviour of the system. The magnetization curves depend on the external magnetic field direction and temperature; the system exhibits multistability. A model system of interacting 3D magnetic dipoles forming a rectangular lattice was numerically simulated by solving a system of stochastic Landau-Lifshitz equations. The multistability of the system and steps in the magnetization curves were obtained. It is shown analytically that the shape of the magnetization curves depends on the character of the interaction in the system

ОСОБЕННОСТИ ЭЛЕКТРООСАЖДЕНИЯ КОМПОЗИЦИОННЫХ ПОКРЫТИЙ «НИКЕЛЬ–НАНОПОРОШОК ДИБОРИДА ХРОМА»

The conditions for obtaining composite electrochemical coatings (CEC) have been investigated on the basis of nickel with the use of CrB2 nanopowder as a hardening phase in standard nickel-plating electrolyte. It is established that the maximum saturation of the nickel matrix in using chromium nanoboride takes place when its concentration in the electrolyte is 5–10 kg/m3 that is 8–12 times lower than in using micropowders. CEС microhardness of Ni–CrB2(nano) composition with the content of 0,59–0,65 % hardening phase is 1,16–1,19 times higher than that of Ni–CrB2(micro) coatings containing 2,47–2,86 % boride and 1,64–1,86 times higher than that of the nickel matrix. The optimum conditions of CEC deposition are cathodic current density of 1,0 kA/m2, nanoboride concentration of 5–10 kg/m3 in the electrolyte, pH 5,0–5,5, and temperature of 323 K.Исследованы условия получения композиционного электрохимического покрытия (КЭП) на основе никеля с использованием в качестве упрочняющей фазы нанопорошка CrB2 в стандартном электролите никелирования. Установлено, что максимальное насыщение никелевой матрицы при использовании наноборида хрома происходит при его концентрации в электролите 5–10 кг/м3, что в 8–12 раз ниже, чем при добавке микропорошков CrB2. Микротвердость КЭП состава Ni–CrB2(нано) при содержании в них упрочняющей фазы 0,59–0,65 % в 1,16–1,19 раз выше, чем у покрытий Ni–CrB2(микро), содержащих 2,47–2,86 % борида, и в 1,64–1,86 раз выше, чем у никелевой матрицы. Оптимальными условиями осаждения КЭП являются: катодная плотность тока 1,0 кА/м2, концентрация наноборида в электролите 5–10 кг/м3, рН = 5,0÷5,5 и температура 323 К