A Wideband spectrometer for NMR studies

The design of a wideband decimeter-wave (200–900 MHz) spectrometer with a magnetic induction of up to ∼10 T is described. This spectrometer is intended for studying electronic-nuclear oscillations in antiferromagnets at low temperatures (4.2−1.3 K). Critical field H _c = 2.5 ± 0.3 T of a reorientation transition in a noncollinear antiferromagnet Mn₃Al₂Ge₃O₁₂ at temperature T ≈ 1.3 K was determined from a ⁵⁵Mn²⁺ NMR spectrum.     

A three-axes-compensated inductive magnetometer for measurements in high pulsed magnetic fields

A high-sensititity magnetometer intended for studying the magnetic properties of materials in pulsed magnetic fields of up to 43 T is described. A distinctive feature of the magnetometer is its method for compensating pickups generated in the magnetometer sensing element by a pulsed field. The commonly used uniaxial high-order compensation is replaced by a triaxial compensation of the lowest (quadrupole) order, combined with a transverse arrangement of the main probe coils. This method has allowed us to achieve a compensation level of the signal in the working coil (with an inner diameter of 1.4 or 1.75 mm) of the magnetometer without a sample of up to 10⁻⁶ for the longitudinal and 10⁻⁴ for the transverse field components. The magnetic moment sensitivity of the magnetometer is 10⁻⁴ mA·m² in fields below 10 T and 10⁻³ mA·m² at a field pulse amplitude of 35 T. A deviation of the compensation is below 2×10⁻⁴ for a temperature increase from 77 to 300 K and below 5×10⁻⁵ after sample replacement. The sample temperature is controlled by a fast-acting temperature control system in a range of 6–300 K to an accuracy of 0.3–0.05 K.     

Ion processes in a liquid-xenon ionization chamber under high-intensity pulsed irradiation

The current of positive ions in a liquid-xenon ionization chamber was studied under intense pulsed irradiation of the chamber with bremsstrahlung from a microtron. The dose absorbed in xenon during a radiation pulse was varied from 0.1 to 1.3 × 10⁴ μGy. It has been revealed that, in the dependence of the current on the irradiation dose, a deviation from a simple linear dependence is observed at a pulse dose of ∼4 μGy (∼0.2D _cr). Calculations show that recombination is the main cause of such deviation. A space charge appearing in the chamber under high irradiation intensities leads to a decrease in the electric field. The manifestation of the effects of a space charge becomes substantial when the field in a certain part of the chamber drops almost to zero. Under particular irradiation conditions, the space charge manifested itself in this study beginning with doses in a pulse of ∼50 μGy. The joint effect of the recombination and the space charge resulted in a dependence of the type of i ∼ D ^1/3. The influence of the ion current on the energy resolution of the ionization spectrometer is calculated for γ quanta detected during intervals between irradiation pulses. It is shown that a substantial impairment of the resolution begins at doses appreciably lower than the critical dose. The influence of the ion current becomes greater, as the dimensions of the chamber increase.     

Ultimate characteristics of an X-ray prism spectrometer

X-ray prism spectrometry schemes for experimental investigations of fast processes are considered. Diamond and beryllium prism dispersion parameters and special features of transmission spectra for crystal prisms are analyzed. It is shown that relative energy resolution E/ΔE at photon energies E ∼ 10 keV may reach 10³–10⁴ and the total working spectral band is ∼100 keV. This opens unique possibilities for measuring fine structures of single-shot absorption spectra for quasi-parallel beams and continuous monitoring of the fundamental and high-frequency harmonics of an X-ray free electron laser. Original Russian Text ? A.G. Tur’yanskii, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 4, pp. 150–158.     

A Sweeping Pulsed Radar–Reflectometer for Measuring the Electron Concentration Profile of Plasma

An instrument for measuring the electron concentration profile in magnetic confinement plasma devices is described. The instrument combines the advantages of rapidly tuned (sweeping) phase reflectometers and multichannel time-of-flight pulsed reflectometers and ensures measurements of the electron concentration profile at electron densities of 4.7 × 10¹²–4.5 × 10¹³ cm^–3 for 16 s.     

A two-frequency pulse refractometer for measuring the electron density in tokamaks

An instrument for fringe-jumps free measurements of the electron concentration and estimations of the peaking factor of density distributions in magnetic confinement plasma devices with probing at frequencies close to the cutoff is described. The instrument is intended to perform measurements in a 5 × 10¹⁸–10²⁰ m⁻³ density range (while probing by the extraordinary wave) with time resolution ∼10 μs.     

In-situ Vapor-Phase Lubrication of MEMS

In-situ vapor-phase lubrication of sidewall MicroElectroMechanical System (MEMS) devices is investigated with 1-pentanol vapor. The 1-pentanol vapor successfully maintains lubricating properties between silicon contacts of MEMS devices. This is attributed to the ability of alcohol to adsorb on the silicon surface and sustain a lubricating layer, which prevents wear of the MEMS surfaces and minimizes friction. In the presence of these vapors, MEMS devices with sliding contacts operated without failure for up to a factor of 1.7 × 10⁴ longer than in dry N₂ gas alone, representing a dramatic improvement in operating life. Adhesion and friction were also investigated as a function of alcohol vapor pressure. The adhesive force between microfabricated MEMS sidewall surfaces increases from ∼30 to ∼60 nN as the alcohol vapor pressure is increased from 0 to 20% of saturation, and then only slightly increases to ∼75 nN at 95% of saturation vapor pressure. This increase in force is well within the capabilities of even the lowest force on-chip actuators, such as electrostatic comb drives which can typically generate a few μN of force. The static friction force was found to be independent of alcohol vapor pressure within the uncertainties in the measurement.     

A subnanosecond pulsed source of electrons and X-rays

We measured the time and dose characteristics of electron and X-radiation of the иMA3-150З tube connected to the subnanosecond megavolt CпиH-2 accelerator. About ∼5×10¹² electrons per pulse are generated when the accelerating-voltage pulse is ≥600 kV high and ≈=0.3 ns long. The current amplitude reaches ∼5 kA, and the radiation dose is ∼5 kGy/pulse. The X-ray dose from the external tantalum target is 0.15 Gy/pulse. The development of the electron-tube and X-ray-tube prototypes with considerably smaller sizes has opened up new fields of application in medicine and engineering.     

Magnetic-field sensors based on lead-doped lanthanum manganites

The possibility of using lead-doped lanthanum manganites as materials for magnetically sensitive elements of sensors is considered. Measurements of the penetration coefficient of a radio-frequency electromagnetic field as a function of the strength of a stationary magnetic field have been performed. Two variants of using cores made from lanthanum manganites are analyzed. It is shown that cores made from lead-doped lanthanum manganites allow measurements of magnetic fields to be performed in the range 80?4 × 10⁶ A/m. A sensitivity of up to 2.5 × 10^?2%/A/m can be achieved for fields of 80?8 × 10³ A/m.     

A source of a high-power relativistic electron beam with high brightness

A ribbon diode of a U-2 accelerator (800 kV, ∼30 kA) intended for generating a high-intensity electron beam for heating plasma in a GOL-3 multimirror magnetic trap (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences) is described. The parameters of the beam characterized by a high brightness (∼7 kA/(cm² sr)) in a magnetic field of ∼5 T resulting from a numerical simulation of the beam formation process are presented. The results of simulation of the beam transport and transformation of the profile of its cross section during movement of electrons in a curvilinear guiding magnetic field are presented. The calculated cross section is compared to the beam imprint on a target.     

An air scintillator

A method for bremsstrahlung dosimetry by air luminescence at high-power pulsed electron accelerators is considered. Light emitted in an air scintillator is focused by the lens at the tip of a quartz optical fiber and transmitted to the photocathode of a photomultiplier tube. The sensitivity of the measuring channel is determined using a standard ribbon lamp. Bremsstrahlung pulses producing an exposure of 0.18 C/kg at the bremsstrahlung beam axis in a ∼20-ns time interval are detected at the ЛИУ-30 electron accelerator with a high accuracy. This exposure corresponds to an absorbed dose rate, integrated over the beam diameter, of 7.5 × 10⁷ Gy m/s.     

A source of broad homogeneous beams of low-energy (∼0.5 keV) gas ions

A source of gas ions (argon, oxygen, nitrogen, etc.), the operating principle of which is based on the use of a glow discharge in an electrode system of a wide-aperture hollow cathode and anode in a magnetic field, is described. The exit aperture diameter of the hollow cathode, increased up to a size close to the ion beam diameter (10 cm), ensures the uniform ion emission of the plasma generated in the discharge region near the anode. A decreased angular divergence or increased ultimate ion-beam current density is achieved by a change in the potential drop in the space charge sheath between the plasma and the ion optics. The source generates broad (50 cm²) slightly diverging (ω/2∼3°–5°) ion beams with energies of 300–1000 eV at a beam current density of ∼0.5 mA/cm².     

An experimental setup for studying neutron-neutron final state interaction on the neutron channel of the Moscow Meson Factory

A setup for measuring the singlet nn-scattering length in the n + d → p + n + n reaction is described. It is composed of a neutron hodoscope with an angular aperture of 12° and a scintillation detector for protons escaping at an angle of 90° with the beam direction. The exit angles and the energies of a proton and both neutrons are measured. The neutron energies are measured using the time-of-flight method. At a time resolution of ∼0.6 ns and a flight base of ∼5.5 m, the accuracy in measuring the neutron energy is ∼1% at an energy of ∼15 MeV. The dependence of the reaction yield on the relative energy of two neutrons is investigated. The neutron-neutron final-state interaction manifests itself as a peak in this distribution.     

A plasma generator based on nonself-sustained low-pressure glow discharge with a large-volume hollow cathode

The results of studying nonself-sustained glow discharges in an electrode system with a hollow cathode with a volume of 0.25 m³ are presented. A high-current (up to 35 A) nonself-sustained glow discharge at low pressures (0.3–1.0 Pa) is initiated and sustained with the help of an auxiliary cold-hollow-cathode arc discharge. When the current of a nonself-sustained glow discharge increases from 2 to 35 A, its burning voltage changes from 40 to 300 V. These values are much lower than the voltage for a self-sustained glow discharge in the same electrode system. At a discharge current of 30 A, the electron concentration at the center of the hollow cathode is n _e ∼ 10¹⁰–10¹¹ cm⁻³ and the electron temperature is T _e ≈ 2 eV. The discharge considered can be used in the system for modification of materials and products.     

A low-temperature capacitive dilatometer

A dilatometer with a capacitive displacement sensor intended for measuring the thermal expansion of solid samples in a temperature range of 4–300 K is described. The sensor of the instrument was mounted inside of industrial insert VTI SIV with controlled circulation of liquid helium encased in portable cryostat and was successfully used jointly with a simple commercial temperature control system. The dilatometer allows studies of the thermal expansion of samples with a sensitivity of ∼1.4 ? in consecutive cooling and warming cycles with a rate of ∼10⁻³ K/min. The results of measuring the thermal expansion of a CoS₂ sample near the phase-transition point are presented.     

Highly-sensitive analog magnetometer based on a null-picovoltmeter

The principle of measurement of small magnetic moments using superconducting null-picovoltmeter (SNPV) is described. It is shown that in the mode with optimal voltage sensitivity (≥10^–12 V), the sensitivity of SNPV to a magnetic moment can reach 10^–8 emu, the level only implemented in SQUIDs. An example is given of using SNPV to measure the magnetic susceptibility of superconducting diamagnetic and paramagnetic samples, approximately 1 mm³ in volume, with different signs of the magnetization in the magnetizing alternating magnetic fields with induction of about 1 G, at low temperatures.     

High-Sensitivity Magnetometers Based on HTSC Ceramics

The magnetic response of the YBa₂Cu₃O_{7 – x} superconducting ceramics to an alternating magnetic field was studied experimentally. A magnetometer with a sensitivity level of 2 × 10^–7Oe was developed on the basis of the experimental data. The ways of improving such devices are discussed.     

A Setup for Measuring Magnetic Properties of Magnetically Soft Materials in the Pulsed Remagnetization Regime

The modern technological level and trends of the development of magnetic techniques for measuring properties of magnetically soft materials (MSM) used in setups in whose cores magnetization is reversed in the pulsed regime have briefly been reviewed. A setup for measuring magnetic properties of MSM in a pulsed remagnetization regime for the pulse duration of 1–100 s and the magnetic flux of 10^–8–10^–5 Wb is described.     

Resistive loss compensation in the power supply system of the toroidal field winding in the TUMAN-3M tokamak

In the tokamak, in which the winding generating the toroidal field with induction B _t is powered from an inductive energy storage, resistive losses are the main factor that causes B _t to decrease during a discharge. Upgrading of the power supply circuit of the toroidal magnetic field winding (TFW) in the TUMAN-3M tokamak is aimed, primarily, at increasing B _t in the injection heating phase and, second, at maintaining B _t quasi-stationarity during the whole tokamak discharge. To do this, an additional two-section capacitive storage commuted by two thyristor switches has been introduced into the available circuit. Either section of the storage is characterized by a charging voltage of 0.25 kV, a capacitance of 4.32 F, and an energy capacity of 135 kJ. The maximum discharge current of the section is 40 kA. The upgraded circuit compensates for the resistive loss in the TFW and ensures thereby a 50% increase in the magnetic field during injection heating relative to the old circuit: B _t = 1.0 T instead of 0.68 T. In this case, the circuit maintains a TFW current of 110 kA with an accuracy of 10% for ∼60 ms.     

A compact vacuum UV excilamp on argon dimers

The energy and spectral characteristics of the argon dimer emission with the maximum at a wave-length of ∼126 nm under excitation by a pulse-periodic discharge in a gas flow with pressures higher than the atmospheric pressure are studied. A compact excilamp has been designed for obtaining radiation in the vacuum ultraviolet spectrum region. The minimal argon flow velocities are determined, at which cooling is effected by convective gas ejection from the discharge region. This allows one to form a diffusion discharge with a stable radiation power density. It is shown that, when the flow velocity is 0.5 m³/h, the radiation power density of an Ar₂* molecule is >100 μW/cm² behind a LiF window with ∼10% transmission at a wavelength of 126 nm. It is shown that the use of a windowless design and an increase in the gas flow velocity allows an increase in the radiation power density up to 10 mW/cm².