A neutron field monitoring system for collider experiments

A monitoring system for intense (up to 10⁵ neutrons/(cm² s)) neutron fluxes with energies as high as 15 MeV has been developed for long-term operation in strong magnetic and radiation fields of collider experiments. The system is used to monitor the radiation shielding efficiency, estimate the radiation degradation of active elements of experimental setups, and perform additional independent monitoring of the accelerator luminosity. The system has been tested and put into operation at the Compact Muon Solenoid (CMS) experimental setup of the Large Hadron Collider (LHC).     

Experimental setup for laser spectroscopy of molecules in a high magnetic field

An experimental setup to measure the effects of a high magnetic field on the structure and decay dynamics of molecules is designed and constructed. A vacuum chamber is mounted in the bore of a superconducting magnet. A molecular beam passes in the chamber. Pulsed laser light excites the molecules in the field. The parent or fragment ions are extracted by an electric field parallel to the magnetic field. They are detected by a microchannel plate. Their mass and charge are determined by the time-of-flight method. The performance of the setup was examined using resonance-enhanced two-photon ionization through the X(2)?Π-A(2)Σ(+) transition of nitric oxide (NO) molecules. The ions were detected with sufficient mass resolution to discriminate the species in a field of up to 10 T. This is the first experiment to succeed in the mass-selective detection of ions by the time-of-flight method in a high magnetic field. By measuring NO(+) ion current as a function of the laser frequency, the X(2)Π-A(2)?Σ(+) rotational transition lines, separated clearly from the background noise, were observed in fields of up to 10 T. From the relative strengths of the transition lines, the ion detection efficiency was determined as a function of the magnetic field strength. This setup was shown to be applicable in a field higher than 10 T. The Landau levels of molecules were successfully observed to demonstrate the setup.     

Synchronized time- and high-field-resolved all-optical pump-probe magneto-optical setup based on a strong alternating magnetic field and its application in magnetization dynamics of high coercivity magnetic medium

An alternating magnetic field (AMF) apparatus is developed and composed of an electromagnet and driving power supply. The structure of the electromagnet and configuration of the driving supply are described in detail. The apparatus can produce a peak magnetic field up to 9000 Oe and above under a small driving power at its resonance frequency of 1.14 kHz. Based on synchronization between the AMF and the femtosecond laser pulse train, a photomagnetic synchronized time- and high-field-resolved all-optical pump-probe magnetic-optical setup is developed. This setup has the ability to reinitialize any magnetic states between two successive laser pulses so that irreversible magnetization reversal dynamics can be studied. Dynamic Kerr hysteresis loops and magnetization reversal dynamics of high coercivity ferromagnetic TbFeCo and FePt films are demonstrated using this setup, showing importance of this synchronized time- and high-field-resolved all-optical pump-probe magnetic-optical setup in the research of ultrafast magnetization dynamics.     

Development of the large neutron imaging system for inertial confinement fusion experiments

Inertial confinement fusion (ICF) requires a high resolution (~10 μm) neutron imaging system to observe deuterium and tritium (DT) core implosion asymmetries. A new large (150 mm entrance diameter: scaled for Laser Me?gaJoule [P. A. Holstein, F. Chaland, C. Charpin, J. M. Dufour, H. Dumont, J. Giorla, L. Hallo, S. Laffite, G. Malinie, Y. Saillard, G. Schurtz, M. Vandenboomgaerde, and F. Wagon, Laser and Particle Beams 17, 403 (1999)]) neutron imaging detector has been developed for such ICF experiments. The detector has been fully characterized using a linear accelerator and a (60)Co γ-ray source. A penumbral aperture was used to observe DT-gas-filled target implosions performed on the OMEGA laser facility. [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)] Neutron core images of 14 MeV with a resolution of 15 μm were obtained and are compared to x-ray images of comparable resolution.     

Development of effective power supply using electric double layer capacitor for static magnetic field coils in fusion plasma experiments

A cost-effective power supply for static magnetic field coils used in fusion plasma experiments has been developed by application of an electric double layer capacitor (EDLC). A prototype EDLC power supply system was constructed in the form of a series LCR circuit. Coil current of 100 A with flat-top longer than 1 s was successfully supplied to an equilibrium field coil of a fusion plasma experimental apparatus by a single EDLC module with capacitance of 30 F. The present EDLC power supply has revealed sufficient performance for plasma confinement experiments whose discharge duration times are an order of several seconds.     

Elastic incoherent neutron scattering operating by varying instrumental energy resolution: principle, simulations, and experiments of the resolution elastic neutron scattering (RENS)

The main aim of this paper is to present the scientific case of the resolution elastic neutron scattering (RENS) method that is based on the collection of elastic neutron scattering intensity as a function of the instrumental energy resolution and that is able to extract information on the system dynamical properties from an elastic signal. In this framework, it is shown that in the measured elastic scattering law, as a function of the instrumental energy resolution, an inflection point occurs when the instrumental energy resolution intersects the system relaxation time, and in an equivalent way, a transition in the temperature behavior of the measured elastic scattering law occurs when the characteristic system relaxation time crosses the instrumental energy resolution time. With regard to the latter, an operative protocol to determine the system characteristic time by different elastic incoherent neutron scattering (EINS) thermal scans at different instrumental energy resolutions is also proposed. The proposed method, hence, is not primarily addressed to collect the measured elastic scattering intensity with a great accuracy, but rather relies on determining an inflection point in the measured elastic scattering law versus instrumental energy resolution. The RENS method is tested both numerically and experimentally. As far as numerical simulations are concerned, a simple model system for which the temperature behavior of the relaxation time follows an Arrhenius law, while its scattering law follows a Gaussian behavior, is considered. It is shown that the system relaxation time used as an input for the simulations coincides with the one obtained by the RENS approach. Regarding the experimental findings, due to the fact that a neutron scattering spectrometer working following the RENS method has not been constructed yet, different EINS experiments with different instrumental energy resolutions were carried out on a complex model system, i.e., dry and D(2)O hydrated lysozyme, in an extended temperature range. The resulting temperature behavior of the system relaxation time, obtained with RENS method, agrees very well with the one obtained in literature, for the same system, following the quasi-elastic neutron scattering (QENS) approach. The proposed scientific case puts into evidence the challenges of an RENS spectrometer working by varying the instrumental energy resolution; in particular, in comparison with QENS, the proposed RENS method requires a smaller amount of sample, which is an important point in dealing with biological and exotic systems; it is not affected by the use of model functions for fitting spectra as in QENS, but furnishes a direct access to relevant information.     

A gated liquid-scintillator-based neutron detector for fast-ignitor experiments and down-scattered neutron measurements

The detection of neutrons in fast-ignitor experiments or down-scattered neutrons in inertial fusion experiments is very challenging since it requires the neutron detection system to recover within 10-100 ns from a high background orders of magnitude stronger than the signal of interest. The background is either the hard x-ray emission from short-pulse laser target interactions for the fast-ignitor experiments or the primary neutron signal for the down-scattered neutrons. A liquid-scintillator detector has been developed using a gated photomultiplier that suppresses the background signal and eliminates the afterglow present in conventional plastic scintillators.     

Development of a variable temperature mechanical loading device for in situ neutron scattering measurements

Understanding the phase transformation and failure mechanism of NiTi shape memory alloys under variable environments of high and low temperatures is critical to the establishment of constitutive properties and to the realization of controllable design. Information regarding the correlation between the phase transformation and deformation can be obtained by in situ neutron scattering measurements. Therefore, a variable temperature mechanical loading device is designed, which can be used for mechanical loading and in situ neutron scattering measurements in a variable temperature environment. Specifically, the device can achieve precise temperature control with a temperature change from −55 °C to 200 °C in a protective atmosphere. The rated load in the axial direction is 6 kN, and the maximum displacement of the unilateral grip is larger than 30 mm. In situ neutron scattering measurements can be performed through neutron windows, and the strain can be measured by digital image correlation technology. Moreover, the force sensor is calibrated to improve test precision. Through an evaluation of temperature uncertainty, the temperature measurement performance is estimated. Tensile tests of the NiTi alloy at variable temperatures are carried out, and preliminary results are given. The four deformation stages of the NiTi alloy can be seen from the stressstrain curve, which corresponds to the existing results. This demonstrates that the designed variable temperature mechanical loading device can supply the testing demands. The device provides a new way to study the relationship between the phase transformation and mechanical properties of NiTi shape memory alloys at variable temperatures.

     

A novel approach for x-ray scattering experiments in magnetic fields utilizing trapped flux in type-II superconductors

We introduce a novel approach to x-ray scattering studies in applied magnetic fields by exploiting vortices in superconductors. This method is based on trapping magnetic flux in a small disk-shaped superconductor (known as a trapped field magnet, TFM) with a single-crystal sample mounted on or at close proximity to its surface. This opens an unrestricted optical access to the sample and allows magnetic fields to be applied precisely along the x-ray momentum transfer, facilitating polarization-sensitive experiments that have been impractical or impossible to perform to date. The TFMs used in our study remain stable and provide practically uniform magnetic fields for days, which are sufficient for comprehensive x-ray diffraction experiments, specifically x-ray resonance exchange scattering (XRES) to study field-induced phenomena at a modern synchrotron source. The TFM instrument has been used in a "proof-of-principle" XRES study of a meta-magnetic phase in a rare-earth compound, TbNi(2)Ge(2), in order to demonstrate its potential.     

高背景磁场下的差分磁定位算法及应用

为了有效去除高背景磁场对永磁体定位的磁干扰,本文提出了一种高背景磁场下的差分磁定位算法.在背景磁场大小和方向均相等的两位置点处布置一组磁传感器,每组传感器均采用差分放大电路,共八组通路.在高背景磁场下,运用差分磁定位算法反演永磁体的位置和姿态.并将该算法应用于外磁场导向的仿生微型机器人,设计了定位硬件系统.通过实验验证了此差分磁定位算法可以较好地反演该仿生微型机器人位置和姿态.     

A setup for measuring the magnetic characteristics of soft magnetic materials and articles

An automated setup for measuring the normal magnetization curve, the major and minor magnetic-hysteresis loops, and the main (initial permeability, maximum permeability, residual magnetic induction, induction coercive force, and saturation induction) and additional (the permeability at a field equal to the coercive force, the field strength at which the saturation induction is reached, and the induction at fields equal to the coercive force and the double coercive force) magnetic parameters of soft magnetic materials and articles produced from them is described. Measurements are performed in an open or closed magnetic circuit at a magnetization-reversal frequency of 0.05–0.5 Hz. The block diagram of the setup and its main parameters and characteristics are presented. The operation of the setup and the possibilities of its application are considered.     

Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field

We present the design and operation of a fiber-based cryogenic confocal microscope. It is designed as a compact cold-finger that fits inside the bore of a superconducting magnet, and which is a modular unit that can be easily swapped between use in a dilution refrigerator and other cryostats. We aimed at application in quantum optical experiments with electron spins in semiconductors and the design has been optimized for driving with and detection of optical fields with well-defined polarizations. This was implemented with optical access via a polarization maintaining fiber together with Voigt geometry at the cold finger, which circumvents Faraday rotations in the optical components in high magnetic fields. Our unit is versatile for use in experiments that measure photoluminescence, reflection, or transmission, as we demonstrate with a quantum optical experiment with an ensemble of donor-bound electrons in a thin GaAs film.     

用于燃烧场诊断的分子滤波瑞利散射技术

为了测量燃烧场的热力学性质,研究了分子滤波瑞利散射技术.分子滤波瑞利散射技术采用窄线宽激光器、分子滤波器和像增强CCD相机,通过分子吸收凹陷检测激光片照射流场产生散射光的频谱,抑制背景杂散光和米散射,解析流场热力学信息.建立了分子滤波瑞利散射诊断系统和分子滤波器,根据测得的滤波图像和碘蒸气吸收光谱,获得了甲烷一空气预混...     

EPECUR setup for the search for narrow baryon resonances in pion-proton scattering

The EPECUR experimental setup has been designed to search for narrow resonant states by precisely measuring differential and total reaction cross sections for pion-nucleon interactions with 1-MeV pion energy steps. Over the 5 years that passed from the submission of the idea of the experiment to the start of data taking in April 2009, a non-magnetic spectrometer with a liquid hydrogen target based on the large-aperture multiwire drift chambers with a hexagonal structure has been built at the universal beamline 322 of the U-10 proton synchrotron at the Alikhanov Institute for Theoretical and Experimental Physics. Owing to the unique properties of the beamline, the beam particle momentum can be measured with an accuracy of 0.1% or better using 1-mm-pitch proportional chambers located at the first focus of the beamline. The design of numerous subsystems of the setup is based on modern electronic components including microprocessors and field programmable gate arrays. All the subsystems have been tuned and tested both individually and as parts of the whole setup. The distributed data acquisition system is based on the widely spread USB and Ethernet protocols, which help achieve high performance characteristics and take full advantage of the industrial solutions.     

A monitoring and measuring module for tagged neutron experiments

A tagged neutron technology for remote neutron monitoring is used to reduce the background counting rate in recording of useful events. The key elements of the technology are a neutron generator with a built-in α-particle detector, nanosecond electronic system, and fast detectors of secondary radiation produced by emitted neutrons. A module for monitoring and measuring the pulse-height and time parameters of the secondary radiation detector with a time reference to the α-particle detector is described. A prototype of the experimental setup comprising the main components of a standard system based on the tagged neutron technology has been designed to test the module. Numerical calculations have been performed to simulate the γ-ray and neutron transport and the event recording procedure as applied to the geometry of the experimental setup. The time errors and the main sources of background events in measurements using the tagged neutron technology have been investigated. Background counts are shown to affect only slightly the useful data acquired in this geometry.     

ac Modeling and impedance spectrum tests of the superconducting magnetic field coils for the Wendelstein 7-X fusion experiment

The impedance spectrum test was employed for detection of short circuits within Wendelstein 7-X (W7-X) superconducting magnetic field coils. This test is based on measuring the complex impedance over several decades of frequency. The results are compared to predictions of appropriate electrical equivalent circuits of coils in different production states or during cold test. When the equivalent circuit is not too complicated the impedance can be represented by an analytic function. A more detailed analysis is performed with a network simulation code. The overall agreement of measured and calculated or simulated spectra is good. Two types of short circuits which appeared are presented and analyzed. The detection limit of the method is discussed. It is concluded that combined high-voltage ac and low-voltage impedance spectrum tests are ideal means to rule out short circuits in the W7-X coils.     

Experimental setup for lensless imaging via soft x-ray resonant scattering

We have developed a setup for measuring holographically formed interference patterns using an integrated sample-mask design. The direct space image of the sample is obtained via a two-dimensional Fourier transform of the X-ray diffraction pattern. We present the details of our setup, commenting on the influence of geometrical parameters on the imaging capabilities. As an example, we present and discuss the results of test experiments on a patterned Co film.     

A 2D micro-fluxgate earth magnetic field measurement systems with fully automated acquisition setup

In this paper we present an Earth magnetic field measurement system and an automated acquisition setup to characterize it. The measurement system consists of a fluxgate sensor and an integrated front-end circuit, both realized in CMOS technology. The couple of orthogonal axes of the sensor makes the system suitable for realizing an electronic compass device. Indeed, we can measure not only the amplitude of the Earth magnetic field (whose full-scale value is of the order of 60 μT), but also its direction. The complete measurement system achieves a maximum angular error of 1.5° in the measurement of the Earth magnetic field direction. Furthermore, an acquisition setup was developed to evaluate the measurement system performance. It consists of a precision mechanical plastic structure, in tower form, a microcontroller-based interface circuit, that provides a digital output through an RS232 serial interface, a PC software suitably developed to post-process the data from the acquisition system and a couple of Helmholtz coils to evaluate the linearity of the system. This setup allows us to perform a completely automated and numerically controlled characterization of the measurement system.     

A setup with a mechanical chopper for monochromating neutrons and shortening a neutron flux from a pulsed neutron source

A spectrometric setup for studying the resonance structure of the total and partial neutron cross sections at energies below 10 keV has been created. The setup consists of two rotor-type mechanical neutron choppers with dc motors, an electronic system for stabilizing the rotation of rotors and phasing the moment of opening slits along a neutron beam with a neutron pulse, collimators, and neutron detectors. The angular rotational velocity of rotors changes from 0 to 6000 rpm, and their synchronization with the neutron pulse is provided with an accuracy of 10 μs at a minimum time of opening slits along the neutron beam of 20 μs. The setup is transported easily and can be placed on any neutron beam of the ИБР-2 fast pulsed reactor or other neutron sources. The values of the measured basic characteristics of the spectrometer agree with the calculated values within the experimental errors.     

Development of an optimised magnetic field source for flowmeter applications

Sensitivity of a magnetic flowmeter relies on many factors like magnetic field strength, gap between electrodes, material properties, magnet temperature etc. For a given measuring conditions, a strong magnetic field source can produce highest sensitivity for the flowmeter. An economic design of magnetic field source would be to produce the strongest magnetic field from a given amount of magnetic material. In this paper, various magnet configurations are analyzed using FEM and the flowmeter sensitivity using such magnet configurations are compared. It is observed that magnets arranged in a Halbach fashion produce the highest sensitivity for the flowmeter using a given amount of magnetic material. The major challenge for the development of such a magnetic field source is its fabrication from its constituent magnets, combatting their huge attractive/repulsive forces (∼2500 N for our case). Therefore, a specific mechanical tool has been designed for assembling the magnetic field source and a robust assembly technique has been devised using numerical computations. The designed magnetic field source produces a peak magnetic field of 0.78 T in the pole cross section of 50 mm × 50 mm.