Neutron-based characterization techniques for lithium-ion battery research

During the past decades,Li-ion batteries have been one of the most important energy storage devices.Large-scale energy storage requires Li-ion batteries which possess high energy density,low cost,and high safety.Other than advanced battery materials,in-depth understanding of the intrinsic mechanism correlated with cell reaction is also essential for the development of high-performance Li-ion battery.Advanced characterization techniques,especially neutron-based techniques,have greatly promoted Li-ion battery researches.In this review,the characteristics or capabilities of various neutron-based characterization techniques,including elastic neutron scattering,quasi-elastic neutron scattering,neutron imaging,and inelastic neutron scattering,for the related Li-ion-battery researches are summarized.The design of in-situ/operando environment is also discussed.The comprehensive survey on neutron-based characterizations for mechanism understanding will provide guidance for the further study of high-performance Li-ion batteries.

Status of CSNS H-ion source

A new H^- ion source has been installed successfully and will be used to serve the China Spallation Neutron Source （CSNS）. In this paper, we report various components of the ion source, including the discharge chamber, temperature, cooling system, extraction electrodes, analyzing magnet, remote control system and so on. Compared to the previous experimental ion source, some improvements have been made to make the ion source more compact and convenient. In the present arrangement, the Penning field is generated by a pair of pole tip extensions on the 90° analyzing magnet instead of by a separate circuit. For the remote control system, F3RP61-2L is applied to the accelerator online control system for the first time. In the running of the ion source, a stable pulse H^- beam with a current of 50 mA at an energy of 50 keV is produced. The extraction frequency and pulse width is 25 Hz and 500 μs, respectively. Furthermore, an emittance scanner has been installed and measurements are in progress.

Research on radiation dose rate distribution in the backscattering neutron hall of CSNS

Purpose To evaluate the prompt and induced dose rate in backscattering neutron hall for radiation protection and safety management.Method The dose rates were calculated by Monte Carlo code FLUKA,with the"multi-step"simulation method based on traditional"two-step simulation"method.Conclusion Operation time of staff workers does not need to be restricted.But with the increase in beam power and irra-diation time,serious consideration might need to be taken as the dose rate of samples may be higher than the limit value.

Development and prospects of Very Small Angle Neutron Scattering (VSANS) techniques

Very Small Angle Neutron Scattering （VSANS） is an upgrade of the traditional Small Angle Neutron Scattering （SANS） technique which can cover three orders of magnitude of length scale from one nanometer to one micrometer. It is a powerful tool for structure calibration in polymer science, biology, material science and condensed matter physics. Since the first VSANS instrument, Dll in Grenoble, was built in 1972, new collimation techniques, focusing optics （multi-beam converging apertures, material or magnetic lenses, and focusing mirrors） and higher resolution detectors combined with the long flight paths and long incident neutron wavelengths have been developed. In this paper, a detailed review is given of the development, principles and application conditions of various VSANS techniques. Then, beam current gain factors are calculated to evaluate those techniques. A VSANS design for the China Spallation Neutron Source （CSNS） is thereby presented.

Hall sensor angle error and relative position calibrations for cryogenic permanent magnet undulator of high energy photon source test facility(HEPS-TF)

Purpose A new in-vacuum three-dimensional Hall probe magnetic measurement system is under fabrication for characterizing the magnetic performance of the Cryogenic Permanent Magnet Undulator(CPMU).In order to fit the small gap(5 mm)of magnetic structure and vacuum environment,a small three-dimensional Hall probe has been manufactured.The angular and positional misalignment errors of the Hall sensors play an important role in the measurement accuracy of the CPMU.In order to minimize the misalignment errors,a method of calibrating angle error and relative assembly displacements of a three-dimensional Hall probe is carried out.Methods The angle error of Hall sensors will be calibrated by a standard dipole magnet and a five-dimensional Hall bench.The standard dipole magnet will generate a single direction and uniform magnetic field.And the fivedimensional Hall bench is used to rotate the Hall probe which is put in the center of magnet.Based on the relationship between angle and magnetic field strength,the angle error of each Hall sensor will be obtained.The relative position between the sensitive areas of the Hall sensors will be calibrated by a two-dimensional magnetic field undulator section.Based on Maxwell’s equations,through the calculation of measurement magnetic field strength,the relative assembly displacements of the three Hall sensors can be derived.Results The details of the calibration methods and the data processing of angle error and relative assembly displacements of a three-dimensional Hall probe are presented.The three-dimensional magnetic fields of a cryogenic permanent magnet undulator can be received accurately by correcting these angle errors and position errors of Hall sensors.Conclusions This paper illustrates the relative position and angle calibration procedures and the data processing of a three-dimensional Hall probe.Now the design of a smaller Hall probe is in process.The calibration of the angle errors and position errors will be carried out after the fabrication of the standard dipole magnet.

The operation and improvement of CSNS front end

Introduction Operation target beam power of China Spallation Neutron Source(CSNS),as the China's first 100 kW beam power pulsed neutron source,is now larger than 80 kW.During the beam power upgrading process of CSNS to 50 kW from 2018 to 2019,many improvements have been made for the front end of CSNS.Results The improvements mainly focus on solving the problems of ion source instability and the radio frequency quadrupole(RFQ)sparking caused by the pre-chopped beam into RFQ.

Analysis and experimental concepts of the vibrating wire alignment technique

The vibrating wire alignment technique is a method which, by measuring the spatial distribution of a magnetic field, can achieve very high alignment accuracy. The vibrating wire alignment technique can be applied to fiducializing magnets and the alignment of accelerator straight section components, and it is a necessary supplement to conventional alignment methods. This article gives a systematic summary of the vibrating wire alignment technique, including vibrating wire model analysis, system frequency calculation, wire sag calculation, and the relation between wire amplitude and magnetic induction intensity. On the basis of this analysis, this article outlines two existing alignment methods, one based on magnetic field measurement and the other on amplitude and phase measurements. Finally, some basic experimental issues are discussed.

Morphology Evolution of Polystyrene-core/Poly(N-isopropylacrylamide)-shell Microgel Synthesized by One-pot Polymerization

One-pot polymerization with macroinitiator is supposed to be a robust, facile way to synthesize well-defined core- shell nanoparticles with fixed shell thickness. To testify this, we investigated the temperature-depending morphology evolution of polystyrene （PS） core/poly（N-isopropylacrylamide） （PNIPAM） shell microgel synthesized by one-pot polymerization with PNIPAM-RAFT as macroinitiator in dimethylformamide （DMF） by transmission electron microscopy （TEM）, dynamic/static light scattering （DLS/SLS） and small angle neutron scattering （SANS）. It is revealed that the microgel has a core-shell structure, i.e., the core is made of pure PS, but the shell is composed of both PNIPAM-RAFT macroinitiator and crosslinked PS. In fact, there are 92.0 wt% D20, 6.7 wt% PNIPAM and 1.3 wt% PS in the shell in its aqueous dispersion at 21 ℃; therefore, its shell thickness is much larger than the extended chain length of the macroinitiator as revealed by both SANS and DLS observations. Competitive growth of styrene, divinylbenzene and PNIPAM macroinitiator as well as possible chain transfer from amine proton of PNIPAM side chain may lead to the larger shell thickness, compared with the extended chain length of the macroinitiator. Our work can shed light on the real morphology control in one-pot polymerization.

Magnetic field strength and temperature-dependent calibration system of Hall probe for the HEPS-TF cryogenic permanent magnet undulator

Purpose High energy photon source test facility(HEPS-TF)has manufactured a three-dimensional Hall probe to measure the cryogenic permanent magnet undulator(CPMU).Since the operating environment of the CPMU is the subcooled liquid nitrogen(85K),the temperature of the Hall probe will have a decrease of several degrees while carrying out the local magnetic measurement.We established a magnetic field strength and temperature-dependent calibration system to calibrate the Hall probe.Methods The magnetic field strength of the Hall probe was calibrated by a standard dipole electromagnet and a nuclear magnetic resonance Tesla meter(NMR).The temperature of Hall probe was controlled by a control system which can modulate temperature from 0℃ to 30℃.Results A new homemade Hall probe has finished the temperature-dependent(0℃ to 30℃),magnetic field strength(-1.2 to 1.2 T)and angle error calibration at this new calibration system.The temperature correction error is less than 0.045%.The calibration error of magnetic field strength is less than 1.5 Gs.The RMS calibration error of Hall sensors angle matrix is less than 5.1E-5.Conclusion The magnetic field strength and temperature-dependent calibration system including a standard dipole electromagnet,a temperature regulation system,an NMR and a five-dimensional Hall bench was established.The detailed magnetic field strength and temperature-dependent calibration system is introduced and the results of the calibrations are presented.