Millisecond dynamics of colloidal suspension studied by X-ray photon correlation spectroscopy at the Shanghai Synchrotron Radiation Facility

X-ray photon correlation spectroscopy(XPCS)has emerged as a powerful tool for probing the nanoscale dynamics of soft condensed matter and strongly correlated materials owing to its high spatial resolution and penetration capabilities.This technique requires high brilliance and beam coherence,which are not directly available at modern synchrotron beamlines in China.To facilitate future XPCS experiments,we modified the optical setup of the newly commissioned BL10U1 USAXS beamline at the Shanghai Synchrotron Radiation Facility(SSRF).Subsequently,we performed XPCS measurements on silica suspensions in glycerol,which were opaque owing to their high concentrations.Images were collected using a high frame rate area detector.A comprehensive analysis was performed,yielding correlation functions and several key dynamic parameters.All the results were consistent with the theory of Brownian motion and demonstrated the feasibility of XPCS at SSRF.Finally,by carefully optimizing the setup and analyzing the algorithms,we achieved a time resolution of 2 ms,which enabled the characterization of millisecond dynamics in opaque systems.

Development of a three dimension multi-physics code for molten salt fast reactor

Molten Salt Reactor(MSR) was selected as one of the six innovative nuclear reactors by the Generation IV International Forum(GIF).The circulating-fuel in the can-type molten salt fast reactor makes the neutronics and thermo-hydraulics of the reactor strongly coupled and different from that of traditional solid-fuel reactors.In the present paper,a new coupling model is presented that physically describes the inherent relations between the neutron flux,the delayed neutron precursor,the heat transfer and the turbulent flow.Based on the model,integrating nuclear data processing,CAD modeling,structured and unstructured mesh technology,data analysis and visualization application,a three dimension steady state simulation code system(MSR3DS) for the can-type molten salt fast reactor is developed and validated.In order to demonstrate the ability of the code,the three dimension distributions of the velocity,the neutron flux,the delayed neutron precursor and the temperature were obtained for the simplified MOlten Salt Advanced Reactor Transmuter(MOSART) using this code.The results indicate that the MSR3DS code can provide a feasible description of multi-physical coupling phenomena in can-type molten salt fast reactor.Furthermore,the code can well predict the flow effect of fuel salt and the transport effect of the turbulent diffusion.

Design of wide-range energy material beamline at the Shanghai Synchrotron Radiation Facility

We report the design of a wide-range energy material beamline(E-line) with multiple experimental techniques at the Shanghai Synchrotron Radiation Facility.The undulators consisted of an elliptically polarizing undulator and in-vacuum undulator that generate the soft and hard X-rays, respectively. The beamline covered a wide energy range from 130 to 18 ke V with both a high photon flux([ 10^(12) phs/s with exit silt 30 lm in soft X-ray and [ 5 9 10^(12) phs/s in hard X-ray within 0.1%BW bandwidth) and promising resolving power(maximum E/DE [ 15,000 in soft X-ray with exit silt 30 lm and [6000 in hard X-ray). Moreover, the beam spots from the soft and hard X-rays were focused to the same sample position with a high overlap ratio, so that the surfaces, interfaces, and bulk properties were characterized in situ by changing the probing depth.

Simulation study of slow extraction for the Shanghai Advanced Proton Therapy facility

The Shanghai Advanced Proton Therapy facility employs third-integer slow extraction. In order to achieve accurate treatment, high-quality spill is needed. Therefore,parameters that may affect slow extraction should be investigated by simulation. A computer model of the synchrotron operation slow extraction was constructed with MATLAB~. By simulating the motion of the circulating protons, we could quantify the influence of machine and initial beam parameters on properties of the extracted beam, such as ripple, uniformity, stability, on-and off-time of the spill and spill width in the synchrotron.Suitable design parameters including the horizontal tunes,power supply ripple, longitudinal RF cavity voltage, RFKO and the chromaticities were determined.

Tuning control system of a third harmonic superconducting cavity in the Shanghai Synchrotron Radiation Facility

Beam lifetime is dominated by Touschek scattering at the Shanghai Synchrotron Radiation Facility(SSRF).Touschek loss rate is affected by probability for scattering beyond the RF acceptance and the volume charge density of the bench.In the phaseⅡupgrade of the SSRF,a third harmonic superconducting cavity will be used to enhance the Touschek lifetime by lengthening the bunches.The Touschek lifetime improvement factor is affected by the voltage of a harmonic cavity.To stabilize the cavity voltage,a tuning control system was designed to control it.The design of the tuning control system was based on the SSRF third-generation low-level RF control system.Some hardware and specialized algorithms were redesigned to fit the harmonic cavity control.The design of the tuning control system is complete,and the control system has been tested.The test result shows that the fluctuation of amplitude is<±0.34%within 1.5 h,which satisfies the stability requirement.

Generation of double pulses at the Shanghai soft X-ray free electron laser facility

In this article, we present the promise of a new method generating double electron pulses in picosecondscale pulse length and tunable interpulse spacing at several picoseconds. This has witnessed an impressive potential of application in pump–probe techniques, two-color X-ray free electron laser, high-gradient witness bunch acceleration in a plasma, etc. Three-dimensional simulations are carried out to analyze the dynamic of the electron beam in a linear accelerator. Comparisons are made between the new method and existing ways.

Optimization of the cavity beam-position monitor system for the Shanghai soft X-ray free-electron laser user facility

To achieve high-efficiency operation of the highgain free-electron laser(FEL),the electron beams and radiated photon beams need to be overlapped precisely and pass through the entire undulator section.Therefore,a high-resolution beam-position monitor(BPM)is required.A cavity BPM(CBPM)with a resonant cavity structure was developed and used in the Shanghai Soft X-ray FEL(SXFEL)test facility and can achieve a position resolution of<1μm.The construction and operation of the SXFEL user facility also bring about higher requirements for beamposition measurement.In this case,the factors that affect the performance of the CBPM system were further analyzed.These included the amplitude and phase stability of the local oscillator,stability of the trigger signal,performance of the radio frequency front-end,signal processing electronics,and signal processing algorithms.Based on the upgrade and optimization of the system,a beam test platform was built at the end of the linear acceleration section of the SXFEL,and the experimental results show that the position resolution of the system can reach 177 nm at a bunch charge of 500 pC,and the dynamic range is controlled within±300μm,and the relative measurement uncertainty of the bunch charge can reach 0.021%,which are significant improvements compared to the attributes of the previous system.

Large eddy simulation of unsteady flow in gas-liquid separator applied in thorium molten salt reactor

Axial gas-liquid separators have been adopted in fission gas removal systems for the development of thorium molten salt reactors. In our previous study, we observed an unsteady flow phenomenon in which the flow pattern is directly dependent on the backpressure in a gas-liquid separator; however, the underlying flow mechanism is still unknown. In order to move a step further in clarifying how the flow pattern evolves with a variation in backpressure, a large eddy simulation(LES) was adopted to study the flow field evolution. In the simulation, an artificial boundary was applied at the separator outlet under the assumption that the backpressure increases linearly. The numerical results indicate that the unsteady flow feature is captured by the LES approach, and the flow transition is mainly due to the axial velocity profile redistribution induced by the backpressure variation. With the increase in backpressure,the axial velocity near the downstream orifice transits from negative to positive. This change in the axial velocity sign forces the unstable spiral vortex to become a stable rectilinear vortex.

Dual-cavity beam arrival time monitor design for the Shanghai soft X-ray FEL facility

Free electron lasers provide high-power and ultrashort pulses with extreme brightness. In order to improve a facility's capabilities and explore the possibility of performing high-resolution time-resolved experiments, a beam arrival time resolution under 100 fs is required. In this article, a novel beam arrival time monitor(BAM)equipped with two cavities has been designed and a beam flight time measurement scheme based on the BAM prototype has been proposed to estimate phase jitter in the signal measurement system. The two BAM cavities work at different frequencies and the frequency difference is designed to be 35 MHz. Therefore, a self-mixing intermediate frequency signal can be generated using the two cavities. The measured beam flight time shows a temporal deviation of 37 fs(rms).

Transverse phase space reconstruction study in Shanghai soft X-ray FEL facility

Phase space is one of the most important parameters used to describe beam properties. Computer tomography, as a method for reconstructing phase space and measuring beam emittance, has been used in many accelerators over the past few decades. In this paper, we demonstrate a transverse phase space reconstruction study in the Shanghai soft X-ray free electron laser facility. First,we discuss the basic principles of phase space reconstruction and the advantage of reconstructing beam distribution in normalized phase space. Then, the phase space reconstruction results by different computer tomography methods based on the maximum entropy(MENT) algorithm and the filtered back projection algorithm in normalized phase space are presented. The simulation results indicate that,with proper configuration of the phase advance between adjacent screens, the MENT algorithm is feasible and has good efficiency. The beam emittance and Twiss parameters are also calculated using the reconstructed phase space.

Gantry optimization of the Shanghai Advanced Proton Therapy facility

A proton therapy system is a large medical device to treat tumors.Its gantry is of large structure and high precision.A new half-gantry was designed in the Shanghai Advanced Proton Therapy(SAPT)project.In this paper,the weight of gantry in design is reduced significantly by size and structure optimizations,to improve its cost-effectiveness,while guaranteeing the functions and precision.The processes of physics optimization,empirical design optimization,topological optimization and size optimization,together with factors of consideration,are described.The gantry weight is reduced by 30%,with the same precision.

Neutronics physics analysis of a large fluoride-salt-cooled solidfuel fast reactor with Th-based fuel

Fast reactors based on thorium fuel have enhanced inherent safety. Fluoride salt performs well as a coolant in high-temperature nuclear systems. In this paper,we present a reference core for a large fluoride-salt-cooled solid-fuel fast reactor(LSFR) using thorium–uranium fuel cycle. Neutronics physics of the LSFR reference core is investigated with 2D and 3D in-core fuel management strategy. The design parameters analyzed include the fuel volume fraction, power density level and continuous removal of fission products with 3D fuel shuffling that obtains better equilibrium core performance than 2D shuffling. A self-sustained core is achieved for all cases,and the core of 60% fuel volume fraction at 50 MW/m^3 power density is of the best breeding performance(average breeding ratio 1.134). The LSFR core based on thorium fuel is advantageous in its high discharge burn-up of 20–30% fissions per initial heavy metal atom, small reactivity swing over the whole lifetime(to simplify the reactivity control system), the negative reactivity temperature coefficient(intrinsically safe for all cases) and accepted cladding peak radiation damage. The LSFR reactor is a good alternative option for the deployment of a self-sustained thorium-based nuclear system.

Physics performance of the STAR zero degree calorimeter at relativistic heavy ion collider

The zero degree calorimeter(ZDC) at RHICSTAR was installed in the year 2000.After running for more than 10 years,the performance of the STAR-ZDC cannot maintain a proper status because of the radiation damage.The ZDC on RHIC-BRAHMS had been moved to STAR in 2011 after some tests.We present here the result of the tests as well as the physical performance of those ZDC modules between the 2011 and 2015 RHIC runs.The excellent energy resolution of the ZDC in heavy ion collision provides a good candidate for future detector development,such as the CSR experiment at CAS-Lanzhou facility.

Dynamic simulation analysis of molten salt reactor-coupled air-steam combined cycle power generation system

A nonlinear dynamic simulation model based on coordinated control of speed and flow rate for the molten salt reactor and combined cycle systems is proposed here to ensure the coordination and stability between the molten salt reactor and power system.This model considers the impact of thermal properties of fluid variation on accuracy and has been validated with Simulink.This study reveals the capability of the control system to compensate for anomalous situations and maintain shaft stability in the event of perturbations occurring in high-temperature molten salt tank outlet parameters.Meanwhile,the control system’s impact on the system’s dynamic characteristics under molten salt disturbance is also analyzed.The results reveal that after the disturbance occurs,the controlled system benefits from the action of the control,and the overshoot and disturbance amplitude are positively correlated,while the system power and frequency eventually return to the initial values.This simulation model provides a basis for utilizing molten salt reactors for power generation and maintaining grid stability.

Review on synergistic damage effect of irradiation and corrosion on reactor structural alloys

The synergistic damage effect of irradiation and corrosion of reactor structural materials has been a prominent research focus.This paper provides a comprehensive review of the synergistic effects on the third-and fourth-generation fission nuclear energy structural materials used in pressurized water reactors and molten salt reactors.The competitive mechanisms of multiple influencing factors,such as the irradiation dose,corrosion type,and environmental temperature,are summarized in this paper.Conceptual approaches are proposed to alleviate the synergistic damage caused by irradiation and corrosion,thereby promoting in-depth research in the future and solving this key challenge for the structural materials used in reactors.

Corrosion behavior of pure metals(Ni and Ti)and alloys(316H SS and GH3535)in liquid GaInSn

In this study,the interactions between a Ga-based liquid metal,GaInSn,and several metal materials,including pure metals(Ni and Ti)and alloys(316H stainless steel(SS)and GH3535),at 650℃were investigated.The aim was to evaluate the corrosion performance and select a suitable candidate material for use as a molten salt manometer diaphragm in thermal energy storage systems.The results indicated that the alloys(316H SS and GH3535)exhibited less corrosion than pure metals(Ni and Ti)in liquid GaInSn.Ga-rich binary intermetallic compounds were found to form on the surfaces of all the tested metal materials exposed to liquid GaInSn,as a result of the decomposition of liquid GaInSn and its reaction with the constituent elements of the metal materials.The corrosion mechanism for all the tested materials exposed to liquid GaInSn was also investigated and proposed,which may aid in selecting the optimal candidate material when liquid GaInSn is used as the pressure-sensing medium.

A modeling GUI for accelerator physics of the storage ring at SSRF

In this paper,we report a MATLAB-based GUI tool,bodgui,which integrates functions of lattice editor,linear match,and nonlinear optimization,and visualized tracking functions for beam optics design.A user can switch his/her design procedures one to another.Flexibilities are provided for adjusting or optimizing the lattice settings in commissioning or operation of the accelerators.The algorithm of the linear match and nonlinear optimization,and the GUI windows including the main functions and running status,are presented.The SSRF storage ring was employed as a test lattice.Several optics modes designed and optimized by the GUI tools were used for commissioning the storage ring.Functions of bodgui tool are machine-independent,and it can be well applied to modern light sources being built in other parts of the world.

The front-end electronics design of dose monitors for beam delivery system of Shanghai Advanced Proton Therapy Facility

A front-end electronics of dose monitor has been developed for measuring irradiation dose to the patient in Shanghai Advanced Proton Therapy Facility.The parallel plate ionization chamber is used for the dose monitoring.Unlike the traditional method of recycling capacitor integration and voltage-to-frequency conversion,this dose monitor electronics uses the trans-impedance amplifier and analog-to-digital conversion method.It performs satisfactorily,with the integral nonlinearity of less than ±0.04 nA in the range of-400 to 50 nA and the resolution of about±0.6 nA.

An S-band solid-state radio frequency power amplifier used at Shanghai soft X-ray FEL facility

In this paper,we present the general design methods and parameter measurements of a 1-k W solidstate radio frequency(RF) power amplifier at 2856 MHz,for the soft X-ray free electron laser facility.Three-stage amplification with a 4-way combination is used.An RF switch module is integrated with the solid-state RF power amplifier to convert the continuous wave(CW) signal into pulse signal,with adjustable pulse width.The power gain is measured at 57.7 d B at 60 d Bm output.The RF phase noise,which is measured by the low-level RF system,is\0.015 degree(RMS),while the pulse frontier jitter is\5 ns.

On harmonic operation of Shanghai deep UV free electron laser

By choosing parameters in the modulator, the dispersive section and the seed laser, the spatial bunching of the electron beam can be correlated to the n-th harmonic of the radiator radiation, instead of the fundamental radiation in conventional high-gain harmonic generation (HGHG). Thus, the radiator undulator is operated at high harmonic mode. In this paper, the possibility of harmonic operation of Shanghai deep ultraviolet (SDUV) free electron laser (FEL) is studied. Discussions on the principle of harmonic operation, the simulation code development, the simulation results, and the proposed experimental procedure for verification of harmonic operation at the SDUV FEL are also presented.