Light Facility Research Articles

Performance Parameters and Stability Studies on FEL-III Beamline of Shanghai High Repetition Rate XFEL and Extreme Light Facility

Performance Parameters and Stability Studies on FEL-III Beamline of Shanghai High Repetition Rate XFEL and Extreme Light Facility

Simulation of wire scanner for high repetition free electron laser facilities

The high-gain Free Electron Lasers (FEL) have promised scientists for new scientific discoveries in many frontier research areas. For that purpose, this kind of facilities have been installed or will be installed worldwide. As to FELs, high repetition is the future development trend. Herein, wire scanner provides a measurement of beam profile which realizes real-time and non-intercepting for the FELs. The simulation of key parameters of wire scanner for the FELs is discussed in this paper. Since wire scanner for FELs mainly use tungsten wires, then empirical formula for optimum installation position of Beam Loss Monitor (BLM) and empirical formula for the maximum temperature of tungsten wires are given based on theoretical analysis and numerical simulation. These formulas can provide a reference for high repetition and high-gain FELs that will be installed with wire scanners in the future. In recent years, the Shanghai HIgh repetition rate XFEL aNd Extreme light facility (SHINE), a quasi-continuous wave hard X-ray free electron laser facility, is under construction in China. Upon its completion, the linear accelerator will accelerate electrons with bunch charge of 10–300 pC to 8 GeV, at a maximum repetition frequency of 1 MHz. We calculate key parameters of the wire scanner for SHINE with these empirical formulas.

Possibility of simulating natural circulation in fast neutron reactors using a light water test facility

The paper evaluates the possibility of modeling the heat transfer phenomena in a liquid-metal coolant using a light water test facility. It considers the natural circulation of the coolant in the upper plenum of the fast-neutron reactor. The sodium-cooled BN-1200 reactor was selected as the reactor installation to be modeled. The development of novel reactor designs must be based on the results of experimental studies. Some problems of modeling thermohydraulic processes in BN type reactors are studied by using sodium test facilities. Experimental studies of natural convection processes using light water test facilities can be considered as a good alternative to those using sodium test facilities. To validate the model, the similarity theory and the “black box” method were used and their principles and applicability were analyzed. Using the “black box” method makes it possible to avoid detailed modeling of such components as the reactor core and heat exchangers, replacing them by a simplified representation of these components to simulate the integral characteristics of the existing real life equipment. The paper considers the basic criteria which determine the similarity of the thermohydraulic processes under study. The governing criteria of similarity were estimated based on the fundamental differential equations of natural convection heat transfer. Based on these criteria, a set of dimensionless values was obtained which show the correlation between the model parameters and the characteristics of the reactor facility. Besides, generalized relationships were derived which can be used to estimate the scaling factors for calculating the key values of the reactor facility based on the model parameters. These relationships depend on the thermal-physics parameters of the working fluids, the geometrical scale value and the ratio of the thermal power of the model to that of the reactor facility, i.e., model-to-reactor thermal power ratio. The conditions under which it is possible to model sodium coolant by light water with adequate accuracy were analyzed. An example is given of the numerical values of the scaling factors for one of the reference light water test facilities. The paper uses the experience of a number of foreign researchers in this field, in particular, the accepted assumptions which do not result in serious loss in modeling accuracy. According to the available estimates, the assumptions used do not result in considerable losses in accuracy. Thus, the natural circulation of the sodium coolant in the upper plenum of the fast-neutron reactor can be simulated with adequate accuracy by using light water test facilities.

Inhibition of current-spike formation based on longitudinal phase space manipulation for high-repetition-rate X-ray FEL

The formation of a double-horn current profile is a challenging issue in the achievement of electron bunch with high peak current, especially for high-repetition-rate X-ray free-electron lasers (XFELs) where more nonlinear and intricate beam dynamics propagation is involved. Here, we propose to correct the nonlinear beam longitudinal phase space distortion in the photoinjector section with a dual-mode buncher. In combination with the evolutionary many-objective beam dynamics optimization, this method is shown to be effective in manipulating the longitudinal phase space at the injector exit. Furthermore, the formation of the current spike is avoided after the multi-stage charge density modulation and electron bunch with a peak current of 1.6 kA is achieved for 100-pC bunch charge. Start-to-end simulations based on the Shanghai high-repetition-rate XFEL and extreme light facility demonstrate that the proposed scheme can increase the FEL pulse energy by more than 3 times in a cascading operation of echo-enabled harmonic generation and high-gain harmonic generation. Moreover, this method can also be used for longitudinal phase space shaping of electron beams operating at a high repetition rate to meet the specific demands of different researches.

Experimental investigation of large-scale high-velocity soft-body impact on composite laminates

High-performance aerospace laminated composite structures manufactured from carbon-fibre prepreg are very susceptible to delamination failure under in-flight impact conditions. Much testing has been conducted at small length scales and quasi-static strain-rates to characterise the delamination performance of different material systems and loading scenarios. Testing at this scale and strain-rate is not representative of the failure conditions experienced by a laminate in a real impact event. Full-scale testing has also been conducted, but much of this is not in the open literature due to intellectual property constraints. Testing at this scale is also prohibitively expensive and involves complex failure mechanisms that cause difficulty in the analysis of associated failure behaviour. A novel test is presented which provides a simple, affordable alternative to full-scale testing but which invokes failure at sufficient scale and velocity to be representative of real component failure. This test design is experimentally validated through a series of soft-body gelatine impact tests using a light gas-gun facility. A fractographic analysis using scanning-electron microscopy was undertaken to examine microscopic failure behaviour, showing a possible reduction in crack mode-ratio during propagation.

Research on vacuum properties of CuCrZr UHV flanges for the Hefei Advanced Light Facility

Hefei Advanced Light Facility (HALF), one of the Diffraction-Limited Storage Rings (DLSR), requires low-impedance flanges to be welded with Oxygen-free with Ag (OFS) vacuum chamber. In this paper, CuCrZr alloy as flange material and spring energized metal C-ring sealing structure are proposed. Two types of CuCrZr flanges have been designed, which are chain clamp and bolted flange, respectively. Chain clamp flanges are planed for compact areas, due to its small axial dimension. Bolted flanges with better positioning ability are designed to place in sections without space limitation. A series of leak rate and outgassing rate measurements were performed, and force and finite element analyses were carried out. Leak rates of both two flanges are lower than 5×10−13Pam3s−1 after 10 times seal-changing tests and 15 times same-seal bakeout cycles. Required fastening torques of chain clamp and bolted flange are 5–7 N m and 3–5 N m, respectively, in order to achieve sealing. The outgassing rate of CuCrZr is about an order of magnitude less than that of stainless steel after bakeout to 250 °C. The simulation results indicate that stress on the CuCrZr flange is far lower than metal C-ring due to the large deformation of the seal.

Graphics-processing-unit-accelerated simulation for longitudinal beam dynamics of arbitrary bunch trains in electron storage rings

We propose a novel algorithm to deal with the interaction of beam-cavity, which is convenient to be implemented on the platform of matlab supporting graphics process unit operations and can significantly improve the computational efficiency. Actually, this algorithm has been implemented and the corresponding code is named stable, which can be used to study the longitudinal beam dynamics of arbitrary filled bunches in electron storage rings. In this paper, the stable code is mainly used to evaluate the bunch lengthening produced by the passive higher harmonic cavity. We first carry out efficiency tests for stable and the results are satisfactory. We then benchmark the stable code against the semianalytical approach and elegant tracking for equilibrium and nonequilibrium cases, respectively, and the results are in good agreement. Furthermore, the stable code is applied to the case of Advanced Light Source upgrade (ALS-U) with distributed gaps, and the results firstly reveal a regular and periodic transient beam loading effect and thus show a nonequilibrium state for the overstretching case. As a second example, the stable code is also applied to the case of the Hefei advanced light facility (HALF) storage ring with uniformly distributed gaps, and the results show that the passive normal conducting harmonic cavities with a total $R/Q$ of $\ensuremath{\sim}200\text{ }\text{ }\mathrm{\ensuremath{\Omega}}$ will cause severe transient effects, thus being not suitable for Hefei advanced light facility.

Micro telecom computing architecture.4-based beam position monitor electronics design for storage ring of Hefei advanced light facility.

The Hefei Advanced Light Facility (HALF) is a fourth-generation vacuum ultraviolet and x-ray diffraction limit synchrotron radiation (DLSR) light source now under preliminary research. To achieve ultralow beam emittance and small beam size, the orbit of the beam in the DLSR storage ring should meet the stability requirement at submicrometer scale. The beam position monitor (BPM) electronics measures the orbit and is hence an essential part of the beam orbit control system. In this article, we designa BPM electronics based on the MicroTCA.4 (Micro Telecom Computing Architecture) standards platform, which consists of a MicroTCA.4 module (including a chassis, a power supply, and a digital board), a customized RF front end module, and a frequency synthesizer. In-phase and quadrature sampling and digital signal processing algorithms are implemented to obtain turn-by-turn data, fast acquisition data at a 10 kHz rate, and slow acquisition data at a 10Hz rate. To evaluate the performance and function of BPM electronics, we conducted offline tests in the laboratory and beam tests based on the storage ring of Hefei Light Source II (HLS II), a light source similar to the HALF as an alternative. Test results indicate that the performance of MicroTCA.4-based BPM electronics can meet the requirements of the HALF storage ring.

Ensuring radiation safety during temporary storage of solidified radioactive waste in light hangar-type facilities

Expensive permanent storage facilities with massive engineered structures are used traditionally to ensure safe temporary storage of solidified radioactive waste at the NPP sites. Such approach is dictated by the need to comply with the regulatory requirements for limiting the gamma background in the area adjacent to the storage facility. The costs involved in temporary storage of solidified RW can be optimized by using light hangar-type storage facilities. At the same time, the safety of storage, including radiation protection of the personnel, the public and the environment, is undoubtedly ensured through the use of special organizational and engineering solutions. The Novovoronezh NPP, a branch of JSC Concern Rosenergoatom, operates successfully light hangar-type facilities for temporary storage of solidified RW classified as medium-level waste in accordance with OSPORB-99/2009. In the process of operation, a methodology and a method for conditioning and temporary storage of solidified RW were developed to ensure the RW removal for final disposal with no extra process operations and unreasonable costs. A methodology has been developed to assess the radiation situation around storage facilities during temporary storage of RW, as well as a software package for predicting the radiation situation when deciding on the arrangement of the storage facility’s peripheral rows.

The first infrared beamline at the Middle East SESAME synchrotron facility

SESAME (Synchrotron-light for Experimental Science and Applications in theMiddle East) is the only synchrotron light facility in the Middle East and neighboring regions, officially opened in 2017. Among the identification and construction of the first operational beamlines, infrared spectromicroscopy was selected as one of the two beamlines to be opened to the general users' program (the so-called Day-1 beamlines). Being one of the most demanded techniques by various scientific communities in the Middle East, the beamline has been designed and implemented in the framework of a collaboration agreement with the French synchrotron facility, SOLEIL. The design, construction and initial performances of the IR beamline (D02-IR), nowadays operational, are reported.

Prototype of Clock and Timing Distribution and Synchronization Electronics for SHINE

Shanghai high repetition rate X-ray-free electron laser (XFEL) and extreme light facility (SHINE) has been under construction. It aims at producing X-ray pulses in a photon energy range from 0.4 to 25 keV. To achieve the design goal, SHINE requires precise distribution and synchronization of the clock and timing signals over a long distance of approximately 3.1 km. Based on the standard White Rabbit (WR) protocol, a prototype of a high-precision clock and timing electronics is designed based on a customized clock frequency. Great attention is paid to the design of hardware and field programmable gate array (FPGA) logic to achieve high-precision clock synchronization, fine phase adjustment, and frequency tuning, as well as flexible shaping of timing signals. Test results indicate that the skew jitter of the clock signal is better than 20 ps within the frequency range from around 1 Hz to 1 MHz, and the clock phase delay can be adjusted with a step size of about 500 ps. As for the timing signals, the skew jitter is better than 40 ps rms. Moreover, the temperature drifts of the clock and timing signals are better than 3 ps/°C.

Development of a high-power EUV irradiation tool in a hydrogen atmosphere

Extreme ultraviolet (EUV) lithography has recently been utilized as a high-volume manufacturing technology for advanced semiconductors. An EUV mirror can be easily contaminated in the existence of a residual hydrocarbon vapor gas inside an exposure chamber in a vacuum environment, which reduces the reflectance of the Mo/Si multilayer coating. To reduce this carbon contamination, hydrogen gas is introduced at a pressure of a few pascals in the EUV scanner. However, during this process, the multilayer may be damaged by hydrogen. In addition, the multilayer surface can become oxidized by residual water vapor in the vacuum chamber. Therefore, an EUV irradiation tool in hydrogen and water vapor atmospheres was developed and installed at BL-09 of the NewSUBARU synchrotron light facility to evaluate the cleaning effect and irradiation durability of the Mo/Si multilayer. The EUV irradiation intensity increased up to 6 W cm−2, and the hydrogen pressure reached 70 Pa.

Development of a High-Resolution Digital Beam Position Processor for the Hefei Advanced Light Facility Preresearch Project

A digital beam position processor (DBPP) with high resolution is required and developed for the Hefei Advanced Light Facility Preresearch Project to measure the orbit information and control the beam orbit jitter within one-tenth of the beam size. In this article, the design of the developed processor is presented in detail. Special attention is given to the analog part of the processor for a small noise figure and the calibration method for acceptable long-term stability. Different from the traditional calibration method using only the quasi-crossbar switch, our method combines temperature compensation attenuators, static digital attenuators, and the quasi-crossbar switch to a compound dynamic calibration method. In addition, a design of a switchable amplification stage is adopted to reduce the noise figure. A test stand, specially designed for the calibration and tests of the processor, is described. The initial laboratory tests show that the DBPP has a resolution of ~500 nm for turn-by-turn position, ~90 nm for fast acquisition at 5.03 kS/s rate, and ~30 nm for slow acquisition at 9.83-S/s rate, at a simulated beam current of about 500 mA. The alternative tests of the processor at Hefei light source-II verify the performance.

The cryogenic control system of SHINE

The Shanghai High repetition rate XFEL and Extreme Light Facility (SHINE), an advanced XFEL project, is now being built at Shanghai Advanced Research Institute (SARI), Chinese Academy of Sciences. It includes a hard X-ray free electron laser and a 100 pW intense laser facilities with overall length of 3.1 km. The XFEL part including an 8 GeV LINAC and 3 undulator lines is cooled with forced superfluid and supercritical helium at 2 K/4 K. The cryogenic system of SHINE consists of test facility cryogenic system (TFCS), accelerator cryogenic system (ACCS), and undulator cryogenic system (UNCS). A dedicated control system based on Experimental Physics and Industrial Control System (EPICS) will be built to automate the cryogenic system with process control, PID control loops, real-time data acquisition and storage, alarm handler and human machine interface. It is capable of automatic recovery as well. This paper describes details of control system structure, interfaces, controllers and the integration under EPICS framework.

Conceptual design and theoretical analysis of a system: The reference network of alignment

As a fourth-generation light source based on a diffraction-limited storage ring, Hefei Advanced Light Facility (HALF) has higher requirements for the alignment of magnets in terms of accuracy, efficiency and reliability. In this paper, we propose a system called the Reference Network of Alignment (RNA) that can achieve a transverse alignment accuracy of the magnets of ±20μm along a 100 m straight section of the accelerator. We first present the concept underlying the design of the RNA system. The girder assembly on which several common axis magnets are fixed forms the independent unit, and a long stretched wire is used as a straightness reference. A theoretical analysis of our system is then presented based on strict mathematical models that center on the combining method of the wire position sensors, the hydrostatic leveling sensors, and two-axis inclination sensors, for which the positions and orientations are known relative to each other. Finally, we perform a simulation of the RNA system using the Monte Carlo method. The results show that it is credible to assume that the RNA system can achieve an alignment installation accuracy of 20 μm and a displacement monitoring accuracy of 15 μm.

Fundamental Evaluation of Resist on EUV Lithography at NewSUBARU Synchrotron Light Facility

Fundamental Evaluation of Resist on EUV Lithography at NewSUBARU Synchrotron Light Facility

Thermal analysis for fundamental power coupler of HALF 499.8 MHz superconducting cavity

The preliminary research work of Hefei Advanced Light Facility (HALF), a fourth generation diffraction limit storage ring, is in progress. Two 499.8 MHz superconducting cavities may be used in the HALF RF system. RF power will be feed into each cavity through a coaxial fundamental power coupler (FPC). Thermal design of the coupler is very important because of the large power losses on the coupler will cause overheating. Accurate and fast thermal analysis is a challenge in the thermal design. In this paper, two thermal analysis methods for evaluating the cooling effect of the coupler were compared. Computational Fluid Dynamics (CFD) code is used to perform thermal-fluid coupled analysis for the coupler in the first method, which is quite accurate but time-consuming. In the second method, average convective heat transfer coefficient calculated by correlation equations based on experimental results is used to evaluate the heat transfer between the fluid and the cooling pipe wall. The calculation time of the first method is about four times that of the second method. The simulation results of the two methods are consistent well at high flow rate, especially for turbulent flow. Therefore, the second method was used to perform thermal simulation under different cooling conditions and RF power levels. The influence of thermal radiation on the heat load to the cryogenic environment was also given in this paper. Simulation results show that thermal radiation has a slight impact on the heat load. When the copper emissivity equal to 0.02, the total static and dynamic heat load to 4.5 K are 0.833 W and 2.614 W at the power level of 200 kW, and the heat load to 4.5 K cryogenic environment caused by thermal radiation is 0.065 W.

Energy recovery operation for continuous-wave X-ray free-electron lasers

A superconducting linear accelerator operating in continuous-wave mode could produce X-ray free electron lasers (XFEL) at megahertz repetition rate, with the capability that delivering wide spectral range coherent radiation to multi end stations. In this paper, the energy recovery Linac (ERL) mode is proposed to flexibly control the electron beam energy for a continuous-wave superconducting Linac. Theoretical investigations and multi-dimensional numerical simulations are applied to the Linac case of Shanghai high-repetition-rate XFEL and extreme light facility. The results show that, with ERL operation in the last 25 cryo-modules, the strict requirements on RF power system could be significantly relaxed. And if one exhaust the RF power, the maximum electron beam energy can be enhanced from 8.74 GeV to 11.41 GeV in ERL mode. The optimization of the ERL operation, the multi-energy electron beam transport and the XFEL performance improvements are presented.

Alpha-buckets in High Energy Electron Storage Rings (Review of Existing Experiments and Feasibility Studies for Future Developments)

Electron storage rings operating at high energies have proven to be invaluable source of synchrotron radiation. Two and even three simultaneous beams of particles have been observed at different light source facilities worldwide. So called alpha-buckets were studied at Metrological Light Source (MLS) in Berlin (Germany), SOLEIL facility in France, DIAMOND light source in UK, NSLS ring in Brookhaven (USA). It is widely recognized that alpha buckets are general phenomena which is not restricted to a certain storage ring. However, earlier measurements showed essential limitations on parameters of alpha-buckets, strong dependence on high order (sextupole and octupoles) magnetic field imperfections and associated fast decay of electron current as well as reduced life time. Also a rising relevance of high order non-linear longitudinal beam dynamics is associated with new generation of diffraction limited light sources (DLSR) approaches, which all suffer nonlinear momentum compaction factor. A large variety of future generation electron synchrotrons require a comprehensive investigation of the physical processes involved into the operation of such rings. In this paper, we present review of high order non-linear longitudinal beam dynamics based on the longitudinal equations of motion and Hamiltonian expanded to a high order of the momentum compaction factor. Roots of the third order equation with a free term are derived in a form suitable for analytical estimations. The momentum independent term of orbit lengthening due to particle transverse excursions is estimated and taken into account. The results from simulations were benchmarked against existing experiments at the Karlsruhe Research Accelerator (KARA), SOLEIL and MLS rings. Parameters of three simultaneous beams and alpha buckets at MLS and SOLEIL have been reproduced with high accuracy. General conditions for stable operation of alpha buckets are presented. Based on analytical formulas and computer simulations, studies of longitudinal motion at KARA have been performed with an objective to estimate feasibility of filling and storing of beam in α-buckets. A Computer model was used to describe the behavior and dynamics of simultaneous beams in the KARA storage ring

Longitudinal equilibrium density distribution of arbitrary filled bunches in presence of a passive harmonic cavity and the short range wakefield

We propose a novel scheme for the calculation of bunch profiles and synchronous phase shifts for arbitrary fill patterns in electron storage rings considering both the effects of the passive harmonic cavity and the short range wakefield. This scheme treats the bunch as a charge distribution rather than a point charge with a bunch form factor, and divides the voltage induced in the cavity into two groups: that induced by the previous passages and that by the present passage, where the latter is integrated with the short range wakefield from all the other vacuum components. An iteration loop for computing the bunch profiles, including a subloop using Newton iteration for calculating the synchronous phase deviations, is built and implemented into a matlab-based code. Using this code, we study the bunch lengthening and centroid transient effects for several possible fill patterns in the Hefei Advanced Light Facility storage ring under design. We find the method is very efficient, and the CPU time for the whole calculation on a regular personal computer is less than 30 seconds for each case even with more than 700 bunches. Using the case of a long gap fill as a benchmark example, both the results given by our code and the multiparticle tracking simulation with elegant are in very good agreement.