A wavefront split propagator dedicated to the simulation of wavefront propagation through high-resolution x-ray nano-focusing optics system has been implemented in Synchrotron Radiation Workshop (SRW). The new propagator integrated the Shifted Angular Spectrum (Shift-AS) method and the sub-wavefront approach with SRW's original transmission optics and standard drift-space propagators. This approach allowed for a significant reduction of memory required for the simulation of wavefront propagation through Fresnel zone plates with very large numbers of zones and other high-resolution focusing optics while preserving the accuracy of the numerical wave-optics calculation. We introduce the two approaches, i.e., the sub-wavefront approach and Shift-AS approach, and describe their implementation and program structure in the new SRW’s wavefront split propagator. Using the potential Fresnel zone plates of Soft X-ray Nanoprobe (SXN) beamline at NSLS-II as examples, we demonstrate this new propagator, and report on its high accuracy and memory-saving capabilities by comparing the calculation result with those by the original propagators, and also point to future applications of this approach.

The Soft X-ray Nanoprobe (SXN) beamline, in development at Synchrotron NSLS-II under NEXT-II U.S. Department of Energy MIE project, is dedicated to soft x-ray scanning microscopy. It will offer researchers state-of-the-art soft x-ray nano-imaging and spectroscopy tools with world-leading coherent high photon flux in the energy range from 250 eV to 2500 eV and full polarization control with an aim to reach spatial resolution below 10 nm. It will provide element access from carbon (C) to sulfur (S) through K-edges and many other important elements through L- and M-edges. The primary endstation, nanoISM, will offer both a conventional Scanning Transmission X-ray Microscopy (STXM) mode, for high throughput 2D/3D absorption imaging, and a coherent diffractive imaging (ptychography) mode, for extra high spatial resolution. This article presents the design and status of the SXN beamline. The result of wave-optics- simulation allowed us to verify the beam performance from “source to sample” and supports the design of the beamline.

Detailed physical optics simulations of beamlines and experiments offer great value towards efficiently utilizing light source facilities. They make it possible to study their predicted behaviors under configurations which can be controlled more precisely than in physical experiments. Synchrotron Radiation Workshop (SRW) is a state-of-the-art software package for such simulations. Through its Python-based interface and browser-based interface Sirepo, SRW supports the definition of detailed optical schemes with many types of optical elements, and the simulation of radiation propagation through them. SRW has been mainly focused on CPU-based calculations; however, due to many of the operations being embarrassingly parallel, there is significant potential for accelerating these calculations using general-purpose GPU computation. In this work, the application of GPU accelerated computing to SRW for accelerating time-dependent coherent x-ray scattering experiments is discussed. A detailed simulation of a typical X-ray Photon Correlation Spectroscopy experiment for characterizing the dynamics of a colloidal sample was performed. Large improvements in simulation speed were demonstrated by converting the radiation propagation operations for the associated optical elements to use GPU computation. Combined with coherent mode decomposition, this resulted in a qualitative leap forward in the calculation speed and level of detail at which similar partially coherent scattering experiments can be simulated. These improvements have wide-ranging applications, such as assisting in the development of improved data processing methods and allowing for more detailed analysis of proposed experiments before using beam time.

Click to increase image sizeClick to decrease image size AcknowledgmentsWe would like to thank P. Elleaume (ESRF) for his decision to initiate the SRW project, J. Sutter (Diamond LS) and R. Celestre (ESRF) for their contributions to SRW, M. S. del Rio, R. Barrett (ESRF), M.-E. Couprie, O. Marcouille (SOLEIL), B. Nash, R. Nagler, P. Moeller, D. Bruhwiler (RadiaSoft), A. Wojdyla, K. Goldberg (LBNL/ALS), X. Shi, L. Rebuffi (ANL/APS), Q. Shen, W.-K. Lee, P. Zschack and J. Hill (BNL/NSLS-II) for collaborations, support, and fruitful discussions. The work was supported by US DOE Contracts No. DE-SC0012704 (NSLS-II Operations) and DE-SC0011237 (SBIR), and Field Work Proposal PS-017. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at LBNL, operated under Contract No. DE-AC02-05CH11231 using NERSC award BES-ERCAP0024810.Disclosure statementNo potential conflict of interest was reported by the authors.

Physical optics simulations for beamlines and experiments are essential for the effective use of synchrotron light source facilities such as NSLS-II at BNL. The SRW software package supports such source-to-detector simulations for coherent X-ray scattering and imaging experiments through its Python interface and Sirepo browser-based graphical user interface. This allows one to define custom sample models, assess the feasibility of an experiment, and estimate most appropriate beamline settings before using valuable beamtime. We discuss the recent use of general-purpose GPU resources and coherent mode decomposition algorithms in SRW to accelerate physical optics simulations with partially coherent X-rays. To illustrate these new capabilities, we describe simulations of typical time series of partially coherent scattering images used in X-ray Photon Correlation Spectroscopy (XPCS) experiments; aiming to characterize the nanoscale dynamics of a disordered sample, representing a solution of nanoparticles undergoing Brownian diffusion.

X-ray wavefront measurement is an important beam diagnostic tool, especially for the diffraction-limited X-ray beam. These in situ diagnostics give a better understanding of beam imperfections, and they enable feedback for possible corrections and/or optical alignment improvements. Hartmann wavefront sensing is one of the promising techniques to perform in situ X-ray wavefront measurements. In this work, a simulation tool of the X-ray Hartmann Wavefront Sensor (HWS) is developed under the Synchrotron Radiation Workshop (SRW) framework. Using this new simulation capability, one can take advantage of the full SRW package to simulate Hartmann wavefront sensing with the beam traveling from the X-ray source to the sample through different X-ray optical components. This SRW HWS simulation tool can help to optimize the wavefront sensor parameters for a specific X-ray energy range. It can also simulate an in situ wavefront measurement experiment with a particular beamline optical layout and predict the expected results of the wavefront measurement under different beamline configurations.

A fast dynamic aperture (DA) optimization method for storage rings has been developed through the use of reversal integration. Even if dynamical systems have an exact reversal symmetry, a numerical forward integration differs from its reversal. For a chaotic trajectory, cumulative round-off errors are scaled, which results in an exponential growth on the difference. The exponential effect is a generic chaos indicator which represents the sensitivity of the chaotic motion to its initial condition. The chaos indicator of the charged particle motion can be obtained by comparing the forward integrations of particle trajectories with corresponding reversals, a.k.a. "backward integrations.'' The indicator is observable even through short-term particle tracking simulations. Therefore, adopting it as an objective function could speed up optimization. The DA of the National Synchrotron Light Source II storage ring, and another test diffraction-limited light source ring, were optimized using this method for the purpose of demonstration.

The “Synchrotron Radiation Workshop” (SRW) computer code is extensively used for the development of insertion devices (IDs) and X-ray beamlines at the National Synchrotron Light Source II and at other light source facilities. Among frequently used types of SRW calculations are the calculations of spontaneous emission from an ID in a storage ring, physical optics based simulations of propagation of this partially-coherent radiation through a beamline, and the simulations of propagation of 3D time-dependent radiation pulses through instruments of X-ray Free-Electron Lasers (XFELs). The two types of radiation propagation calculations are CPU-intensive, therefore for each of them parallel algorithms have been developed in SRW. For the storage ring related calculations, the parallel processing was implemented using the Message Passing Interface (MPI). For the XFEL calculations, a shared memory approach provided by the Open Multi-Processing (OpenMP) was adopted. The two parallelization methods, and their implementation in SRW, have different advantages and drawbacks: the MPI-parallelization of partially-coherent calculations for storage rings has a good scaling, but over-consumes memory, whereas the OpenMP-parallelization of time-dependent XFEL calculations is memory-efficient, but it can only scale within one multi-core server. We are reporting the results of the efficiency tests of these two types of parallel calculations, obtained for representative optical schemes. The tests were performed on an isolated server as well on a large computer cluster - the US DOE’s NERSC scientific computing facility.

We performed fully- and partially-coherent synchrotron emission and propagation simulations with the "Synchrotron Radiation Workshop" computer code to analyze the performance of two soft X-ray beamlines under development at the National Synchrotron Light Source II: Soft X-ray Nanoprobe (SXN), and Angle-Resolved Photoemission Spectroscopy (ARPES) and Resonant Inelastic X-ray Scattering (RIXS) Imaging (ARI). The SXN beamline intends to provide high flux and high spatial resolution coherent soft X-ray imaging capabilities using both zone plate and lensless coherent imaging techniques. The ARI beamline aims to perform high flux ARPES and RIXS experiments with a focal spot size at the sample approaching 100 nm using highly-demagnifying mirrors in Kirkpatrick-Baez geometry. To accurately calculate the resolution and the degree of X-ray coherence provided by the two state-of-the-art beamlines, partial coherence effects are required to be taken into account in wave optics simulations for these two beamlines. In this talk, beamline performance parameters such as spot size, degree of coherence, flux, and energy resolution at the sample are presented. The effects of mirror surface slope errors on beamline performance were studied and some suggestions for further optimization are discussed.

An interleaved sextupole scheme using a cross-cell betatron phase cancellation technique is adopted as a candidate for a future upgrade to the NSLS-II lattice. The upgraded lattice will use as many NSLS-II installed magnets as possible, including 30 dipoles, which will create a triple bend achromat configuration. A 300 pm-rad horizontal beam emittance has already been achieved with the current configuration. The emittance can be further reduced to around 200 pm-rad with damping wigglers. Some new design concepts used in modern 4th-generation light sources, such as adopting longitudinal gradient bends and reverse bends, are incorporated into the design as well. The betatron phase-advance between sextupoles is designed to have a cross-cell interleaved cancellation pattern in the transverse planes. The dynamic aperture is sufficient to allow the conventional off-axis top-off injection. At the same time, a large energy acceptance looks promising and would ensure a sufficiently long beam lifetime.

"Synchrotron Radiation Workshop" (SRW) is an open source physical optics computer code for calculation of detailed characteristics of Synchrotron Radiation (SR) generated by relativistic electrons in magnetic fields of arbitrary configuration. SRW also supports high-accuracy simulations of fully- and partially-coherent radiation propagation through X-ray optical beamlines, facilitated by so-called “Virtual Beamline” module. In this present tech note, we discuss the nonlinear optimization features of SRW with emphasis on the optimization library in SRW. This optimization library not only can be used to optimize the simulation beamline in SRW, it also can be integrated with real beamline operations and optimize the parameters based on real measurements. We also show some demos of the optimization library recently developed in SRW.

In this paper, we explore a method to manipulate low energy electron bunches in a space charge dominated regime, and we use this method to design low energy linac bunch compressors to compress electron bunches in a space charge dominated regime. In the method, we use the space charge effects instead of avoiding them; i.e., we use the space charge forces to generate the required energy chirp instead of the ordinary method which uses the rf accelerating system to generate the chirp. We redefine the concepts of the dispersion function and beta functions in a space charge dominated regime to guide the optimization. Using this method, we study the low energy (5-22 MeV) linac bunch compressor design to produce short (similar to 150 fs) and small size (similar to 30 mu m) bunches for the electron beam slicing project. The low energy linac bunch compressors work in a space charge dominated regime, and the bunches at the downstream of the gun have a negative energy chirp due to the space charge effects. To provide compression for the negative energy chirped bunch, we design a positive R-56 dispersive section using a four-dipole chicane with several quadrupole magnets. We have designed low energy linac bunch compressors with different photocathode rf guns. For example, one linac bunch compressor with the BNL photocathode electron rf gun has achieved a low energy bunch with the 166 fs rms bunch length, 28 and 31 mu m rms beam size in the vertical and horizontal directions, respectively, at 5 MeV with 50 pC charge. Another example with LBNL's very-high frequency gun has achieved a low energy bunch with the 128 fs rms bunch length, 42 and 25 mu m rms beam size in the vertical and horizontal directions, respectively, at 22 MeV with 200 pC charge.

In the electron beam slicing scheme 1, 2 considered for National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory, when a low energy electron bunch crosses from top of a high energy storage ring electron bunch, its coulomb force will kick a short slice (slicing bunch) from the core (core bunch) of the storage ring electron bunch. The short slice bunch and the long core bunch when passing through the 3 m long U20 in-vacuum undulator will radiate X-ray pulses with pulse length ~150 fs and 30 ps respectively. To separate the satellite radiation from the core radiation, we propose a conceptual optical scheme allowing for the separation. To get reliable estimates of the separation performances, we apply the Synchrotron Radiation Workshop (SRW) physical optics computer code 3, 4 to study the wavefront propagation. As calculations show, at 7.8 keV, the separation signal-to-noise ratio can reach 5~12 and the satellite photon flux per pulse at sample can be 5000~20000 photons/0.1%BW with x-ray pulse length 150 ~ 330 fs depending on the separation method and the crossing angle between the low energy electron bunch and the high energy storage ring bunch. Since the repetition rate of the electron beam slicing system can reach 100 kHz, the average flux per second can reach 5 x 108 ` 2 x 10 9 photons/sec/0.1%BW.

When a low energy electron bunch (similar to 20 MeV) crosses from top of a high energy bunch (e.g., 3 GeV) at an angle (e.g., 45 degrees), the Coulomb force exerted on the high energy bunch by the low energy bunch will kick a very short (similar to 150 fs) slice from the core of the high energy bunch. The slice of electron bunch can generate ultrashort x-ray pulse. In this paper, we will give analytical expressions about the angular kicks dependence on the crossing angle by assuming a Gaussian distribution for the low energy bunch. Applying the analytical results to the storage ring bunch in NSLS-II [1], we will discuss the optimized parameters of the electron beam slicing system in order to obtain a very short slice bunch and a sufficient separation between the slice and the core bunch.

In the electron beam slicing method [1], a low energy bunch with very short and focused beam size is required to interact with the storage ring bunch. We have designed a low energy bunch compressor with BNL photo-cathode electron RF-gun [2] by applying simulation code PARMELA [3]. In this paper, in order to confirm the simulation result, we benchmark the simulation result from PARMELA with that from IMPACT-T [4] for our compressor with BNL RFgun. In order to increase the repetition rate of the electron beam slicing system, and change the compressor’s RF gun from BNL RF-gun to LBNL’s VHF gun [5] to redesign the compressor by applying IMPACT-T with both space charge effects and CSR effects considered. The benchmark between PARMELA and IMPACT-T has produced excellent agreement. The comparison of the CSR effects also shows the bunch can be compressed and focused to our desired size after optimization using code IMPACT-T with CSR effects turned on. The new compressor with high repetition rate still works in space charge dominated domain and the bunch with a negative energy chirp at the entrance of the chicane is compressed by a chicane with positive R56. After the optimization, we have achieved a low energy bunch with the 128 fs RMS bunch length, 42 μm and 25 μm RMS beam size in the vertical and horizontal directions respectively, at 22 MeV with 200 pC charge.

We propose a new method to generate ultrashort x- ray pulses using focused short low energy (similar to 20 MeV) electron bunches to create short slices of electrons from the circulating electron bunches in a synchrotron radiation storage ring. When a low energy electron bunch crosses from the top of a high energy storage ring electron bunch, its Coulomb force will kick a short slice from the core of the storage ring electron bunch. The separated slices, when passing through an undulator, will radiate ultrashort x- ray pulses at about 160 fs. We discuss the advantages, challenges, and provide data which confirm the feasibility of this new method.

We study a low energy (5MeV) bunch compressor design to produce a short (<200 fs) and small size (~30 μm) bunch for the electron beam slicing project [1]. In order to lower the cost of our system, we have designed a bunch compressor using only a BNL photo-cathode electron RF-gun and a four-dipole chicane with several matching and focusing quadruples. Because there is no acceleration after the RF-gun exit, the compressor works in space charge dominated domain and the bunch has a negative energy chirp due to space charge effect at the gun exit. To provide compression for the negative energy chirped bunch, the chicane has positive 56 R . After the optimization, we have achieved a low energy bunch with the 166fs RMS bunch length, 28 μm and 31 μm RMS beam size in vertical and horizontal direction separately, at 5 MeV with 50 pC charge. This result meets the basic required beam parameters for the electron beam slicing scheme.