We will report on partially coherent undulator radiation simulations performed for the Hard X-ray Nanoprobe (HXN) beamline of NSLS-II with electron beam and X-ray optics instabilities taken into consideration. RF BPM and XBPM data were used to estimate values of these positional and angular instabilities for the partially coherent X-ray emission and propagation calculations with SRW code. These calculations allowed us to determine time-varying (due to the instabilities) intensity distributions and other characteristics of the X-ray radiation at important beamline locations, and estimate impacts of the instabilities on experimental data from coherent diffraction imaging experiments at HXN.
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.
We compare the general Coherent Mode Decomposition (CMD) method implemented in SRW code and the method making use of Hermite-Gaussian functions implemented in SPECTRA code, both methods being applied to partially coherent Undulator Radiation (UR). The comparison is made in terms of modes required for the same accuracy of presentation of 4D cross spectral density and Wigner function of UR for the same electron beam and undulator systems (corresponding to modern high-brightness light sources – currently operating NSLS-II and the planned upgrade of SPring-8). We show that, even though the pre-defined orthogonal analytical functions are not the exact eigenmodes of the partially coherent UR, their use can be perfectly justified in many cases for the UR, especially when limited computational resources are available for performing the numerical decomposition. Before analyzing the CMD results, we also illustrate excellent agreement between UR characteristics computed with SPECTRA and with SRW. All the presented comparisons, and the agreements found, confirm the validity of methods used by the codes and accuracy of their results.
The method of the Coherent Mode Decomposition (CMD) is applied to numerical wave propagation calculations
for partially-coherent X-rays, using the Fourier optics and compatible methods. Its CPU and memory efficiency
is discussed in various cases of the wavefront at the source and the beam waist. With the absence of the quadratic
phase terms, the required sampling density of the electric fields is effectively reduced. The problem size is thus
moderate and the method is feasible to be implemented on a single-node CPU server. In other cases, the same
argument holds with proper treatments of the quadratic phase terms. Tests on CMD and the modes propagation
are done for the case of the Coherent Hard X-ray beamline of the National Synchrotron Light Source II, using
the Synchrotron Radiation Workshop software. We observe a few hundred or less dominant decomposed modes
that resemble the electric fields converge to the wavefront intensity at a high accuracy of over 99%.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.