RadiaSoft (United States)

We present an experimental and simulation-based investigation of the temporal evolution of light emission from a thin, laser-ionized helium plasma source. We demonstrate an analytic model to calculate the approximate scaling of the time-integrated, on-axis light emission with the initial plasma density and temperature, supported by the experiment, which enhances the understanding of plasma light measurement for plasma wakefield accelerator (PWFA) plasma sources. Our model simulates the plasma density and temperature using a split-step Fourier code and a particle-in-cell code. A fluid simulation is then used to model the plasma and neutral density, and the electron temperature as a function of time and position. We then show the numerical results of the space-and-time-resolved light emission and that collisional excitation is the dominant source of light emission. We validate our model by measuring the light emitted by a laser-ionized plasma using a novel statistical method capable of resolving the nanosecond-scale temporal dynamics of the plasma light using a cost-effective camera with microsecond-scale timing jitter. This method is ideal for deployment in the high radiation environment of a particle accelerator that precludes the use of expensive nanosecond-gated cameras. Our results show that our models can effectively simulate the dynamics of a thin, laser-ionized plasma source. In addition, this work provides a detailed understanding of the plasma light measurement, which is one of the few diagnostic signals available for the direct measurement of PWFA plasma sources.

We present a novel approach to the accurate and rapid propagation of general 2D wavefronts via linear canonical transforms. An operator splitting approach divides both the crystal and the amplified laser pulse into slices, so that the algorithms remain 2D for an intrinsically 3D problem. The Synchrotron Radiation Workshop (SRW) code uses these matrices to transform the wavefront with physical optics. We are also developing a Python library for linear canonical transforms, which will enable wavefront propagation via more general ABCD matrices. Comparisons with experimental data are presented.

Microphonics causes the cavity to detune. This study discusses the microphonics of sixteen 1.3 GHz cryomodules, 14 for LCLS-II and 2 for LCLS-II HE tested at CMTF. The peak detuning, as well as the RMS detuning for each cryomodule, will be discussed. For each cryomodule, the data was taken with enough soaking time to prevent any thermalization effects which can show up in the detuning. Each data capture taken was 30 minutes or longer and sampled at 1 kHz.

Machine protection at the Advanced Photon Source Upgrade (APS-U) storage ring (SR) will necessitate whole beam dumps capable of absorbing energy from 200 mA, 6 GeV, ultra-low emittance beams 1 . These beams will deliver acute doses of 30 MGy within 10-20 microseconds, and initial studies suggest that such rapid heating generates hydrodynamic expulsion of collimator material 2 . Subsequent emission patterns indicate the presence of plasma formation. For some bunch configurations, instantaneous magnetic fields can reach 1 T, which may constrain plasma motion within the strike region. We investigate the evolution of the irradiated material using FLASH, a publicly-available multi-physics code with robust magnetohydrodynamics solvers 3 . We first define transition conditions for vaporization and fluid release, and evaluate the resulting fluid flow for a range of beam parameters and release criteria. We then consider strategies for incorporating magnetic field source terms originating during bunch passage. Bunch patterns and strike frequency are also examined as input conditions for determining the strength of the plasma response.

Neutron scattering makes invaluable contributions to the physical, chemical, and nanostructured materials sciences. Single crystal diffraction experiments collect volumetric scattering data sets representing the internal structure relations by combining datasets of many individual settings at different orientations, times and sample environment conditions. In particular, we consider data from the single-crystal diffraction experiments at ORNL.* A new technical approach for rapid, interactive visualization of remote neutron data is being explored. The NVIDIA IndeX 3D volumetric visualization framework** is being used via the HTML5 client viewer from NVIDIA, the ParaView plugin***, and new Jupyter notebooks, which will be released to the community with an open source license.

Undulator radiation from synchrotron light sources must be transported down a beamline from the source to the sample. A partially coherent photon beam may be represented in phase space using a Wigner function, and its transport may use some similar techniques as is familiar in particle beam transport. We describe this process in the case that the beamline is composed of linear focusing and defocusing sections as well as apertures. We present a compact representation of the beamline map involving linear transformations and convolutions. We create a 1:1 imaging system (4f system) with a single slit on the image plane and observe the radiation downstream to it. We propagate a Gaussian beam and undulator radiation down this sample beamline, drawing parameters from current and future ultra low emittance light sources. We derive an analytic expression for the partially coherent Gaussian case including passage through a single slit aperture. We benchmark the Wigner function calculation against the analytical expression and a partially coherent calculation in the Synchrotron Radiation Workshop (SRW) code.

Detailed simulations of experiments carried out at modern light sources are directly related to the most efficient and productive use of these facilities for research in multiple branches of science and technology. The “Synchrotron Radiation Workshop” computer code with its Python interface, and Sirepo web-browser-based graphical user interface, currently supports physical optics simulations of coherent X-ray scattering and imaging experiments on user-defined virtual samples. We present examples of simulations of coherent scattering experiments that are typically performed at the Coherent Hard X-ray beamline at Brookhaven National Laboratory’s (BNL) National Synchrotron Light Source II. We also present several comparisons of the simulations with the results of actual coherent X-ray scattering experiments with nano-fabricated test samples produced at BNL’s Center for Functional Nanomaterials.

The generation of high-brightness beams with ultra-low emittance using the plasma photocathode technique has gained significant traction in recent years. The practical execution of a combined plasma wakefield acceleration section and a laser injected typically requires a dual gas medium for precision ionization of low and high ionization thresholds. The concept can be partially simplified in experiment by replacing the plasma wakefield acceleration component with a dielectric wakefield acceleration scheme, sacrificing field gradient but maintaining low emittance beam generation. In this paper, we describe the progress on the design of a hybrid scheme, using laser injection in a gas medium within a dielectric wakefield accelerator structure. The proof-of-concept experiment is planned to take place at the Argonne Wakefield Accelerator.