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X-RAY RUNS: Apply for Beamtime

2017  March 15 - April 24

2017  May 17 - June 29
2017  BTR deadline: 04/17/17

2017  October 11 - December 21
2017  Proposal deadline: 08/01/17
2017  BTR deadline: 09/10/17

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Monday, December 21, 2015, 3:00 pm

Georg Hoffstaetter
Cornell University

"An ERL Loop at Cornell"

Abstract: Over the past year, accelerator physicists from Cornell and Brookhaven National Laboratory (BNL) have developed a conceptual design for an ERL loop at CLASSE. This loop will serve as a prototype for the electron source for an electron-ion collider, which BNL hopes to build in the future. The loop will also develop ERL technology needed for an ERL X-ray source, making it a natural next step for CLASSE. Engineering of the ERL loop is expected to begin in early 2016, with construction to start the following year.

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Tuesday, November 24, 2015, 1:00 pm

Christoph Montag
BNL

"The 2015 eRHIC Ring-Ring Design"

Abstract: To minimize the technical risk of the future electron-ion collider eRHIC currently under study at BNL, the ring-ring scheme has been revisited over the summer of 2015. The goal of this study was a design that covers the full center-of-mass energy range from 32 to 141 GeV with an initial luminosity around 1033 cm-2 sec-1, upgradeable to 1034 cm-2 sec-1 later on. In this presentation the baseline design will be presented, and future upgrades will be discussed.

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Tuesday, November 24, 2015, 11:00 am

Teng Tan
Temple University

"Enhancement of Vortex Penetration Field on Bulk Nb Coated with a Layer of MgB2 Thin Film"

Abstract: One of the main sources of power dissipation in bulk Nb Superconducting Radio Frequency (SRF) cavities has been identified to be vortex penetration. Vortex penetration takes place when the magnetic field at the inner surface of an SRF cavity exceeds a critical field (vortex penetration field Hvp). I will present my work on the successful coating of bulk Nb structures with high quality MgB2 thin films. The Hvp of MgB2 thin films alone and MgB2 covered bulk Nb were both measured and it was observed that a ~200 nm MgB2 thin film covered bulk Nb structure has a 25% higher Hvp compared with bare Nb at 2.8 K. The enhancement of Hvp depends on the thickness of the MgB2 thin film. Theoretical calculations showed that depositing a single layer of MgB2 with an optimized thickness on Nb can result in a 60% enhancement of Hvp. The results of coating MgB2 thin film on a 6-GHz elliptical cavity will also be presented.

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Friday, November 20, 2015, 1:00 pm

Kei Sawada
RIKEN SPring-8 Center

"Berry-phase theory of X-ray dynamical diffraction"

Abstract: X-ray diffraction is useful for analyzing material structures. X-rays are usually scattered only once by a material because of tiny interaction between them. In nearly perfect crystals, multiple scatterings of X-rays should be taken into account. This phenomenon is called dynamical diffraction that is analogous to other waves in periodic systems: electrons in condensed matter physics, coupled oscillators in classical mechanics, microwaves in electric circuits, and so on. These waves are described by the Bloch functions, and have interesting properties in terms of geometry. A typical example is the Berry-phase approach. This enables us to understand complicated phenomena simply as effects of virtual monopoles defined in parameter space. As for X-ray dynamical diffraction, X-rays propagating through a strained crystal are described by effective equation of motion with virtual magnetic monopole in phase space. In the talk, we will introduce basic ideas of the Berry-phase approach, and present its application to various systems as well as X-ray diffraction.

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Friday, October 23, 2015, 1:00 pm

Sarah L. Perry
Department of Chemical Engineering, University of Massachusetts Amherst

Hosted by: Richard Gillilan

"Microfluidic Platforms for Dynamic Protein Crystallography"

Abstract: Microfluidic chips for combinatorial analyses such as protein crystallization have advanced tremendously in recent years. These devices take advantage of miniscule sample volumes and parallel processing, while creating an environment free of inertial or convective effects and providing exquisite control over local conditions and gradients. The ability to create highly reproducible microenvironments has proven to be a tremendous asset for improving the consistency and quality of protein crystals grown on-chip. Coupling these benefits with advanced in situ protein crystallography techniques, microfluidics are poised to facilitate a wide range of structure-function studies than have previously been accessible.

The desire to observe protein structural dynamics in real time has generated renewed interest in room temperature diffraction studies. These efforts have been further supported by the use of serial crystallography, which aggregates small pieces of data from a large, uniform pool of crystals. We utilize a microfluidic crystallization platform for serial crystallography. This strategy takes advantage of integrated fluid handling and microfluidic geometries to enable the growth of a large number of high quality, isomorphous crystals, while eliminating the need for manual harvesting or manipulation of fragile crystals. We have demonstrated the efficacy of our approach for the de novo structure determination of a novel phosphonacetate hydrolase (PhnA) using single wavelength anomalous diffraction, and the time-resolved structural analysis of photoactive yellow protein (PYP) via Laue diffraction. We are currently working on using our methodologies to enable diffraction analysis of protein targets that are highly sensitive to radiation damage. In particular, we are looking to couple fast data collection with serial crystallography to minimize and/or “outrun” the effects radiation damage. These efforts also include adapting our microfluidic platforms to facilitate the analysis of microcrystals by decreasing the overall thickness of the device through the incorporation of novel materials such as graphene. Ultimately, our goal is to couple serial crystallography with the integrated fluid handling capabilities of combinatorial microfluidics to enable the use of chemical triggering (i.e., ligand addition) for time-resolved crystallography experiments.

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Monday, October 12, 2015, 1:00 pm

Laurent Deniau
CERN

"MAD: Methodical Accelerator Design"

Abstract: The MAD-X application and its predecessors are the workhorse for particles accelerator design at CERN for more than two decades, with active support to the community inside and outside the organisation. In this presentation, we will give an overview of the project over the past years and the future plans for the coming years. The MAD-X code is undergoing a complete redesign of its architecture and code quality, with a strong effort put on the understanding and improvement of the physics in order to prepare the next generation of MAD code. After exposing the particularities of MAD-X, we will discuss about important decision and development that had to be reviewed due to some recent event in the community of the selected technologies. Alternatives are under studies and progress will start again as soon as the evaluation is finalised.

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Friday, October 9, 2015, 1:00 pm

Justin Wozniak
Argonne National Lab

"Big Data Tools for Light Source Science"

Abstract: Synchrotron x-ray facilities, such as the Advanced Photon Source and Advanced Light Source, use a variety of scattering, imaging, and spectroscopic techniques to address a range of problems in materials science. The increasing brightness of such x-ray sources, coupled to recent developments in detector technologies, means that they must handle significantly greater data rates than in the past, both on individual beam lines and across facilities as a whole. Here we describe our approaches for for organizing both raw experimental data and subsequent derived data, managing and interacting with such large data over networks, and integrating large-scale high-performance computers. Our toolkit includes catalog, transfer, workflow, and GUI components. We will discuss the application of these techniques to accelerate real-time analysis of x-ray scattering data, thus improving the effectiveness of large-scale scientific investments.

Justin M. Wozniak is a Computer Scientist at Argonne National Laboratory (ANL). His research focuses on programming languages and storage systems for high-performance computers. He is closely connected with multiple scientific teams at the Advanced Photon Source at the ANL. He holds a Ph.D. from the University of Notre Dame, an MMath from the University of Waterloo, ON, and did undergraduate work at the University of Illinois at Urbana-Champaign in Computer Science, Mathematics, Chemistry, and Latin.

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Thursday, October 8, 2015, 1:00 pm

Jeffrey Eldred
Indiana University

"Slip-stacking at the Proton Intensity Frontier"

Abstract: I describe the state of research in slip-stacking and its future at Fermilab. Slip-stacking is an accumulation technique used to double the proton beam power for the NuMI neutrino research program. In slip-stacking, two particle beams of different momenta are stored in the same ring and are maintained by two RF cavities of different frequencies. Each beam is longitudinally focused by the one RF cavity and perturbed by the other. My work explores the dynamics of slip-stacking through theoretical, numerical, and experimental analysis. In addition, I’ve found a novel application of a harmonic cavity which greatly enhances the stability of slip-stacking. This discovery leads to the interesting possibility of continuing slip-stacking beyond the PIP-II era, delivering a multi-MW beam to a future LBNE/DUNE experiment.

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Monday, October 5, 2015, 1:00 pm

Jim Shanks
Cornell University

Hosted by: David Rubin

"CESR in the Age of Undulators: Operations and Lattice Design for CHESS"

Abstract: In 2014, two canted 104-pole undulators were installed in the Cornell Electron Storage Ring (CESR), bringing the Cornell High-Energy Synchrotron Source (CHESS) into the realm of third-generation x-ray light sources. These novel compact undulators have enabled a 250% increase in flux, while at the same time substantially decreasing the spot size compared to the original 49-pole wiggler.

This upgrade, however significant, is only the beginning. As DOE-funded light sources begin exploring upgrades to ultimate storage rings, CESR will require a reconfiguration in order to stay relevant in the field of x-ray science. In one scenario, the so-called South Arc upgrade, CHESS would move to single-beam operations, increase the beam energy from 5.3GeV to 6.0GeV, and build half a dozen new beam lines capable of accepting an undulator source. This upgrade could happen as soon as 2017, prior to the APS ring-wide upgrade.

In this talk I will cover a few operational aspects of present-day running with canted undulators in CESR. From there, I will discuss two options for the South Arc upgrade, either of which would increase the brilliance by nearly two orders of magnitude on beamlines already fed by undulators, and substantially more for bend-sourced beamlines.

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Monday, October 5, 2015, 10:00 pm

Jooseop Lee
Oakridge National Lab

Hosted by: Jacob Ruff

"Neutron Scattering Studies on Strongly Correlated Systems"

Abstract: Neutron scattering is an excellent tool to study strongly correlated systems as it directly interacts with magnetic and lattice degrees of freedom in a material. One can determine where the atoms are and how they move by elastic and inelastic scattering method under various sample environments. In this talk, I will present several systems exhibiting striking emergent phenomena including superconductivity and multiferroicity.

LaO1-xFxBiS2 is a newly discovered layered superconductor family. The crystal structure and lattice vibration modes have been examined to uncover the origin of superconductivity. It is found that the low energy modes remain almost unchanged between nonsuperconducting and superconducting states either by F doping or by cooling through the transition temperature, revealing unconventional nature of superconductivity in this system [1]. CeO0.5F0.5BiS2, another member of BiS2 superconductors, shows a rare and interesting case of coexistence of ferromagnetism and superconductivity. Our neutron scattering results suggest that spins are aligned ferromagnetically and their interaction can be described by Ising-like Hamiltonian [2].

Co3TeO6 is a new type-II multiferroic exhibiting rich magnetic properties. It shows temperature dependent multi-k structure as well as a complex magnetic H-T phase diagram with multistep spin-flop transitions [3]. From the analysis of diffuse scattering, we find the change of correlation length and interaction direction as a function of temperature.

Additionally, I will give a brief introduction on the mini coil pulsed magnet setup reaching 30T now available at SNS. The design, characteristics, and recent experiments of the pulsed magnet will be discussed. I will conclude with possible future experiments with pulsed fields demonstrating the utility of the pulsed magnet setup in neutron scattering experiments.

References:
[1] J. Lee et. al., Phys. Rev. B 87, 205134 (2013)
[2] J. Lee et. al., Phys. Rev. B 90, 224410 (2014)
[3] J. L. Her et. al., Phys. Rev. B 84, 235123 (2011)

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Friday, October 2, 2015, 2:00 pm

Maxim Perelstein, Dave Rubin, Peter Wittich, Jim Alexander
Cornell University

Hosted by: Jim Alexander

"Dark Photon Search in e+e- Annihilation using the Wilson Synchrotron"

Abstract: The existence of dark matter, which cannot be composed of any of the Standard Model (SM) particles, motivates considering the possibility of new types of elementary particles which interact only feebly with the SM matter. An interesting possibility is a “dark photon”; a dark photon in the 10-100 MeV/c2 mass range is especially well motivated theoretically. In this talk, we will describe a proposal for an experiment to search for the dark photon in this mass range using a 5 GeV positron beam produced by the synchrotron at Cornell’s Wilson Laboratory. The apparatus, designed to be built with components from the now-retired CLEO and Babar experiments, measures photons and allows one to compute the missing mass event by event. The signature for dark photon production is a bump in the missing mass distribution; no assumptions need be made about decay modes of the dark photon.

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Thursday, October 1, 2015, 1:00 pm

Harsha Panuganti
Northern Illinois University

Hosted by: David Rubin

"The Development of High Brightness Electron Source Laboratory (HBESL) at Fermilab: From Start to Finish"

Abstract: At the beginning of 2012, an electron source development laboratory started to take its shape to continue the legacy of the decommissioned A0 Photoinjector (A0PI) at Fermilab. The new lab, named the High Brightness Electron Source Laboratory (HBESL), had academic and research goals of supporting higher education involving multidisciplinary research in electron beam (generation, acceleration and manipulation) experiments through Fermilab, university and industry collaboration. In this seminar, I will first discuss the re-commissioning and upgrade of HBESL and then present the e-beam generation and application experiments conducted at the facility. The beam generation experiments include exploring nonlinear photoemission from cesium telluride (Cs2Te) semiconductor photocathode using infrared laser, and field emission from carbon-based cathodes (carbon nanotube and diamond array) inside RF environment. I will later discuss the application experiments conducted at the facility to produce soft x-rays via inverse Compton scattering (ICS) using low energy (4 MeV) e-beam, and to generate uniformly filled ellipsoidal bunches and temporally shaped electron beams from the Cs2Te photocathode. I will end the seminar with a note of future implications for HBESL.

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Special Student Seminar:

Monday, August 24, 2015, 10:00 am

Note alternate location: 178 Rhodes Hall

Darren Pagan
Cornell University

"High Energy X-ray Diffraction Studies of Heterogeneous Slip in Plastically Deforming Single Crystals"

Abstract: The ability to quantitatively measure crystallographic slip processes in-situ as a crystal plastically deforms is critical for the advancement of micromechanical models. In the work to be presented, new experimental high energy X-ray diffraction techniques and analysis methods are implemented to study heterogeneous slip in deforming single crystals. First, a method for quantifying the amounts of heterogeneous slip on multiple slip systems using single crystal orientation pole figures is described. The method is applied to the study of orientation pole figures measured in-situ from a plastically deforming silicon single crystal. Next, results from an experiment studying slip localization using a novel high resolution diffraction technique are reported. In the experiment, three dimensional distributions of diffracted intensity are measured from a copper single crystal as a region of high slip forms during compression. The combination of experimental X-ray diffraction and finite element crystal plasticity simulation results provide insight into how sharp gradients of slip influence the development of misorientation in a deforming crystal, providing a ‘signature’ of slip localization during plastic deformation.

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Thursday, August 6, 2015, 1:00 pm

Johan Bengtsson
Brookhaven National Lab

"Ring-Based Synchrotron Light Sources: A Deterministic Approach"

Abstract: The mathematical framework for Hamiltonian dynamics, perturbed by classical radiation and quantum fluctuations, and related numerical and analytical methods provide for realistic modeling of modern ring-based synchrotron light sources; i.e., predictable results. Applications include: conceptual design, simulation of the accelerator for e.g. testing and validation of controls algorithms (aka "Virtual Accelerator"), and on-line model for model based control of commissioning and operations. By using signal processing and turn-by-turn BPM data it is also possible to calibrate and validate the nonlinear model for such a system, hence, "closing-the-loop".

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Wednesday, July 22, 2015, 1:00 pm

Marie-Paule Pileni
Distinguished Professor UPMC and Senior Researcher CEA

"Nano and Supra Crystals: Specific Chemical and Physical Properties"

Abstract: The crystallinity of nanoparticles called nanocrystallinity plays a marked role in the chemical and physical properties of nanocrystals. The change in the absorption profile of the localized surface plasmon resonance spectrum observed with polycrystalline and single domain nanocrystals is attributed to internal structural defects like twins, whose effect on the optical properties is not accounted for using current models in the literature. The nanocrystallinity of Au nanocrystals induces a splitting of the quadrupolar vibrational modes (l=2) whereas it does not markedly perturb the vibrational breathing mode (l=0) of nanocrystals. The latter was also observed with Co nanocrystals.

When the Co nanocrystals are self-assembled in a 2D hexagonal compact network, the final structure of Co nanocrystals subjected to oxygen at 200°C, shows a marked change with their sizes and nanocrystallinities (fcc, tcp, ε phase, amorphous) with formation of either hollow CoO nanocrystals, core/shell (Co/CoO) or CoO nanocrystals.

During these last two decades it has been demonstrated that, by slow evaporation of a colloidal solution of nanoparticles characterized by a low size distribution, the nanocrystals self-assembled in 3D crystalline structure called supracrystals. These supracrystals form either films or shaped/faceted aggregates. When the nanocrystals dispersed in solution are composed by a mixture of single domain and polycrystalline nanoparticles, at the end of the evaporation process, segregation takes place: the single domain nanocrystals self assembled in fcc triangular supracrystals whereas the polycrystalline nanoparticles form fcc film supracrystals. Their elastic moduli differ with the supracrystal growth process, the nanocrystallinity of the nanoparticles used as the building blocks and the coating agents.

Binary supracrystals (Co/Ag, Ag/Ag and Co/Co) are produced. The small nanocrystals are placed in the interstices of the large ones. Various structures are detected and usually agree with the hard sphere model developed for atomic binary systems. However, with Co/Ag binary system, the Co-Co magnetic interactions induces a markedly change the structure with formation of “quasi”supracrystals.

Similarly by using a mixture of single domain Co and Au nanocrystals, vicinal facets (high index plane) of Au supracrystals are produced whereas with Au polycrystalline nanoparticles segregation takes place and fcc supracrystals is produced.

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Thursday, July 2, 2015, 1:00 pm

James Hunter
Los Alamos National Lab

"Introduction to Recon and an Example Study: Evaluation of Computed Tomography of Mock Uranium Fuel Rods at the Advanced Photon Source"

Abstract: This talk presents a short overview of LANL’s computed tomography reconstruction code, Recon, followed by an example use of the code at the Advanced Photon Source (APS). Recon is a large C/C++ code that was begun at LANL in 2001 and has evolved into a general purpose CT reconstruction code which supports a range of reconstruction algorithms and parallel processing modalities. This talk focuses on a high level overview of why Recon was written, what its capabilities are as well as the pros and cons of using Recon vs. existing commercial alternatives. Following this an example use of Recon on synchrotron data is presented. This example was a multi-year effort to evaluate the utility of computed tomography at a synchrotron (APS) as a tool for non-destructive evaluation of uranium fuel rods. The majority of the data presented is on mock material made with depleted uranium which mimics the x-ray attenuation characteristics of fuel rods while allowing for simpler handling. A range of data is presented including full thickness (5mm diameter) fuel rodlets, reduced thickness (1.8mm) sintering test samples, and pre/post irradiation samples (< 1mm thick). These data were taken on both a white beam (bending magnet) beamline and a high energy, monochromatic beamline. This data shows the utility of a synchrotron type source in the evealuation of manufacturing defects (pre-irradiation) and lays out the case for in situ CT of fuel pellet sintering. In addition data is shown from small post-irradiation samples and a case is made for post-irradiation CT of larger samples.

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Monday, June 29, 2015, 1:00 pm

Dr. Daniel Velazquez
Illinois Institute of Technology

"Synthesis of Ultra-Thin Single Crystal MgO/Ag/MgO Multilayer for Controlled Photocathode Emissive Properties"

Abstract: Photocathode emission properties are critical for electron beam applications such as photoinjectors for free electron lasers (FEL) and energy recovery Linacs (ERL). We investigate whether emission properties of photocathodes can be manipulated through the engineering of the surface electronic structure. The multilayers described here have been predicted to have emission properties in correlation with the film thickness [Phys. Rev. Lett. 104, 046801 (2010)]. In this talk, I will discuss the synthesis and characterization of multilayered MgO/Ag/MgO films in the (001) and (111) crystallographic orientations. For this purpose various techniques were used such as Reflection High-Energy Electron Diffraction (RHEED), Scanning Tunneling Microscopy (STM), Scanning Electron Microscopy/Energy Dispersive Spectroscopy (EDS) and Photoelectron Spectroscopy (PES) to show the formation of the crystalline and chemical structure of the multilayered films. The Kelvin Probe technique and Angle Resolved Photoelectron Spectroscopy were used to probe the correlation between the photoemissive properties of the multilayered surfaces with thickness.

Presentation: (PDF)

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Thursday, June 4, 2015, 2:00 pm

Jeremy Kowalczyk
University of Hawai`i at Manoa

I. "Radiated power and radiation reaction forces of coherently oscillating charged particles in classical electrodynamics"

Abstract: For the foreseeable future, the analysis and design of the complex systems needed to generate intense beams of radiation via the process of coherent emission into free-space will depend on the principles and methods of classical electrodynamics (CED). But the fields and forces predicted by the currently accepted CED theory are manifestly incompatible with Maxwell’s equations’ energy integral as applied to the process of coherent emission into free-space. It is the purpose of this presentation to review the evidence for these limitations of conventional CED, to identify an alternative formulation of CED that does not suffer from these defects, and to describe how the predictions of this more physically realistic formulation of electrodynamics, including the role of the advanced interactions allowed by Maxwell’s equations and thermodynamics, might be tested by experiment and applied to enhance the capabilities of devices and systems employing the mechanism of “radiation into free-space.”

Presentation I: (PowerPoint)

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II. "Optimized cavity-enhanced compact inverse-Compton X-ray source for semiconductor metrology"

Abstract: Electron-beam (ebeam) based light sources at major laboratories, spanning wavelengths from the terahertz to X-ray regions, have established their value in applications ranging from basic scientific research to homeland security. Development efforts are active for more compact, less expensive –but still capable and in ways superior– sources for installation and use on-site (at the location which they are critically needed) for such applications as semiconductor manufacturing, X-ray microscopy, and rock sample analysis to guide exploration by the mineral/energy industries. But further progress in the field requires standardization of the key transformative components of these sources, like the electron gun, to make these sources both capable and economical. We will discuss the development of a low-cost X-ray source at the University of Hawaii, the novel high-current thermionic electron gun employed in the source, and our efforts toward commercialization of the source for application to the manufacture of next-generation of semiconductor devices.

Presentation II: (PowerPoint)

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Friday, May 29, 2015, 1:00 pm

Giulia Papotti
CERN

"The LHC at higher energy: from the First Long Shutdown to Beam Commissioning for Run 2"

Abstract: The LHC has just come to the end of its first Long Shutdown and preparations are underway to prepare for Run 2 data taking at 13 TeV centre of mass energy. After briefly recalling the major work undertaken during the 2-year long LS1, details will be given of the cool-down and hardware commissioning phase where each individual superconducting circuit is individually qualified for operation at nominal current. For the main dipole circuits this phase was completed with a quench training campaign in order to operate reliably at the required field. In parallel to the training campaign a rigorous cold checkout has been used to qualify the machine as an ensemble and to establish the conditions necessary for beam operation. The details of this phase will be given together with associated dry runs and beam injection tests. Finally, the latest news will be presented concerning the beam commissioning of the machine in preparation for first physics operation, which will hopefully begin in June.

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Friday, May 22, 2015, 1:00 pm

Richard Stanek
Fermi National Laboratory

"LCLS-II Activities at Fermilab"

Abstract: Fermilab is one of the partner labs for the LCLS-II project, having responsibility for the 1.3 GHz and 3.9 GHz cryomodule design and the fabrication of one half of the cryomodules. The scope of work also includes design and fabrication of the Cryogenic Distribution System. Fermilab collaborates with Cornell and Jefferson Lab on R&D associated with High Q0 performance. A summary and status report on progress will be given emphasizing the design challenges associated with CW operation and the path forward.

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Monday, May 11, 2015, 1:30 pm

Jared Maxson
Cornell University, B Exam

"A Prescription for Optimal Beam Brightness from High Voltage DC Photoelectron Sources"

Abstract: High voltage DC photoelectron guns generating beams of 100s of kV are the sources of choice for a wide array of linear accelerators. For DC gun-driven, GeV-scale synchrotron light sources and meter-scale ultrafast electron diffraction beamlines alike, the beam's brightness is the principal figure of merit. Irrespective of the machine size, the beam brightness is limited by the parameters of the source: the extraction field and voltage, the drive laser 3D pulse shape, and the intrinsic momentum spread of the electrons leaving the photoemitting material. In this talk I'll describe a new experimental dc gun and beamline constructed at Cornell which has demonstrated the state of the art in each of these parameters, leading to a practical prescription for generating optimally bright beams.

Advisor: Ivan Bazarov

Presentation: (PowerPoint)

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Friday, April 10, 2015, 1:00 pm

Siddharth Karkare
Cornell University

"Ultra-low Emittance III-V Semiconductor Photocathodes"

Abstract: Performance of large (km scale) electron accelerators (used for high energy physics experiments and as x-ray sources) as well as smaller (m scale) ultra-fast electron diffraction setups is limited by the source of electrons. Low energy (< 1 eV) electrons obtained using visible light from III-V semiconductors activated to negative electron affinity (NEA) are ideal for these applications. Much of the physics behind the photoemission of electrons from such semiconductors is not well understood. A good understanding of this photoemission will enable design of novel materials that will have enhanced photoemission properties to improve the performance of the aforementioned applications. In this talk, I will present the theoretical, computational and experimental advances to achieve greater understanding of the photoemission process accomplished in the Cornell group over the last 2 years.

Presentation: (PowerPoint)

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Friday, March 20, 2015, 1:00 pm

Jesse Hopkins
Cornell University

"CryoSAXS: Progress and Prospects for the “coolest” new SAXS technique"

Abstract: What experiments would you run if you had 1000 times more sample, or 30 times better signal to noise? For biological small angle x-ray scattering (SAXS) experiments, these are not idle questions. Performing SAXS at cryogenic temperatures reduces sample radiation damage rates by orders of magnitude, allowing a commensurate reduction in sample volume or increase in exposure times. Work done at CHESS has demonstrated the feasibility of this technique, and is improving reliability and ease of use.

I will discuss the initial proof of concept, including identification of SAXS-friendly cryoprotectant conditions and early experiments in window-free variable-path-length cells. These have led to the development of low-volume fixed path-length sample holders for cryoSAXS, that eliminate many of the difficulties associated with the variable path-length sample holders. Scattering profiles collected at 100 K in either sample holder, from as little as 2.5 nL of illuminated volume, agree with room temperature measurements for standard molecules and yield envelope reconstructions that agree with measured atomic structures.

Substantial challenges must still be overcome to allow routine use of the technique by non-experts. Some of these are methods oriented, such as improvements in the sample holders and cooling techniques. Others are fundamental science questions, such as understanding the behavior of bulk solvent and macromolecule hydration layers at 100 K. I will briefly discuss the most pressing challenges and approaches to overcome them.

References:

A microfabricated fixed path length silicon sample holder improves background subtraction for cryoSAXS. J. B. Hopkins, A. M. Katz, S. P. Meisburger, M. A. Warkentin, R. E. Thorne, L. Pollack. Journal of Applied Crystallography, 48, 227-237 (2015).

Breaking the radiation damage limit with cryo-SAXS. S. P. Meisburger, M. Warkentin, H. Chen, J. B. Hopkins, R. E. Gillilan, L. Pollack and R. E. Thorne. Biophysical Journal 104, 227-236 (2013).

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Postponed until further notice

David Moncton
MIT

"TBA"

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Friday, February 20, 2015, 1:00 pm

George Srajer
Advanced Photon Source, Argonne National Laboratory
Argonne, IL

"Synchrotron Radiation Studies of Quantum Phase Transitions at the Advanced Photon Source*"

Abstract: Applied pressure has long been employed as an experimental tool for investigating the origins of magnetism in solid-state materials. More recently, such pressure studies have also become central to the study of quantum phase transitions (i.e., transitions that are driven by quantum rather than thermal fluctuations). We utilized the combination of a cryogenic diamond anvil cell and single-crystal synchrotron x-ray diffraction measurements to demonstrate the pressure-driven quantum critical regime in chromium, the elemental antiferromagnet.

In the second example, we studied the complex interplay of structural distortions and spin alignments. We show how a set of interacting quantum mechanical spins placed on the corners of square arrays in SrCu2(BO3)2, the model quantum magnet, evolves from a set of locally bonded entities to a globally ordered structure.

Finally, we describe the status of the dynamic compression beamline designed to study shock-wave induced phenomena utilizing imaging and diffraction techniques, and the intermediate energy x-ray beamline that has been optimized to study emergent phenomena via angle-resolved spectroscopy and resonant soft x-ray scattering.

*This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

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SPring-8-II

Monday, February 2, 2015, 1:00 pm

Dr. Ryota Kinjo
SPring-8-II
Riken, Japan

"The Structural Reform of Undulators at SPring-8-II"

Abstract: Dr. Kinjo will discuss his work on developing a lightweight, compact and cost-effective undulator having the magnetic force cancellation system.

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